// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2009-2011 Red Hat, Inc.
 *
 * Author: Mikulas Patocka <mpatocka@redhat.com>
 *
 * This file is released under the GPL.
 */

#include <linux/dm-bufio.h>

#include <linux/device-mapper.h>
#include <linux/dm-io.h>
#include <linux/slab.h>
#include <linux/sched/mm.h>
#include <linux/jiffies.h>
#include <linux/vmalloc.h>
#include <linux/shrinker.h>
#include <linux/module.h>
#include <linux/rbtree.h>
#include <linux/stacktrace.h>
#include <linux/jump_label.h>

#include "dm.h"

#define DM_MSG_PREFIX "bufio"

/*
 * Memory management policy:
 *      Limit the number of buffers to DM_BUFIO_MEMORY_PERCENT of main memory
 *      or DM_BUFIO_VMALLOC_PERCENT of vmalloc memory (whichever is lower).
 *      Always allocate at least DM_BUFIO_MIN_BUFFERS buffers.
 *      Start background writeback when there are DM_BUFIO_WRITEBACK_PERCENT
 *      dirty buffers.
 */
#define DM_BUFIO_MIN_BUFFERS            8

#define DM_BUFIO_MEMORY_PERCENT         2
#define DM_BUFIO_VMALLOC_PERCENT        25
#define DM_BUFIO_WRITEBACK_RATIO        3
#define DM_BUFIO_LOW_WATERMARK_RATIO    16

/*
 * The nr of bytes of cached data to keep around.
 */
#define DM_BUFIO_DEFAULT_RETAIN_BYTES   (256 * 1024)

/*
 * Align buffer writes to this boundary.
 * Tests show that SSDs have the highest IOPS when using 4k writes.
 */
#define DM_BUFIO_WRITE_ALIGN            4096

/*
 * dm_buffer->list_mode
 */
#define LIST_CLEAN      0
#define LIST_DIRTY      1
#define LIST_SIZE       2

#define SCAN_RESCHED_CYCLE      16

/*--------------------------------------------------------------*/

/*
 * Rather than use an LRU list, we use a clock algorithm where entries
 * are held in a circular list.  When an entry is 'hit' a reference bit
 * is set.  The least recently used entry is approximated by running a
 * cursor around the list selecting unreferenced entries. Referenced
 * entries have their reference bit cleared as the cursor passes them.
 */
struct lru_entry {
        struct list_head list;
        atomic_t referenced;
};

struct lru_iter {
        struct lru *lru;
        struct list_head list;
        struct lru_entry *stop;
        struct lru_entry *e;
};

struct lru {
        struct list_head *cursor;
        unsigned long count;

        struct list_head iterators;
};

/*--------------*/

static void lru_init(struct lru *lru)
{
        lru->cursor = NULL;
        lru->count = 0;
        INIT_LIST_HEAD(&lru->iterators);
}

static void lru_destroy(struct lru *lru)
{
        WARN_ON_ONCE(lru->cursor);
        WARN_ON_ONCE(!list_empty(&lru->iterators));
}

/*
 * Insert a new entry into the lru.
 */
static void lru_insert(struct lru *lru, struct lru_entry *le)
{
        /*
         * Don't be tempted to set to 1, makes the lru aspect
         * perform poorly.
         */
        atomic_set(&le->referenced, 0);

        if (lru->cursor) {
                list_add_tail(&le->list, lru->cursor);
        } else {
                INIT_LIST_HEAD(&le->list);
                lru->cursor = &le->list;
        }
        lru->count++;
}

/*--------------*/

/*
 * Convert a list_head pointer to an lru_entry pointer.
 */
static inline struct lru_entry *to_le(struct list_head *l)
{
        return container_of(l, struct lru_entry, list);
}

/*
 * Initialize an lru_iter and add it to the list of cursors in the lru.
 */
static void lru_iter_begin(struct lru *lru, struct lru_iter *it)
{
        it->lru = lru;
        it->stop = lru->cursor ? to_le(lru->cursor->prev) : NULL;
        it->e = lru->cursor ? to_le(lru->cursor) : NULL;
        list_add(&it->list, &lru->iterators);
}

/*
 * Remove an lru_iter from the list of cursors in the lru.
 */
static inline void lru_iter_end(struct lru_iter *it)
{
        list_del(&it->list);
}

/* Predicate function type to be used with lru_iter_next */
typedef bool (*iter_predicate)(struct lru_entry *le, void *context);

/*
 * Advance the cursor to the next entry that passes the
 * predicate, and return that entry.  Returns NULL if the
 * iteration is complete.
 */
static struct lru_entry *lru_iter_next(struct lru_iter *it,
                                       iter_predicate pred, void *context)
{
        struct lru_entry *e;

        while (it->e) {
                e = it->e;

                /* advance the cursor */
                if (it->e == it->stop)
                        it->e = NULL;
                else
                        it->e = to_le(it->e->list.next);

                if (pred(e, context))
                        return e;
        }

        return NULL;
}

/*
 * Invalidate a specific lru_entry and update all cursors in
 * the lru accordingly.
 */
static void lru_iter_invalidate(struct lru *lru, struct lru_entry *e)
{
        struct lru_iter *it;

        list_for_each_entry(it, &lru->iterators, list) {
                /* Move c->e forwards if necc. */
                if (it->e == e) {
                        it->e = to_le(it->e->list.next);
                        if (it->e == e)
                                it->e = NULL;
                }

                /* Move it->stop backwards if necc. */
                if (it->stop == e) {
                        it->stop = to_le(it->stop->list.prev);
                        if (it->stop == e)
                                it->stop = NULL;
                }
        }
}

/*--------------*/

/*
 * Remove a specific entry from the lru.
 */
static void lru_remove(struct lru *lru, struct lru_entry *le)
{
        lru_iter_invalidate(lru, le);
        if (lru->count == 1) {
                lru->cursor = NULL;
        } else {
                if (lru->cursor == &le->list)
                        lru->cursor = lru->cursor->next;
                list_del(&le->list);
        }
        lru->count--;
}

/*
 * Mark as referenced.
 */
static inline void lru_reference(struct lru_entry *le)
{
        atomic_set(&le->referenced, 1);
}

/*--------------*/

/*
 * Remove the least recently used entry (approx), that passes the predicate.
 * Returns NULL on failure.
 */
enum evict_result {
        ER_EVICT,
        ER_DONT_EVICT,
        ER_STOP, /* stop looking for something to evict */
};

typedef enum evict_result (*le_predicate)(struct lru_entry *le, void *context);

static struct lru_entry *lru_evict(struct lru *lru, le_predicate pred, void *context, bool no_sleep)
{
        unsigned long tested = 0;
        struct list_head *h = lru->cursor;
        struct lru_entry *le;

        if (!h)
                return NULL;
        /*
         * In the worst case we have to loop around twice. Once to clear
         * the reference flags, and then again to discover the predicate
         * fails for all entries.
         */
        while (tested < lru->count) {
                le = container_of(h, struct lru_entry, list);

                if (atomic_read(&le->referenced)) {
                        atomic_set(&le->referenced, 0);
                } else {
                        tested++;
                        switch (pred(le, context)) {
                        case ER_EVICT:
                                /*
                                 * Adjust the cursor, so we start the next
                                 * search from here.
                                 */
                                lru->cursor = le->list.next;
                                lru_remove(lru, le);
                                return le;

                        case ER_DONT_EVICT:
                                break;

                        case ER_STOP:
                                lru->cursor = le->list.next;
                                return NULL;
                        }
                }

                h = h->next;

                if (!no_sleep)
                        cond_resched();
        }

        return NULL;
}

/*--------------------------------------------------------------*/

/*
 * Buffer state bits.
 */
#define B_READING       0
#define B_WRITING       1
#define B_DIRTY         2

/*
 * Describes how the block was allocated:
 * kmem_cache_alloc(), __get_free_pages() or vmalloc().
 * See the comment at alloc_buffer_data.
 */
enum data_mode {
        DATA_MODE_SLAB = 0,
        DATA_MODE_KMALLOC = 1,
        DATA_MODE_GET_FREE_PAGES = 2,
        DATA_MODE_VMALLOC = 3,
        DATA_MODE_LIMIT = 4
};

struct dm_buffer {
        /* protected by the locks in dm_buffer_cache */
        struct rb_node node;

        /* immutable, so don't need protecting */
        sector_t block;
        void *data;
        unsigned char data_mode;                /* DATA_MODE_* */

        /*
         * These two fields are used in isolation, so do not need
         * a surrounding lock.
         */
        atomic_t hold_count;
        unsigned long last_accessed;

        /*
         * Everything else is protected by the mutex in
         * dm_bufio_client
         */
        unsigned long state;
        struct lru_entry lru;
        unsigned char list_mode;                /* LIST_* */
        blk_status_t read_error;
        blk_status_t write_error;
        unsigned int dirty_start;
        unsigned int dirty_end;
        unsigned int write_start;
        unsigned int write_end;
        struct list_head write_list;
        struct dm_bufio_client *c;
        void (*end_io)(struct dm_buffer *b, blk_status_t bs);
#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
#define MAX_STACK 10
        unsigned int stack_len;
        unsigned long stack_entries[MAX_STACK];
#endif
};

/*--------------------------------------------------------------*/

/*
 * The buffer cache manages buffers, particularly:
 *  - inc/dec of holder count
 *  - setting the last_accessed field
 *  - maintains clean/dirty state along with lru
 *  - selecting buffers that match predicates
 *
 * It does *not* handle:
 *  - allocation/freeing of buffers.
 *  - IO
 *  - Eviction or cache sizing.
 *
 * cache_get() and cache_put_and_wake() are threadsafe, you do not need
 * to protect these calls with a surrounding mutex.  All the other
 * methods are not threadsafe; they do use locking primitives, but
 * only enough to ensure get/put are threadsafe.
 */

struct buffer_tree {
        union {
                struct rw_semaphore lock;
                rwlock_t spinlock;
        } u;
        struct rb_root root;
} ____cacheline_aligned_in_smp;

struct dm_buffer_cache {
        struct lru lru[LIST_SIZE];
        /*
         * We spread entries across multiple trees to reduce contention
         * on the locks.
         */
        unsigned int num_locks;
        bool no_sleep;
        struct buffer_tree trees[];
};

static DEFINE_STATIC_KEY_FALSE(no_sleep_enabled);

static inline unsigned int cache_index(sector_t block, unsigned int num_locks)
{
        return dm_hash_locks_index(block, num_locks);
}

/* Get the buffer tree in the cache for the given block.  Doesn't lock it. */
static inline struct buffer_tree *cache_get_tree(struct dm_buffer_cache *bc,
                                                 sector_t block)
{
        return &bc->trees[cache_index(block, bc->num_locks)];
}

/* Lock the given buffer tree in the cache for reading. */
static inline void cache_read_lock(struct dm_buffer_cache *bc,
                                   struct buffer_tree *tree)
{
        if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
                read_lock_bh(&tree->u.spinlock);
        else
                down_read(&tree->u.lock);
}

/* Unlock the given buffer tree in the cache for reading. */
static inline void cache_read_unlock(struct dm_buffer_cache *bc,
                                     struct buffer_tree *tree)
{
        if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
                read_unlock_bh(&tree->u.spinlock);
        else
                up_read(&tree->u.lock);
}

/* Lock the given buffer tree in the cache for writing. */
static inline void cache_write_lock(struct dm_buffer_cache *bc,
                                    struct buffer_tree *tree)
{
        if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
                write_lock_bh(&tree->u.spinlock);
        else
                down_write(&tree->u.lock);
}

/* Unlock the given buffer tree in the cache for writing. */
static inline void cache_write_unlock(struct dm_buffer_cache *bc,
                                      struct buffer_tree *tree)
{
        if (static_branch_unlikely(&no_sleep_enabled) && bc->no_sleep)
                write_unlock_bh(&tree->u.spinlock);
        else
                up_write(&tree->u.lock);
}

/*
 * Sometimes we want to repeatedly get and drop locks as part of an iteration.
 * This struct helps avoid redundant drop and gets of the same lock.
 */
struct lock_history {
        struct dm_buffer_cache *cache;
        bool write;
        unsigned int previous;
        unsigned int no_previous;
};

static void lh_init(struct lock_history *lh, struct dm_buffer_cache *cache, bool write)
{
        lh->cache = cache;
        lh->write = write;
        lh->no_previous = cache->num_locks;
        lh->previous = lh->no_previous;
}

static void __lh_lock(struct lock_history *lh, unsigned int index)
{
        if (lh->write) {
                if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
                        write_lock_bh(&lh->cache->trees[index].u.spinlock);
                else
                        down_write(&lh->cache->trees[index].u.lock);
        } else {
                if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
                        read_lock_bh(&lh->cache->trees[index].u.spinlock);
                else
                        down_read(&lh->cache->trees[index].u.lock);
        }
}

static void __lh_unlock(struct lock_history *lh, unsigned int index)
{
        if (lh->write) {
                if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
                        write_unlock_bh(&lh->cache->trees[index].u.spinlock);
                else
                        up_write(&lh->cache->trees[index].u.lock);
        } else {
                if (static_branch_unlikely(&no_sleep_enabled) && lh->cache->no_sleep)
                        read_unlock_bh(&lh->cache->trees[index].u.spinlock);
                else
                        up_read(&lh->cache->trees[index].u.lock);
        }
}

/*
 * Make sure you call this since it will unlock the final lock.
 */
static void lh_exit(struct lock_history *lh)
{
        if (lh->previous != lh->no_previous) {
                __lh_unlock(lh, lh->previous);
                lh->previous = lh->no_previous;
        }
}

/*
 * Named 'next' because there is no corresponding
 * 'up/unlock' call since it's done automatically.
 */
static void lh_next(struct lock_history *lh, sector_t b)
{
        unsigned int index = cache_index(b, lh->no_previous); /* no_previous is num_locks */

        if (lh->previous != lh->no_previous) {
                if (lh->previous != index) {
                        __lh_unlock(lh, lh->previous);
                        __lh_lock(lh, index);
                        lh->previous = index;
                }
        } else {
                __lh_lock(lh, index);
                lh->previous = index;
        }
}

static inline struct dm_buffer *le_to_buffer(struct lru_entry *le)
{
        return container_of(le, struct dm_buffer, lru);
}

static struct dm_buffer *list_to_buffer(struct list_head *l)
{
        struct lru_entry *le = list_entry(l, struct lru_entry, list);

        return le_to_buffer(le);
}

static void cache_init(struct dm_buffer_cache *bc, unsigned int num_locks, bool no_sleep)
{
        unsigned int i;

        bc->num_locks = num_locks;
        bc->no_sleep = no_sleep;

        for (i = 0; i < bc->num_locks; i++) {
                if (no_sleep)
                        rwlock_init(&bc->trees[i].u.spinlock);
                else
                        init_rwsem(&bc->trees[i].u.lock);
                bc->trees[i].root = RB_ROOT;
        }

        lru_init(&bc->lru[LIST_CLEAN]);
        lru_init(&bc->lru[LIST_DIRTY]);
}

static void cache_destroy(struct dm_buffer_cache *bc)
{
        unsigned int i;

        for (i = 0; i < bc->num_locks; i++)
                WARN_ON_ONCE(!RB_EMPTY_ROOT(&bc->trees[i].root));

        lru_destroy(&bc->lru[LIST_CLEAN]);
        lru_destroy(&bc->lru[LIST_DIRTY]);
}

/*--------------*/

/*
 * not threadsafe, or racey depending how you look at it
 */
static inline unsigned long cache_count(struct dm_buffer_cache *bc, int list_mode)
{
        return bc->lru[list_mode].count;
}

static inline unsigned long cache_total(struct dm_buffer_cache *bc)
{
        return cache_count(bc, LIST_CLEAN) + cache_count(bc, LIST_DIRTY);
}

/*--------------*/

/*
 * Gets a specific buffer, indexed by block.
 * If the buffer is found then its holder count will be incremented and
 * lru_reference will be called.
 *
 * threadsafe
 */
static struct dm_buffer *__cache_get(const struct rb_root *root, sector_t block)
{
        struct rb_node *n = root->rb_node;
        struct dm_buffer *b;

        while (n) {
                b = container_of(n, struct dm_buffer, node);

                if (b->block == block)
                        return b;

                n = block < b->block ? n->rb_left : n->rb_right;
        }

        return NULL;
}

static void __cache_inc_buffer(struct dm_buffer *b)
{
        atomic_inc(&b->hold_count);
        WRITE_ONCE(b->last_accessed, jiffies);
}

static struct dm_buffer *cache_get(struct dm_buffer_cache *bc,
                                   struct buffer_tree *tree, sector_t block)
{
        struct dm_buffer *b;

        /* Assuming tree == cache_get_tree(bc, block) */
        cache_read_lock(bc, tree);
        b = __cache_get(&tree->root, block);
        if (b) {
                lru_reference(&b->lru);
                __cache_inc_buffer(b);
        }
        cache_read_unlock(bc, tree);

        return b;
}

/*--------------*/

typedef enum evict_result (*b_predicate)(struct dm_buffer *, void *);

/*
 * Evicts a buffer based on a predicate.  The oldest buffer that
 * matches the predicate will be selected.  In addition to the
 * predicate the hold_count of the selected buffer will be zero.
 */
struct evict_wrapper {
        struct lock_history *lh;
        b_predicate pred;
        void *context;
};

/*
 * Wraps the buffer predicate turning it into an lru predicate.  Adds
 * extra test for hold_count.
 */
static enum evict_result __evict_pred(struct lru_entry *le, void *context)
{
        struct evict_wrapper *w = context;
        struct dm_buffer *b = le_to_buffer(le);

        lh_next(w->lh, b->block);

        if (atomic_read(&b->hold_count))
                return ER_DONT_EVICT;

        return w->pred(b, w->context);
}

static struct dm_buffer *__cache_evict(struct dm_buffer_cache *bc, int list_mode,
                                       b_predicate pred, void *context,
                                       struct lock_history *lh)
{
        struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context};
        struct lru_entry *le;
        struct dm_buffer *b;

        le = lru_evict(&bc->lru[list_mode], __evict_pred, &w, bc->no_sleep);
        if (!le)
                return NULL;

        b = le_to_buffer(le);
        /* __evict_pred will have locked the appropriate tree. */
        rb_erase(&b->node, &cache_get_tree(bc, b->block)->root);

        return b;
}

static struct dm_buffer *cache_evict(struct dm_buffer_cache *bc, int list_mode,
                                     b_predicate pred, void *context)
{
        struct dm_buffer *b;
        struct lock_history lh;

        lh_init(&lh, bc, true);
        b = __cache_evict(bc, list_mode, pred, context, &lh);
        lh_exit(&lh);

        return b;
}

/*--------------*/

/*
 * Mark a buffer as clean or dirty. Not threadsafe.
 */
static void cache_mark(struct dm_buffer_cache *bc, struct buffer_tree *tree,
                       struct dm_buffer *b, int list_mode)
{
        /* Assuming tree == cache_get_tree(bc, b->block) */
        cache_write_lock(bc, tree);
        if (list_mode != b->list_mode) {
                lru_remove(&bc->lru[b->list_mode], &b->lru);
                b->list_mode = list_mode;
                lru_insert(&bc->lru[b->list_mode], &b->lru);
        }
        cache_write_unlock(bc, tree);
}

/*--------------*/

/*
 * Runs through the lru associated with 'old_mode', if the predicate matches then
 * it moves them to 'new_mode'.  Not threadsafe.
 */
static void __cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode,
                              b_predicate pred, void *context, struct lock_history *lh)
{
        struct lru_entry *le;
        struct dm_buffer *b;
        struct evict_wrapper w = {.lh = lh, .pred = pred, .context = context};

        while (true) {
                le = lru_evict(&bc->lru[old_mode], __evict_pred, &w, bc->no_sleep);
                if (!le)
                        break;

                b = le_to_buffer(le);
                b->list_mode = new_mode;
                lru_insert(&bc->lru[b->list_mode], &b->lru);
        }
}

static void cache_mark_many(struct dm_buffer_cache *bc, int old_mode, int new_mode,
                            b_predicate pred, void *context)
{
        struct lock_history lh;

        lh_init(&lh, bc, true);
        __cache_mark_many(bc, old_mode, new_mode, pred, context, &lh);
        lh_exit(&lh);
}

/*--------------*/

/*
 * Iterates through all clean or dirty entries calling a function for each
 * entry.  The callback may terminate the iteration early.  Not threadsafe.
 */

/*
 * Iterator functions should return one of these actions to indicate
 * how the iteration should proceed.
 */
enum it_action {
        IT_NEXT,
        IT_COMPLETE,
};

typedef enum it_action (*iter_fn)(struct dm_buffer *b, void *context);

static void __cache_iterate(struct dm_buffer_cache *bc, int list_mode,
                            iter_fn fn, void *context, struct lock_history *lh)
{
        struct lru *lru = &bc->lru[list_mode];
        struct lru_entry *le, *first;

        if (!lru->cursor)
                return;

        first = le = to_le(lru->cursor);
        do {
                struct dm_buffer *b = le_to_buffer(le);

                lh_next(lh, b->block);

                switch (fn(b, context)) {
                case IT_NEXT:
                        break;

                case IT_COMPLETE:
                        return;
                }
                cond_resched();

                le = to_le(le->list.next);
        } while (le != first);
}

static void cache_iterate(struct dm_buffer_cache *bc, int list_mode,
                          iter_fn fn, void *context)
{
        struct lock_history lh;

        lh_init(&lh, bc, false);
        __cache_iterate(bc, list_mode, fn, context, &lh);
        lh_exit(&lh);
}

/*--------------*/

/*
 * Passes ownership of the buffer to the cache. Returns false if the
 * buffer was already present (in which case ownership does not pass).
 * eg, a race with another thread.
 *
 * Holder count should be 1 on insertion.
 *
 * Not threadsafe.
 */
static bool __cache_insert(struct rb_root *root, struct dm_buffer *b)
{
        struct rb_node **new = &root->rb_node, *parent = NULL;
        struct dm_buffer *found;

        while (*new) {
                found = container_of(*new, struct dm_buffer, node);

                if (found->block == b->block)
                        return false;

                parent = *new;
                new = b->block < found->block ?
                        &found->node.rb_left : &found->node.rb_right;
        }

        rb_link_node(&b->node, parent, new);
        rb_insert_color(&b->node, root);

        return true;
}

static bool cache_insert(struct dm_buffer_cache *bc, struct buffer_tree *tree,
                         struct dm_buffer *b)
{
        bool r;

        if (WARN_ON_ONCE(b->list_mode >= LIST_SIZE))
                return false;

        /* Assuming tree == cache_get_tree(bc, b->block) */
        cache_write_lock(bc, tree);
        BUG_ON(atomic_read(&b->hold_count) != 1);
        r = __cache_insert(&tree->root, b);
        if (r)
                lru_insert(&bc->lru[b->list_mode], &b->lru);
        cache_write_unlock(bc, tree);

        return r;
}

/*--------------*/

/*
 * Removes buffer from cache, ownership of the buffer passes back to the caller.
 * Fails if the hold_count is not one (ie. the caller holds the only reference).
 *
 * Not threadsafe.
 */
static bool cache_remove(struct dm_buffer_cache *bc, struct buffer_tree *tree,
                         struct dm_buffer *b)
{
        bool r;

        /* Assuming tree == cache_get_tree(bc, b->block) */
        cache_write_lock(bc, tree);

        if (atomic_read(&b->hold_count) != 1) {
                r = false;
        } else {
                r = true;
                rb_erase(&b->node, &tree->root);
                lru_remove(&bc->lru[b->list_mode], &b->lru);
        }

        cache_write_unlock(bc, tree);

        return r;
}

/*--------------*/

typedef void (*b_release)(struct dm_buffer *);

static struct dm_buffer *__find_next(struct rb_root *root, sector_t block)
{
        struct rb_node *n = root->rb_node;
        struct dm_buffer *b;
        struct dm_buffer *best = NULL;

        while (n) {
                b = container_of(n, struct dm_buffer, node);

                if (b->block == block)
                        return b;

                if (block <= b->block) {
                        n = n->rb_left;
                        best = b;
                } else {
                        n = n->rb_right;
                }
        }

        return best;
}

static void __remove_range(struct dm_buffer_cache *bc,
                           struct rb_root *root,
                           sector_t begin, sector_t end,
                           b_predicate pred, b_release release)
{
        struct dm_buffer *b;

        while (true) {
                cond_resched();

                b = __find_next(root, begin);
                if (!b || (b->block >= end))
                        break;

                begin = b->block + 1;

                if (atomic_read(&b->hold_count))
                        continue;

                if (pred(b, NULL) == ER_EVICT) {
                        rb_erase(&b->node, root);
                        lru_remove(&bc->lru[b->list_mode], &b->lru);
                        release(b);
                }
        }
}

static void cache_remove_range(struct dm_buffer_cache *bc,
                               sector_t begin, sector_t end,
                               b_predicate pred, b_release release)
{
        unsigned int i;

        BUG_ON(bc->no_sleep);
        for (i = 0; i < bc->num_locks; i++) {
                down_write(&bc->trees[i].u.lock);
                __remove_range(bc, &bc->trees[i].root, begin, end, pred, release);
                up_write(&bc->trees[i].u.lock);
        }
}

/*----------------------------------------------------------------*/

/*
 * Linking of buffers:
 *      All buffers are linked to buffer_cache with their node field.
 *
 *      Clean buffers that are not being written (B_WRITING not set)
 *      are linked to lru[LIST_CLEAN] with their lru_list field.
 *
 *      Dirty and clean buffers that are being written are linked to
 *      lru[LIST_DIRTY] with their lru_list field. When the write
 *      finishes, the buffer cannot be relinked immediately (because we
 *      are in an interrupt context and relinking requires process
 *      context), so some clean-not-writing buffers can be held on
 *      dirty_lru too.  They are later added to lru in the process
 *      context.
 */
struct dm_bufio_client {
        struct block_device *bdev;
        unsigned int block_size;
        s8 sectors_per_block_bits;

        bool no_sleep;
        struct mutex lock;
        spinlock_t spinlock;

        int async_write_error;

        void (*alloc_callback)(struct dm_buffer *buf);
        void (*write_callback)(struct dm_buffer *buf);
        struct kmem_cache *slab_buffer;
        struct kmem_cache *slab_cache;
        struct dm_io_client *dm_io;

        struct list_head reserved_buffers;
        unsigned int need_reserved_buffers;

        unsigned int minimum_buffers;

        sector_t start;

        struct shrinker *shrinker;
        struct work_struct shrink_work;
        atomic_long_t need_shrink;

        wait_queue_head_t free_buffer_wait;

        struct list_head client_list;

        /*
         * Used by global_cleanup to sort the clients list.
         */
        unsigned long oldest_buffer;

        struct dm_buffer_cache cache; /* must be last member */
};

/*----------------------------------------------------------------*/

#define dm_bufio_in_request()   (!!current->bio_list)

static void dm_bufio_lock(struct dm_bufio_client *c)
{
        if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
                spin_lock_bh(&c->spinlock);
        else
                mutex_lock_nested(&c->lock, dm_bufio_in_request());
}

static void dm_bufio_unlock(struct dm_bufio_client *c)
{
        if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
                spin_unlock_bh(&c->spinlock);
        else
                mutex_unlock(&c->lock);
}

/*----------------------------------------------------------------*/

/*
 * Default cache size: available memory divided by the ratio.
 */
static unsigned long dm_bufio_default_cache_size;

/*
 * Total cache size set by the user.
 */
static unsigned long dm_bufio_cache_size;

/*
 * A copy of dm_bufio_cache_size because dm_bufio_cache_size can change
 * at any time.  If it disagrees, the user has changed cache size.
 */
static unsigned long dm_bufio_cache_size_latch;

static DEFINE_SPINLOCK(global_spinlock);

static unsigned int dm_bufio_max_age; /* No longer does anything */

static unsigned long dm_bufio_retain_bytes = DM_BUFIO_DEFAULT_RETAIN_BYTES;

static unsigned long dm_bufio_peak_allocated;
static unsigned long dm_bufio_allocated_kmem_cache;
static unsigned long dm_bufio_allocated_kmalloc;
static unsigned long dm_bufio_allocated_get_free_pages;
static unsigned long dm_bufio_allocated_vmalloc;
static unsigned long dm_bufio_current_allocated;

/*----------------------------------------------------------------*/

/*
 * The current number of clients.
 */
static int dm_bufio_client_count;

/*
 * The list of all clients.
 */
static LIST_HEAD(dm_bufio_all_clients);

/*
 * This mutex protects dm_bufio_cache_size_latch and dm_bufio_client_count
 */
static DEFINE_MUTEX(dm_bufio_clients_lock);

static struct workqueue_struct *dm_bufio_wq;
static struct work_struct dm_bufio_replacement_work;


#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
static void buffer_record_stack(struct dm_buffer *b)
{
        b->stack_len = stack_trace_save(b->stack_entries, MAX_STACK, 2);
}
#endif

/*----------------------------------------------------------------*/

static void adjust_total_allocated(struct dm_buffer *b, bool unlink)
{
        unsigned char data_mode;
        long diff;

        static unsigned long * const class_ptr[DATA_MODE_LIMIT] = {
                &dm_bufio_allocated_kmem_cache,
                &dm_bufio_allocated_kmalloc,
                &dm_bufio_allocated_get_free_pages,
                &dm_bufio_allocated_vmalloc,
        };

        data_mode = b->data_mode;
        diff = (long)b->c->block_size;
        if (unlink)
                diff = -diff;

        spin_lock(&global_spinlock);

        *class_ptr[data_mode] += diff;

        dm_bufio_current_allocated += diff;

        if (dm_bufio_current_allocated > dm_bufio_peak_allocated)
                dm_bufio_peak_allocated = dm_bufio_current_allocated;

        if (!unlink) {
                if (dm_bufio_current_allocated > dm_bufio_cache_size)
                        queue_work(dm_bufio_wq, &dm_bufio_replacement_work);
        }

        spin_unlock(&global_spinlock);
}

/*
 * Change the number of clients and recalculate per-client limit.
 */
static void __cache_size_refresh(void)
{
        if (WARN_ON(!mutex_is_locked(&dm_bufio_clients_lock)))
                return;
        if (WARN_ON(dm_bufio_client_count < 0))
                return;

        dm_bufio_cache_size_latch = READ_ONCE(dm_bufio_cache_size);

        /*
         * Use default if set to 0 and report the actual cache size used.
         */
        if (!dm_bufio_cache_size_latch) {
                (void)cmpxchg(&dm_bufio_cache_size, 0,
                              dm_bufio_default_cache_size);
                dm_bufio_cache_size_latch = dm_bufio_default_cache_size;
        }
}

/*
 * Allocating buffer data.
 *
 * Small buffers are allocated with kmem_cache, to use space optimally.
 *
 * For large buffers, we choose between get_free_pages and vmalloc.
 * Each has advantages and disadvantages.
 *
 * __get_free_pages can randomly fail if the memory is fragmented.
 * __vmalloc won't randomly fail, but vmalloc space is limited (it may be
 * as low as 128M) so using it for caching is not appropriate.
 *
 * If the allocation may fail we use __get_free_pages. Memory fragmentation
 * won't have a fatal effect here, but it just causes flushes of some other
 * buffers and more I/O will be performed. Don't use __get_free_pages if it
 * always fails (i.e. order > MAX_PAGE_ORDER).
 *
 * If the allocation shouldn't fail we use __vmalloc. This is only for the
 * initial reserve allocation, so there's no risk of wasting all vmalloc
 * space.
 */
static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
                               unsigned char *data_mode)
{
        if (unlikely(c->slab_cache != NULL)) {
                *data_mode = DATA_MODE_SLAB;
                return kmem_cache_alloc(c->slab_cache, gfp_mask);
        }

        if (unlikely(c->block_size < PAGE_SIZE)) {
                *data_mode = DATA_MODE_KMALLOC;
                return kmalloc(c->block_size, gfp_mask | __GFP_RECLAIMABLE);
        }

        if (c->block_size <= KMALLOC_MAX_SIZE &&
            gfp_mask & __GFP_NORETRY) {
                *data_mode = DATA_MODE_GET_FREE_PAGES;
                return (void *)__get_free_pages(gfp_mask,
                                                c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
        }

        *data_mode = DATA_MODE_VMALLOC;

        return __vmalloc(c->block_size, gfp_mask);
}

/*
 * Free buffer's data.
 */
static void free_buffer_data(struct dm_bufio_client *c,
                             void *data, unsigned char data_mode)
{
        switch (data_mode) {
        case DATA_MODE_SLAB:
                kmem_cache_free(c->slab_cache, data);
                break;

        case DATA_MODE_KMALLOC:
                kfree(data);
                break;

        case DATA_MODE_GET_FREE_PAGES:
                free_pages((unsigned long)data,
                           c->sectors_per_block_bits - (PAGE_SHIFT - SECTOR_SHIFT));
                break;

        case DATA_MODE_VMALLOC:
                vfree(data);
                break;

        default:
                DMCRIT("dm_bufio_free_buffer_data: bad data mode: %d",
                       data_mode);
                BUG();
        }
}

/*
 * Allocate buffer and its data.
 */
static struct dm_buffer *alloc_buffer(struct dm_bufio_client *c, gfp_t gfp_mask)
{
        struct dm_buffer *b = kmem_cache_alloc(c->slab_buffer, gfp_mask);

        if (!b)
                return NULL;

        b->c = c;

        b->data = alloc_buffer_data(c, gfp_mask, &b->data_mode);
        if (!b->data) {
                kmem_cache_free(c->slab_buffer, b);
                return NULL;
        }
        adjust_total_allocated(b, false);

#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
        b->stack_len = 0;
#endif
        return b;
}

/*
 * Free buffer and its data.
 */
static void free_buffer(struct dm_buffer *b)
{
        struct dm_bufio_client *c = b->c;

        adjust_total_allocated(b, true);
        free_buffer_data(c, b->data, b->data_mode);
        kmem_cache_free(c->slab_buffer, b);
}

/*
 *--------------------------------------------------------------------------
 * Submit I/O on the buffer.
 *
 * Bio interface is faster but it has some problems:
 *      the vector list is limited (increasing this limit increases
 *      memory-consumption per buffer, so it is not viable);
 *
 *      the memory must be direct-mapped, not vmalloced;
 *
 * If the buffer is small enough (up to DM_BUFIO_INLINE_VECS pages) and
 * it is not vmalloced, try using the bio interface.
 *
 * If the buffer is big, if it is vmalloced or if the underlying device
 * rejects the bio because it is too large, use dm-io layer to do the I/O.
 * The dm-io layer splits the I/O into multiple requests, avoiding the above
 * shortcomings.
 *--------------------------------------------------------------------------
 */

/*
 * dm-io completion routine. It just calls b->bio.bi_end_io, pretending
 * that the request was handled directly with bio interface.
 */
static void dmio_complete(unsigned long error, void *context)
{
        struct dm_buffer *b = context;

        b->end_io(b, unlikely(error != 0) ? BLK_STS_IOERR : 0);
}

static void use_dmio(struct dm_buffer *b, enum req_op op, sector_t sector,
                     unsigned int n_sectors, unsigned int offset,
                     unsigned short ioprio)
{
        int r;
        struct dm_io_request io_req = {
                .bi_opf = op,
                .notify.fn = dmio_complete,
                .notify.context = b,
                .client = b->c->dm_io,
        };
        struct dm_io_region region = {
                .bdev = b->c->bdev,
                .sector = sector,
                .count = n_sectors,
        };

        if (b->data_mode != DATA_MODE_VMALLOC) {
                io_req.mem.type = DM_IO_KMEM;
                io_req.mem.ptr.addr = (char *)b->data + offset;
        } else {
                io_req.mem.type = DM_IO_VMA;
                io_req.mem.ptr.vma = (char *)b->data + offset;
        }

        r = dm_io(&io_req, 1, &region, NULL, ioprio);
        if (unlikely(r))
                b->end_io(b, errno_to_blk_status(r));
}

static void bio_complete(struct bio *bio)
{
        struct dm_buffer *b = bio->bi_private;
        blk_status_t status = bio->bi_status;

        bio_uninit(bio);
        kfree(bio);
        b->end_io(b, status);
}

static void use_bio(struct dm_buffer *b, enum req_op op, sector_t sector,
                    unsigned int n_sectors, unsigned int offset,
                    unsigned short ioprio)
{
        struct bio *bio;
        char *ptr;
        unsigned int len;

        bio = bio_kmalloc(1, GFP_NOWAIT);
        if (!bio) {
                use_dmio(b, op, sector, n_sectors, offset, ioprio);
                return;
        }
        bio_init_inline(bio, b->c->bdev, 1, op);
        bio->bi_iter.bi_sector = sector;
        bio->bi_end_io = bio_complete;
        bio->bi_private = b;
        bio->bi_ioprio = ioprio;

        ptr = (char *)b->data + offset;
        len = n_sectors << SECTOR_SHIFT;

        bio_add_virt_nofail(bio, ptr, len);

        submit_bio(bio);
}

static inline sector_t block_to_sector(struct dm_bufio_client *c, sector_t block)
{
        sector_t sector;

        if (likely(c->sectors_per_block_bits >= 0))
                sector = block << c->sectors_per_block_bits;
        else
                sector = block * (c->block_size >> SECTOR_SHIFT);
        sector += c->start;

        return sector;
}

static void submit_io(struct dm_buffer *b, enum req_op op, unsigned short ioprio,
                      void (*end_io)(struct dm_buffer *, blk_status_t))
{
        unsigned int n_sectors;
        sector_t sector;
        unsigned int offset, end, align;

        b->end_io = end_io;

        sector = block_to_sector(b->c, b->block);

        if (op != REQ_OP_WRITE) {
                n_sectors = b->c->block_size >> SECTOR_SHIFT;
                offset = 0;
        } else {
                if (b->c->write_callback)
                        b->c->write_callback(b);
                offset = b->write_start;
                end = b->write_end;
                align = max(DM_BUFIO_WRITE_ALIGN,
                        bdev_physical_block_size(b->c->bdev));
                offset &= -align;
                end += align - 1;
                end &= -align;
                if (unlikely(end > b->c->block_size))
                        end = b->c->block_size;

                sector += offset >> SECTOR_SHIFT;
                n_sectors = (end - offset) >> SECTOR_SHIFT;
        }

        if (b->data_mode != DATA_MODE_VMALLOC)
                use_bio(b, op, sector, n_sectors, offset, ioprio);
        else
                use_dmio(b, op, sector, n_sectors, offset, ioprio);
}

/*
 *--------------------------------------------------------------
 * Writing dirty buffers
 *--------------------------------------------------------------
 */

/*
 * The endio routine for write.
 *
 * Set the error, clear B_WRITING bit and wake anyone who was waiting on
 * it.
 */
static void write_endio(struct dm_buffer *b, blk_status_t status)
{
        b->write_error = status;
        if (unlikely(status)) {
                struct dm_bufio_client *c = b->c;

                (void)cmpxchg(&c->async_write_error, 0,
                                blk_status_to_errno(status));
        }

        BUG_ON(!test_bit(B_WRITING, &b->state));

        smp_mb__before_atomic();
        clear_bit(B_WRITING, &b->state);
        smp_mb__after_atomic();

        wake_up_bit(&b->state, B_WRITING);
}

/*
 * Initiate a write on a dirty buffer, but don't wait for it.
 *
 * - If the buffer is not dirty, exit.
 * - If there some previous write going on, wait for it to finish (we can't
 *   have two writes on the same buffer simultaneously).
 * - Submit our write and don't wait on it. We set B_WRITING indicating
 *   that there is a write in progress.
 */
static void __write_dirty_buffer(struct dm_buffer *b,
                                 struct list_head *write_list)
{
        if (!test_bit(B_DIRTY, &b->state))
                return;

        clear_bit(B_DIRTY, &b->state);
        wait_on_bit_lock_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);

        b->write_start = b->dirty_start;
        b->write_end = b->dirty_end;

        if (!write_list)
                submit_io(b, REQ_OP_WRITE, IOPRIO_DEFAULT, write_endio);
        else
                list_add_tail(&b->write_list, write_list);
}

static void __flush_write_list(struct list_head *write_list)
{
        struct blk_plug plug;

        blk_start_plug(&plug);
        while (!list_empty(write_list)) {
                struct dm_buffer *b =
                        list_entry(write_list->next, struct dm_buffer, write_list);
                list_del(&b->write_list);
                submit_io(b, REQ_OP_WRITE, IOPRIO_DEFAULT, write_endio);
                cond_resched();
        }
        blk_finish_plug(&plug);
}

/*
 * Wait until any activity on the buffer finishes.  Possibly write the
 * buffer if it is dirty.  When this function finishes, there is no I/O
 * running on the buffer and the buffer is not dirty.
 */
static void __make_buffer_clean(struct dm_buffer *b)
{
        BUG_ON(atomic_read(&b->hold_count));

        /* smp_load_acquire() pairs with read_endio()'s smp_mb__before_atomic() */
        if (!smp_load_acquire(&b->state))       /* fast case */
                return;

        wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);
        __write_dirty_buffer(b, NULL);
        wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
}

static enum evict_result is_clean(struct dm_buffer *b, void *context)
{
        struct dm_bufio_client *c = context;

        /* These should never happen */
        if (WARN_ON_ONCE(test_bit(B_WRITING, &b->state)))
                return ER_DONT_EVICT;
        if (WARN_ON_ONCE(test_bit(B_DIRTY, &b->state)))
                return ER_DONT_EVICT;
        if (WARN_ON_ONCE(b->list_mode != LIST_CLEAN))
                return ER_DONT_EVICT;

        if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep &&
            unlikely(test_bit(B_READING, &b->state)))
                return ER_DONT_EVICT;

        return ER_EVICT;
}

static enum evict_result is_dirty(struct dm_buffer *b, void *context)
{
        /* These should never happen */
        if (WARN_ON_ONCE(test_bit(B_READING, &b->state)))
                return ER_DONT_EVICT;
        if (WARN_ON_ONCE(b->list_mode != LIST_DIRTY))
                return ER_DONT_EVICT;

        return ER_EVICT;
}

/*
 * Find some buffer that is not held by anybody, clean it, unlink it and
 * return it.
 */
static struct dm_buffer *__get_unclaimed_buffer(struct dm_bufio_client *c)
{
        struct dm_buffer *b;

        b = cache_evict(&c->cache, LIST_CLEAN, is_clean, c);
        if (b) {
                /* this also waits for pending reads */
                __make_buffer_clean(b);
                return b;
        }

        if (static_branch_unlikely(&no_sleep_enabled) && c->no_sleep)
                return NULL;

        b = cache_evict(&c->cache, LIST_DIRTY, is_dirty, NULL);
        if (b) {
                __make_buffer_clean(b);
                return b;
        }

        return NULL;
}

/*
 * Wait until some other threads free some buffer or release hold count on
 * some buffer.
 *
 * This function is entered with c->lock held, drops it and regains it
 * before exiting.
 */
static void __wait_for_free_buffer(struct dm_bufio_client *c)
{
        DECLARE_WAITQUEUE(wait, current);

        add_wait_queue(&c->free_buffer_wait, &wait);
        set_current_state(TASK_UNINTERRUPTIBLE);
        dm_bufio_unlock(c);

        /*
         * It's possible to miss a wake up event since we don't always
         * hold c->lock when wake_up is called.  So we have a timeout here,
         * just in case.
         */
        io_schedule_timeout(5 * HZ);

        remove_wait_queue(&c->free_buffer_wait, &wait);

        dm_bufio_lock(c);
}

enum new_flag {
        NF_FRESH = 0,
        NF_READ = 1,
        NF_GET = 2,
        NF_PREFETCH = 3
};

/*
 * Allocate a new buffer. If the allocation is not possible, wait until
 * some other thread frees a buffer.
 *
 * May drop the lock and regain it.
 */
static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client *c, enum new_flag nf)
{
        struct dm_buffer *b;
        bool tried_noio_alloc = false;

        /*
         * dm-bufio is resistant to allocation failures (it just keeps
         * one buffer reserved in cases all the allocations fail).
         * So set flags to not try too hard:
         *      GFP_NOWAIT: don't wait and don't print a warning in case of
         *                  failure; if we need to sleep we'll release our mutex
         *                  and wait ourselves.
         *      __GFP_NORETRY: don't retry and rather return failure
         *      __GFP_NOMEMALLOC: don't use emergency reserves
         *
         * For debugging, if we set the cache size to 1, no new buffers will
         * be allocated.
         */
        while (1) {
                if (dm_bufio_cache_size_latch != 1) {
                        b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC);
                        if (b)
                                return b;
                }

                if (nf == NF_PREFETCH)
                        return NULL;

                if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
                        dm_bufio_unlock(c);
                        b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
                        dm_bufio_lock(c);
                        if (b)
                                return b;
                        tried_noio_alloc = true;
                }

                if (!list_empty(&c->reserved_buffers)) {
                        b = list_to_buffer(c->reserved_buffers.next);
                        list_del(&b->lru.list);
                        c->need_reserved_buffers++;

                        return b;
                }

                b = __get_unclaimed_buffer(c);
                if (b)
                        return b;

                __wait_for_free_buffer(c);
        }
}

static struct dm_buffer *__alloc_buffer_wait(struct dm_bufio_client *c, enum new_flag nf)
{
        struct dm_buffer *b = __alloc_buffer_wait_no_callback(c, nf);

        if (!b)
                return NULL;

        if (c->alloc_callback)
                c->alloc_callback(b);

        return b;
}

/*
 * Free a buffer and wake other threads waiting for free buffers.
 */
static void __free_buffer_wake(struct dm_buffer *b)
{
        struct dm_bufio_client *c = b->c;

        b->block = -1;
        if (!c->need_reserved_buffers)
                free_buffer(b);
        else {
                list_add(&b->lru.list, &c->reserved_buffers);
                c->need_reserved_buffers--;
        }

        /*
         * We hold the bufio lock here, so no one can add entries to the
         * wait queue anyway.
         */
        if (unlikely(waitqueue_active(&c->free_buffer_wait)))
                wake_up(&c->free_buffer_wait);
}

static enum evict_result cleaned(struct dm_buffer *b, void *context)
{
        if (WARN_ON_ONCE(test_bit(B_READING, &b->state)))
                return ER_DONT_EVICT; /* should never happen */

        if (test_bit(B_DIRTY, &b->state) || test_bit(B_WRITING, &b->state))
                return ER_DONT_EVICT;
        else
                return ER_EVICT;
}

static void __move_clean_buffers(struct dm_bufio_client *c)
{
        cache_mark_many(&c->cache, LIST_DIRTY, LIST_CLEAN, cleaned, NULL);
}

struct write_context {
        int no_wait;
        struct list_head *write_list;
};

static enum it_action write_one(struct dm_buffer *b, void *context)
{
        struct write_context *wc = context;

        if (wc->no_wait && test_bit(B_WRITING, &b->state))
                return IT_COMPLETE;

        __write_dirty_buffer(b, wc->write_list);
        return IT_NEXT;
}

static void __write_dirty_buffers_async(struct dm_bufio_client *c, int no_wait,
                                        struct list_head *write_list)
{
        struct write_context wc = {.no_wait = no_wait, .write_list = write_list};

        __move_clean_buffers(c);
        cache_iterate(&c->cache, LIST_DIRTY, write_one, &wc);
}

/*
 * Check if we're over watermark.
 * If we are over threshold_buffers, start freeing buffers.
 * If we're over "limit_buffers", block until we get under the limit.
 */
static void __check_watermark(struct dm_bufio_client *c,
                              struct list_head *write_list)
{
        if (cache_count(&c->cache, LIST_DIRTY) >
            cache_count(&c->cache, LIST_CLEAN) * DM_BUFIO_WRITEBACK_RATIO)
                __write_dirty_buffers_async(c, 1, write_list);
}

/*
 *--------------------------------------------------------------
 * Getting a buffer
 *--------------------------------------------------------------
 */

static void cache_put_and_wake(struct dm_bufio_client *c,
                               struct buffer_tree *tree, struct dm_buffer *b)
{
        bool wake;

        /* Assuming tree == cache_get_tree(&c->cache, b->block) */
        cache_read_lock(&c->cache, tree);
        BUG_ON(!atomic_read(&b->hold_count));
        wake = atomic_dec_and_test(&b->hold_count);
        cache_read_unlock(&c->cache, tree);

        /*
         * Relying on waitqueue_active() is racey, but we sleep
         * with schedule_timeout anyway.
         */
        if (wake && unlikely(waitqueue_active(&c->free_buffer_wait)))
                wake_up(&c->free_buffer_wait);
}

/*
 * This assumes you have already checked the cache to see if the buffer
 * is already present (it will recheck after dropping the lock for allocation).
 */
static struct dm_buffer *__bufio_new(struct dm_bufio_client *c,
                                     struct buffer_tree *tree, sector_t block,
                                     enum new_flag nf, int *need_submit,
                                     struct list_head *write_list)
{
        struct dm_buffer *b, *new_b = NULL;

        *need_submit = 0;

        /* This can't be called with NF_GET */
        if (WARN_ON_ONCE(nf == NF_GET))
                return NULL;

        new_b = __alloc_buffer_wait(c, nf);
        if (!new_b)
                return NULL;

        /*
         * We've had a period where the mutex was unlocked, so need to
         * recheck the buffer tree.
         */
        b = cache_get(&c->cache, tree, block);
        if (b) {
                __free_buffer_wake(new_b);
                goto found_buffer;
        }

        __check_watermark(c, write_list);

        b = new_b;
        atomic_set(&b->hold_count, 1);
        WRITE_ONCE(b->last_accessed, jiffies);
        b->block = block;
        b->read_error = 0;
        b->write_error = 0;
        b->list_mode = LIST_CLEAN;

        if (nf == NF_FRESH)
                b->state = 0;
        else {
                b->state = 1 << B_READING;
                *need_submit = 1;
        }

        /*
         * We mustn't insert into the cache until the B_READING state
         * is set.  Otherwise another thread could get it and use
         * it before it had been read.
         */
        cache_insert(&c->cache, tree, b);

        return b;

found_buffer:
        if (nf == NF_PREFETCH) {
                cache_put_and_wake(c, tree, b);
                return NULL;
        }

        /*
         * Note: it is essential that we don't wait for the buffer to be
         * read if dm_bufio_get function is used. Both dm_bufio_get and
         * dm_bufio_prefetch can be used in the driver request routine.
         * If the user called both dm_bufio_prefetch and dm_bufio_get on
         * the same buffer, it would deadlock if we waited.
         */
        if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state))) {
                cache_put_and_wake(c, tree, b);
                return NULL;
        }

        return b;
}

/*
 * The endio routine for reading: set the error, clear the bit and wake up
 * anyone waiting on the buffer.
 */
static void read_endio(struct dm_buffer *b, blk_status_t status)
{
        b->read_error = status;

        BUG_ON(!test_bit(B_READING, &b->state));

        smp_mb__before_atomic();
        clear_bit(B_READING, &b->state);
        smp_mb__after_atomic();

        wake_up_bit(&b->state, B_READING);
}

/*
 * A common routine for dm_bufio_new and dm_bufio_read.  Operation of these
 * functions is similar except that dm_bufio_new doesn't read the
 * buffer from the disk (assuming that the caller overwrites all the data
 * and uses dm_bufio_mark_buffer_dirty to write new data back).
 */
static void *new_read(struct dm_bufio_client *c, sector_t block,
                      enum new_flag nf, struct dm_buffer **bp,
                      unsigned short ioprio)
{
        struct buffer_tree *tree;
        int need_submit = 0;
        struct dm_buffer *b;

        LIST_HEAD(write_list);

        *bp = NULL;

        /*
         * Fast path, hopefully the block is already in the cache.  No need
         * to get the client lock for this.
         */
        tree = cache_get_tree(&c->cache, block);
        b = cache_get(&c->cache, tree, block);
        if (b) {
                if (nf == NF_PREFETCH) {
                        cache_put_and_wake(c, tree, b);
                        return NULL;
                }

                /*
                 * Note: it is essential that we don't wait for the buffer to be
                 * read if dm_bufio_get function is used. Both dm_bufio_get and
                 * dm_bufio_prefetch can be used in the driver request routine.
                 * If the user called both dm_bufio_prefetch and dm_bufio_get on
                 * the same buffer, it would deadlock if we waited.
                 */
                if (nf == NF_GET && unlikely(test_bit_acquire(B_READING, &b->state))) {
                        cache_put_and_wake(c, tree, b);
                        return NULL;
                }
        }

        if (!b) {
                if (nf == NF_GET)
                        return NULL;

                dm_bufio_lock(c);
                b = __bufio_new(c, tree, block, nf, &need_submit, &write_list);
                dm_bufio_unlock(c);
        }

#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
        if (b && (atomic_read(&b->hold_count) == 1))
                buffer_record_stack(b);
#endif

        __flush_write_list(&write_list);

        if (!b)
                return NULL;

        if (need_submit)
                submit_io(b, REQ_OP_READ, ioprio, read_endio);

        if (nf != NF_GET)       /* we already tested this condition above */
                wait_on_bit_io(&b->state, B_READING, TASK_UNINTERRUPTIBLE);

        if (b->read_error) {
                int error = blk_status_to_errno(b->read_error);

                dm_bufio_release(b);

                return ERR_PTR(error);
        }

        *bp = b;

        return b->data;
}

void *dm_bufio_get(struct dm_bufio_client *c, sector_t block,
                   struct dm_buffer **bp)
{
        return new_read(c, block, NF_GET, bp, IOPRIO_DEFAULT);
}
EXPORT_SYMBOL_GPL(dm_bufio_get);

static void *__dm_bufio_read(struct dm_bufio_client *c, sector_t block,
                        struct dm_buffer **bp, unsigned short ioprio)
{
        if (WARN_ON_ONCE(dm_bufio_in_request()))
                return ERR_PTR(-EINVAL);

        return new_read(c, block, NF_READ, bp, ioprio);
}

void *dm_bufio_read(struct dm_bufio_client *c, sector_t block,
                    struct dm_buffer **bp)
{
        return __dm_bufio_read(c, block, bp, IOPRIO_DEFAULT);
}
EXPORT_SYMBOL_GPL(dm_bufio_read);

void *dm_bufio_read_with_ioprio(struct dm_bufio_client *c, sector_t block,
                                struct dm_buffer **bp, unsigned short ioprio)
{
        return __dm_bufio_read(c, block, bp, ioprio);
}
EXPORT_SYMBOL_GPL(dm_bufio_read_with_ioprio);

void *dm_bufio_new(struct dm_bufio_client *c, sector_t block,
                   struct dm_buffer **bp)
{
        if (WARN_ON_ONCE(dm_bufio_in_request()))
                return ERR_PTR(-EINVAL);

        return new_read(c, block, NF_FRESH, bp, IOPRIO_DEFAULT);
}
EXPORT_SYMBOL_GPL(dm_bufio_new);

static void __dm_bufio_prefetch(struct dm_bufio_client *c,
                        sector_t block, unsigned int n_blocks,
                        unsigned short ioprio)
{
        struct blk_plug plug;

        LIST_HEAD(write_list);

        if (WARN_ON_ONCE(dm_bufio_in_request()))
                return; /* should never happen */

        blk_start_plug(&plug);

        for (; n_blocks--; block++) {
                struct buffer_tree *tree;
                struct dm_buffer *b;
                int need_submit;

                tree = cache_get_tree(&c->cache, block);
                b = cache_get(&c->cache, tree, block);
                if (b) {
                        /* already in cache */
                        cache_put_and_wake(c, tree, b);
                        continue;
                }

                dm_bufio_lock(c);
                b = __bufio_new(c, tree, block, NF_PREFETCH, &need_submit,
                                &write_list);
                if (unlikely(!list_empty(&write_list))) {
                        dm_bufio_unlock(c);
                        blk_finish_plug(&plug);
                        __flush_write_list(&write_list);
                        blk_start_plug(&plug);
                        dm_bufio_lock(c);
                }
                if (unlikely(b != NULL)) {
                        dm_bufio_unlock(c);

                        if (need_submit)
                                submit_io(b, REQ_OP_READ, ioprio, read_endio);
                        dm_bufio_release(b);

                        cond_resched();

                        if (!n_blocks)
                                goto flush_plug;
                        dm_bufio_lock(c);
                }
                dm_bufio_unlock(c);
        }

flush_plug:
        blk_finish_plug(&plug);
}

void dm_bufio_prefetch(struct dm_bufio_client *c, sector_t block, unsigned int n_blocks)
{
        return __dm_bufio_prefetch(c, block, n_blocks, IOPRIO_DEFAULT);
}
EXPORT_SYMBOL_GPL(dm_bufio_prefetch);

void dm_bufio_prefetch_with_ioprio(struct dm_bufio_client *c, sector_t block,
                                unsigned int n_blocks, unsigned short ioprio)
{
        return __dm_bufio_prefetch(c, block, n_blocks, ioprio);
}
EXPORT_SYMBOL_GPL(dm_bufio_prefetch_with_ioprio);

void dm_bufio_release(struct dm_buffer *b)
{
        struct dm_bufio_client *c = b->c;
        struct buffer_tree *tree = cache_get_tree(&c->cache, b->block);

        /*
         * If there were errors on the buffer, and the buffer is not
         * to be written, free the buffer. There is no point in caching
         * invalid buffer.
         */
        if ((b->read_error || b->write_error) &&
            !test_bit_acquire(B_READING, &b->state) &&
            !test_bit(B_WRITING, &b->state) &&
            !test_bit(B_DIRTY, &b->state)) {
                dm_bufio_lock(c);

                /* cache remove can fail if there are other holders */
                if (cache_remove(&c->cache, tree, b)) {
                        __free_buffer_wake(b);
                        dm_bufio_unlock(c);
                        return;
                }

                dm_bufio_unlock(c);
        }

        cache_put_and_wake(c, tree, b);
}
EXPORT_SYMBOL_GPL(dm_bufio_release);

void dm_bufio_mark_partial_buffer_dirty(struct dm_buffer *b,
                                        unsigned int start, unsigned int end)
{
        struct dm_bufio_client *c = b->c;

        BUG_ON(start >= end);
        BUG_ON(end > b->c->block_size);

        dm_bufio_lock(c);

        BUG_ON(test_bit(B_READING, &b->state));

        if (!test_and_set_bit(B_DIRTY, &b->state)) {
                b->dirty_start = start;
                b->dirty_end = end;
                cache_mark(&c->cache, cache_get_tree(&c->cache, b->block), b,
                           LIST_DIRTY);
        } else {
                if (start < b->dirty_start)
                        b->dirty_start = start;
                if (end > b->dirty_end)
                        b->dirty_end = end;
        }

        dm_bufio_unlock(c);
}
EXPORT_SYMBOL_GPL(dm_bufio_mark_partial_buffer_dirty);

void dm_bufio_mark_buffer_dirty(struct dm_buffer *b)
{
        dm_bufio_mark_partial_buffer_dirty(b, 0, b->c->block_size);
}
EXPORT_SYMBOL_GPL(dm_bufio_mark_buffer_dirty);

void dm_bufio_write_dirty_buffers_async(struct dm_bufio_client *c)
{
        LIST_HEAD(write_list);

        if (WARN_ON_ONCE(dm_bufio_in_request()))
                return; /* should never happen */

        dm_bufio_lock(c);
        __write_dirty_buffers_async(c, 0, &write_list);
        dm_bufio_unlock(c);
        __flush_write_list(&write_list);
}
EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers_async);

/*
 * For performance, it is essential that the buffers are written asynchronously
 * and simultaneously (so that the block layer can merge the writes) and then
 * waited upon.
 *
 * Finally, we flush hardware disk cache.
 */
static bool is_writing(struct lru_entry *e, void *context)
{
        struct dm_buffer *b = le_to_buffer(e);

        return test_bit(B_WRITING, &b->state);
}

int dm_bufio_write_dirty_buffers(struct dm_bufio_client *c)
{
        int a, f;
        unsigned long nr_buffers;
        struct lru_entry *e;
        struct lru_iter it;

        LIST_HEAD(write_list);

        dm_bufio_lock(c);
        __write_dirty_buffers_async(c, 0, &write_list);
        dm_bufio_unlock(c);
        __flush_write_list(&write_list);
        dm_bufio_lock(c);

        nr_buffers = cache_count(&c->cache, LIST_DIRTY);
        lru_iter_begin(&c->cache.lru[LIST_DIRTY], &it);
        while ((e = lru_iter_next(&it, is_writing, c))) {
                struct dm_buffer *b = le_to_buffer(e);
                struct buffer_tree *tree;
                __cache_inc_buffer(b);

                BUG_ON(test_bit(B_READING, &b->state));

                if (nr_buffers) {
                        nr_buffers--;
                        dm_bufio_unlock(c);
                        wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
                        dm_bufio_lock(c);
                } else {
                        wait_on_bit_io(&b->state, B_WRITING, TASK_UNINTERRUPTIBLE);
                }

                tree = cache_get_tree(&c->cache, b->block);

                if (!test_bit(B_DIRTY, &b->state) && !test_bit(B_WRITING, &b->state))
                        cache_mark(&c->cache, tree, b, LIST_CLEAN);

                cache_put_and_wake(c, tree, b);

                cond_resched();
        }
        lru_iter_end(&it);

        wake_up(&c->free_buffer_wait);
        dm_bufio_unlock(c);

        a = xchg(&c->async_write_error, 0);
        f = dm_bufio_issue_flush(c);
        if (a)
                return a;

        return f;
}
EXPORT_SYMBOL_GPL(dm_bufio_write_dirty_buffers);

/*
 * Use dm-io to send an empty barrier to flush the device.
 */
int dm_bufio_issue_flush(struct dm_bufio_client *c)
{
        struct dm_io_request io_req = {
                .bi_opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC,
                .mem.type = DM_IO_KMEM,
                .mem.ptr.addr = NULL,
                .client = c->dm_io,
        };
        struct dm_io_region io_reg = {
                .bdev = c->bdev,
                .sector = 0,
                .count = 0,
        };

        if (WARN_ON_ONCE(dm_bufio_in_request()))
                return -EINVAL;

        return dm_io(&io_req, 1, &io_reg, NULL, IOPRIO_DEFAULT);
}
EXPORT_SYMBOL_GPL(dm_bufio_issue_flush);

/*
 * Use dm-io to send a discard request to flush the device.
 */
int dm_bufio_issue_discard(struct dm_bufio_client *c, sector_t block, sector_t count)
{
        struct dm_io_request io_req = {
                .bi_opf = REQ_OP_DISCARD | REQ_SYNC,
                .mem.type = DM_IO_KMEM,
                .mem.ptr.addr = NULL,
                .client = c->dm_io,
        };
        struct dm_io_region io_reg = {
                .bdev = c->bdev,
                .sector = block_to_sector(c, block),
                .count = block_to_sector(c, count),
        };

        if (WARN_ON_ONCE(dm_bufio_in_request()))
                return -EINVAL; /* discards are optional */

        return dm_io(&io_req, 1, &io_reg, NULL, IOPRIO_DEFAULT);
}
EXPORT_SYMBOL_GPL(dm_bufio_issue_discard);

static void forget_buffer(struct dm_bufio_client *c, sector_t block)
{
        struct buffer_tree *tree = cache_get_tree(&c->cache, block);
        struct dm_buffer *b;

        b = cache_get(&c->cache, tree, block);
        if (b) {
                if (likely(!smp_load_acquire(&b->state))) {
                        if (cache_remove(&c->cache, tree, b))
                                __free_buffer_wake(b);
                        else
                                cache_put_and_wake(c, tree, b);
                } else {
                        cache_put_and_wake(c, tree, b);
                }
        }
}

/*
 * Free the given buffer.
 *
 * This is just a hint, if the buffer is in use or dirty, this function
 * does nothing.
 */
void dm_bufio_forget(struct dm_bufio_client *c, sector_t block)
{
        dm_bufio_lock(c);
        forget_buffer(c, block);
        dm_bufio_unlock(c);
}
EXPORT_SYMBOL_GPL(dm_bufio_forget);

static enum evict_result idle(struct dm_buffer *b, void *context)
{
        return b->state ? ER_DONT_EVICT : ER_EVICT;
}

void dm_bufio_forget_buffers(struct dm_bufio_client *c, sector_t block, sector_t n_blocks)
{
        dm_bufio_lock(c);
        cache_remove_range(&c->cache, block, block + n_blocks, idle, __free_buffer_wake);
        dm_bufio_unlock(c);
}
EXPORT_SYMBOL_GPL(dm_bufio_forget_buffers);

void dm_bufio_set_minimum_buffers(struct dm_bufio_client *c, unsigned int n)
{
        c->minimum_buffers = n;
}
EXPORT_SYMBOL_GPL(dm_bufio_set_minimum_buffers);

unsigned int dm_bufio_get_block_size(struct dm_bufio_client *c)
{
        return c->block_size;
}
EXPORT_SYMBOL_GPL(dm_bufio_get_block_size);

sector_t dm_bufio_get_device_size(struct dm_bufio_client *c)
{
        sector_t s = bdev_nr_sectors(c->bdev);

        if (s >= c->start)
                s -= c->start;
        else
                s = 0;
        if (likely(c->sectors_per_block_bits >= 0))
                s >>= c->sectors_per_block_bits;
        else
                sector_div(s, c->block_size >> SECTOR_SHIFT);
        return s;
}
EXPORT_SYMBOL_GPL(dm_bufio_get_device_size);

struct dm_io_client *dm_bufio_get_dm_io_client(struct dm_bufio_client *c)
{
        return c->dm_io;
}
EXPORT_SYMBOL_GPL(dm_bufio_get_dm_io_client);

sector_t dm_bufio_get_block_number(struct dm_buffer *b)
{
        return b->block;
}
EXPORT_SYMBOL_GPL(dm_bufio_get_block_number);

void *dm_bufio_get_block_data(struct dm_buffer *b)
{
        return b->data;
}
EXPORT_SYMBOL_GPL(dm_bufio_get_block_data);

void *dm_bufio_get_aux_data(struct dm_buffer *b)
{
        return b + 1;
}
EXPORT_SYMBOL_GPL(dm_bufio_get_aux_data);

struct dm_bufio_client *dm_bufio_get_client(struct dm_buffer *b)
{
        return b->c;
}
EXPORT_SYMBOL_GPL(dm_bufio_get_client);

static enum it_action warn_leak(struct dm_buffer *b, void *context)
{
        bool *warned = context;

        WARN_ON(!(*warned));
        *warned = true;
        DMERR("leaked buffer %llx, hold count %u, list %d",
              (unsigned long long)b->block, atomic_read(&b->hold_count), b->list_mode);
#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
        stack_trace_print(b->stack_entries, b->stack_len, 1);
        /* mark unclaimed to avoid WARN_ON at end of drop_buffers() */
        atomic_set(&b->hold_count, 0);
#endif
        return IT_NEXT;
}

static void drop_buffers(struct dm_bufio_client *c)
{
        int i;
        struct dm_buffer *b;

        if (WARN_ON(dm_bufio_in_request()))
                return; /* should never happen */

        /*
         * An optimization so that the buffers are not written one-by-one.
         */
        dm_bufio_write_dirty_buffers_async(c);

        dm_bufio_lock(c);

        while ((b = __get_unclaimed_buffer(c)))
                __free_buffer_wake(b);

        for (i = 0; i < LIST_SIZE; i++) {
                bool warned = false;

                cache_iterate(&c->cache, i, warn_leak, &warned);
        }

#ifdef CONFIG_DM_DEBUG_BLOCK_STACK_TRACING
        while ((b = __get_unclaimed_buffer(c)))
                __free_buffer_wake(b);
#endif

        for (i = 0; i < LIST_SIZE; i++)
                WARN_ON(cache_count(&c->cache, i));

        dm_bufio_unlock(c);
}

static unsigned long get_retain_buffers(struct dm_bufio_client *c)
{
        unsigned long retain_bytes = READ_ONCE(dm_bufio_retain_bytes);

        if (likely(c->sectors_per_block_bits >= 0))
                retain_bytes >>= c->sectors_per_block_bits + SECTOR_SHIFT;
        else
                retain_bytes /= c->block_size;

        return retain_bytes;
}

static void __scan(struct dm_bufio_client *c)
{
        int l;
        struct dm_buffer *b;
        unsigned long freed = 0;
        unsigned long retain_target = get_retain_buffers(c);
        unsigned long count = cache_total(&c->cache);

        for (l = 0; l < LIST_SIZE; l++) {
                while (true) {
                        if (count - freed <= retain_target)
                                atomic_long_set(&c->need_shrink, 0);
                        if (!atomic_long_read(&c->need_shrink))
                                break;

                        b = cache_evict(&c->cache, l,
                                        l == LIST_CLEAN ? is_clean : is_dirty, c);
                        if (!b)
                                break;

                        __make_buffer_clean(b);
                        __free_buffer_wake(b);

                        atomic_long_dec(&c->need_shrink);
                        freed++;

                        if (unlikely(freed % SCAN_RESCHED_CYCLE == 0)) {
                                dm_bufio_unlock(c);
                                cond_resched();
                                dm_bufio_lock(c);
                        }
                }
        }
}

static void shrink_work(struct work_struct *w)
{
        struct dm_bufio_client *c = container_of(w, struct dm_bufio_client, shrink_work);

        dm_bufio_lock(c);
        __scan(c);
        dm_bufio_unlock(c);
}

static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
{
        struct dm_bufio_client *c;

        c = shrink->private_data;
        atomic_long_add(sc->nr_to_scan, &c->need_shrink);
        queue_work(dm_bufio_wq, &c->shrink_work);

        return sc->nr_to_scan;
}

static unsigned long dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
{
        struct dm_bufio_client *c = shrink->private_data;
        unsigned long count = cache_total(&c->cache);
        unsigned long retain_target = get_retain_buffers(c);
        unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);

        if (unlikely(count < retain_target))
                count = 0;
        else
                count -= retain_target;

        if (unlikely(count < queued_for_cleanup))
                count = 0;
        else
                count -= queued_for_cleanup;

        return count;
}

/*
 * Create the buffering interface
 */
struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsigned int block_size,
                                               unsigned int reserved_buffers, unsigned int aux_size,
                                               void (*alloc_callback)(struct dm_buffer *),
                                               void (*write_callback)(struct dm_buffer *),
                                               unsigned int flags)
{
        int r;
        unsigned int num_locks;
        struct dm_bufio_client *c;
        char slab_name[64];
        static atomic_t seqno = ATOMIC_INIT(0);

        if (!block_size || block_size & ((1 << SECTOR_SHIFT) - 1)) {
                DMERR("%s: block size not specified or is not multiple of 512b", __func__);
                r = -EINVAL;
                goto bad_client;
        }

        num_locks = dm_num_hash_locks();
        c = kzalloc(sizeof(*c) + (num_locks * sizeof(struct buffer_tree)), GFP_KERNEL);
        if (!c) {
                r = -ENOMEM;
                goto bad_client;
        }
        cache_init(&c->cache, num_locks, (flags & DM_BUFIO_CLIENT_NO_SLEEP) != 0);

        c->bdev = bdev;
        c->block_size = block_size;
        if (is_power_of_2(block_size))
                c->sectors_per_block_bits = __ffs(block_size) - SECTOR_SHIFT;
        else
                c->sectors_per_block_bits = -1;

        c->alloc_callback = alloc_callback;
        c->write_callback = write_callback;

        if (flags & DM_BUFIO_CLIENT_NO_SLEEP) {
                c->no_sleep = true;
                static_branch_inc(&no_sleep_enabled);
        }

        mutex_init(&c->lock);
        spin_lock_init(&c->spinlock);
        INIT_LIST_HEAD(&c->reserved_buffers);
        c->need_reserved_buffers = reserved_buffers;

        dm_bufio_set_minimum_buffers(c, DM_BUFIO_MIN_BUFFERS);

        init_waitqueue_head(&c->free_buffer_wait);
        c->async_write_error = 0;

        c->dm_io = dm_io_client_create();
        if (IS_ERR(c->dm_io)) {
                r = PTR_ERR(c->dm_io);
                goto bad_dm_io;
        }

        if (block_size <= KMALLOC_MAX_SIZE && !is_power_of_2(block_size)) {
                unsigned int align = min(1U << __ffs(block_size), (unsigned int)PAGE_SIZE);

                snprintf(slab_name, sizeof(slab_name), "dm_bufio_cache-%u-%u",
                                        block_size, atomic_inc_return(&seqno));
                c->slab_cache = kmem_cache_create(slab_name, block_size, align,
                                                  SLAB_RECLAIM_ACCOUNT, NULL);
                if (!c->slab_cache) {
                        r = -ENOMEM;
                        goto bad;
                }
        }
        if (aux_size)
                snprintf(slab_name, sizeof(slab_name), "dm_bufio_buffer-%u-%u",
                                        aux_size, atomic_inc_return(&seqno));
        else
                snprintf(slab_name, sizeof(slab_name), "dm_bufio_buffer-%u",
                                        atomic_inc_return(&seqno));
        c->slab_buffer = kmem_cache_create(slab_name, sizeof(struct dm_buffer) + aux_size,
                                           0, SLAB_RECLAIM_ACCOUNT, NULL);
        if (!c->slab_buffer) {
                r = -ENOMEM;
                goto bad;
        }

        while (c->need_reserved_buffers) {
                struct dm_buffer *b = alloc_buffer(c, GFP_KERNEL);

                if (!b) {
                        r = -ENOMEM;
                        goto bad;
                }
                __free_buffer_wake(b);
        }

        INIT_WORK(&c->shrink_work, shrink_work);
        atomic_long_set(&c->need_shrink, 0);

        c->shrinker = shrinker_alloc(0, "dm-bufio:(%u:%u)",
                                     MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
        if (!c->shrinker) {
                r = -ENOMEM;
                goto bad;
        }

        c->shrinker->count_objects = dm_bufio_shrink_count;
        c->shrinker->scan_objects = dm_bufio_shrink_scan;
        c->shrinker->seeks = 1;
        c->shrinker->batch = 0;
        c->shrinker->private_data = c;

        shrinker_register(c->shrinker);

        mutex_lock(&dm_bufio_clients_lock);
        dm_bufio_client_count++;
        list_add(&c->client_list, &dm_bufio_all_clients);
        __cache_size_refresh();
        mutex_unlock(&dm_bufio_clients_lock);

        return c;

bad:
        while (!list_empty(&c->reserved_buffers)) {
                struct dm_buffer *b = list_to_buffer(c->reserved_buffers.next);

                list_del(&b->lru.list);
                free_buffer(b);
        }
        kmem_cache_destroy(c->slab_cache);
        kmem_cache_destroy(c->slab_buffer);
        dm_io_client_destroy(c->dm_io);
bad_dm_io:
        mutex_destroy(&c->lock);
        if (c->no_sleep)
                static_branch_dec(&no_sleep_enabled);
        kfree(c);
bad_client:
        return ERR_PTR(r);
}
EXPORT_SYMBOL_GPL(dm_bufio_client_create);

/*
 * Free the buffering interface.
 * It is required that there are no references on any buffers.
 */
void dm_bufio_client_destroy(struct dm_bufio_client *c)
{
        unsigned int i;

        drop_buffers(c);

        shrinker_free(c->shrinker);
        flush_work(&c->shrink_work);

        mutex_lock(&dm_bufio_clients_lock);

        list_del(&c->client_list);
        dm_bufio_client_count--;
        __cache_size_refresh();

        mutex_unlock(&dm_bufio_clients_lock);

        WARN_ON(c->need_reserved_buffers);

        while (!list_empty(&c->reserved_buffers)) {
                struct dm_buffer *b = list_to_buffer(c->reserved_buffers.next);

                list_del(&b->lru.list);
                free_buffer(b);
        }

        for (i = 0; i < LIST_SIZE; i++)
                if (cache_count(&c->cache, i))
                        DMERR("leaked buffer count %d: %lu", i, cache_count(&c->cache, i));

        for (i = 0; i < LIST_SIZE; i++)
                WARN_ON(cache_count(&c->cache, i));

        cache_destroy(&c->cache);
        kmem_cache_destroy(c->slab_cache);
        kmem_cache_destroy(c->slab_buffer);
        dm_io_client_destroy(c->dm_io);
        mutex_destroy(&c->lock);
        if (c->no_sleep)
                static_branch_dec(&no_sleep_enabled);
        kfree(c);
}
EXPORT_SYMBOL_GPL(dm_bufio_client_destroy);

void dm_bufio_client_reset(struct dm_bufio_client *c)
{
        drop_buffers(c);
        flush_work(&c->shrink_work);
}
EXPORT_SYMBOL_GPL(dm_bufio_client_reset);

void dm_bufio_set_sector_offset(struct dm_bufio_client *c, sector_t start)
{
        c->start = start;
}
EXPORT_SYMBOL_GPL(dm_bufio_set_sector_offset);

/*--------------------------------------------------------------*/

/*
 * Global cleanup tries to evict the oldest buffers from across _all_
 * the clients.  It does this by repeatedly evicting a few buffers from
 * the client that holds the oldest buffer.  It's approximate, but hopefully
 * good enough.
 */
static struct dm_bufio_client *__pop_client(void)
{
        struct list_head *h;

        if (list_empty(&dm_bufio_all_clients))
                return NULL;

        h = dm_bufio_all_clients.next;
        list_del(h);
        return container_of(h, struct dm_bufio_client, client_list);
}

/*
 * Inserts the client in the global client list based on its
 * 'oldest_buffer' field.
 */
static void __insert_client(struct dm_bufio_client *new_client)
{
        struct dm_bufio_client *c;
        struct list_head *h = dm_bufio_all_clients.next;

        while (h != &dm_bufio_all_clients) {
                c = container_of(h, struct dm_bufio_client, client_list);
                if (time_after_eq(c->oldest_buffer, new_client->oldest_buffer))
                        break;
                h = h->next;
        }

        list_add_tail(&new_client->client_list, h);
}

static enum evict_result select_for_evict(struct dm_buffer *b, void *context)
{
        /* In no-sleep mode, we cannot wait on IO. */
        if (static_branch_unlikely(&no_sleep_enabled) && b->c->no_sleep) {
                if (test_bit_acquire(B_READING, &b->state) ||
                    test_bit(B_WRITING, &b->state) ||
                    test_bit(B_DIRTY, &b->state))
                        return ER_DONT_EVICT;
        }
        return ER_EVICT;
}

static unsigned long __evict_a_few(unsigned long nr_buffers)
{
        struct dm_bufio_client *c;
        unsigned long oldest_buffer = jiffies;
        unsigned long last_accessed;
        unsigned long count;
        struct dm_buffer *b;

        c = __pop_client();
        if (!c)
                return 0;

        dm_bufio_lock(c);

        for (count = 0; count < nr_buffers; count++) {
                b = cache_evict(&c->cache, LIST_CLEAN, select_for_evict, NULL);
                if (!b)
                        break;

                last_accessed = READ_ONCE(b->last_accessed);
                if (time_after_eq(oldest_buffer, last_accessed))
                        oldest_buffer = last_accessed;

                __make_buffer_clean(b);
                __free_buffer_wake(b);

                if (need_resched()) {
                        dm_bufio_unlock(c);
                        cond_resched();
                        dm_bufio_lock(c);
                }
        }

        dm_bufio_unlock(c);

        if (count)
                c->oldest_buffer = oldest_buffer;
        __insert_client(c);

        return count;
}

static void check_watermarks(void)
{
        LIST_HEAD(write_list);
        struct dm_bufio_client *c;

        mutex_lock(&dm_bufio_clients_lock);
        list_for_each_entry(c, &dm_bufio_all_clients, client_list) {
                dm_bufio_lock(c);
                __check_watermark(c, &write_list);
                dm_bufio_unlock(c);
        }
        mutex_unlock(&dm_bufio_clients_lock);

        __flush_write_list(&write_list);
}

static void evict_old(void)
{
        unsigned long threshold = dm_bufio_cache_size -
                dm_bufio_cache_size / DM_BUFIO_LOW_WATERMARK_RATIO;

        mutex_lock(&dm_bufio_clients_lock);
        while (dm_bufio_current_allocated > threshold) {
                if (!__evict_a_few(64))
                        break;
                cond_resched();
        }
        mutex_unlock(&dm_bufio_clients_lock);
}

static void do_global_cleanup(struct work_struct *w)
{
        check_watermarks();
        evict_old();
}

/*
 *--------------------------------------------------------------
 * Module setup
 *--------------------------------------------------------------
 */

/*
 * This is called only once for the whole dm_bufio module.
 * It initializes memory limit.
 */
static int __init dm_bufio_init(void)
{
        __u64 mem;

        dm_bufio_allocated_kmem_cache = 0;
        dm_bufio_allocated_kmalloc = 0;
        dm_bufio_allocated_get_free_pages = 0;
        dm_bufio_allocated_vmalloc = 0;
        dm_bufio_current_allocated = 0;

        mem = (__u64)mult_frac(totalram_pages() - totalhigh_pages(),
                               DM_BUFIO_MEMORY_PERCENT, 100) << PAGE_SHIFT;

        if (mem > ULONG_MAX)
                mem = ULONG_MAX;

#ifdef CONFIG_MMU
        if (mem > mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100))
                mem = mult_frac(VMALLOC_TOTAL, DM_BUFIO_VMALLOC_PERCENT, 100);
#endif

        dm_bufio_default_cache_size = mem;

        mutex_lock(&dm_bufio_clients_lock);
        __cache_size_refresh();
        mutex_unlock(&dm_bufio_clients_lock);

        dm_bufio_wq = alloc_workqueue("dm_bufio_cache",
                                      WQ_MEM_RECLAIM | WQ_PERCPU, 0);
        if (!dm_bufio_wq)
                return -ENOMEM;

        INIT_WORK(&dm_bufio_replacement_work, do_global_cleanup);

        return 0;
}

/*
 * This is called once when unloading the dm_bufio module.
 */
static void __exit dm_bufio_exit(void)
{
        int bug = 0;

        destroy_workqueue(dm_bufio_wq);

        if (dm_bufio_client_count) {
                DMCRIT("%s: dm_bufio_client_count leaked: %d",
                        __func__, dm_bufio_client_count);
                bug = 1;
        }

        if (dm_bufio_current_allocated) {
                DMCRIT("%s: dm_bufio_current_allocated leaked: %lu",
                        __func__, dm_bufio_current_allocated);
                bug = 1;
        }

        if (dm_bufio_allocated_get_free_pages) {
                DMCRIT("%s: dm_bufio_allocated_get_free_pages leaked: %lu",
                       __func__, dm_bufio_allocated_get_free_pages);
                bug = 1;
        }

        if (dm_bufio_allocated_vmalloc) {
                DMCRIT("%s: dm_bufio_vmalloc leaked: %lu",
                       __func__, dm_bufio_allocated_vmalloc);
                bug = 1;
        }

        WARN_ON(bug); /* leaks are not worth crashing the system */
}

module_init(dm_bufio_init)
module_exit(dm_bufio_exit)

module_param_named(max_cache_size_bytes, dm_bufio_cache_size, ulong, 0644);
MODULE_PARM_DESC(max_cache_size_bytes, "Size of metadata cache");

module_param_named(max_age_seconds, dm_bufio_max_age, uint, 0644);
MODULE_PARM_DESC(max_age_seconds, "No longer does anything");

module_param_named(retain_bytes, dm_bufio_retain_bytes, ulong, 0644);
MODULE_PARM_DESC(retain_bytes, "Try to keep at least this many bytes cached in memory");

module_param_named(peak_allocated_bytes, dm_bufio_peak_allocated, ulong, 0644);
MODULE_PARM_DESC(peak_allocated_bytes, "Tracks the maximum allocated memory");

module_param_named(allocated_kmem_cache_bytes, dm_bufio_allocated_kmem_cache, ulong, 0444);
MODULE_PARM_DESC(allocated_kmem_cache_bytes, "Memory allocated with kmem_cache_alloc");

module_param_named(allocated_kmalloc_bytes, dm_bufio_allocated_kmalloc, ulong, 0444);
MODULE_PARM_DESC(allocated_kmalloc_bytes, "Memory allocated with kmalloc_alloc");

module_param_named(allocated_get_free_pages_bytes, dm_bufio_allocated_get_free_pages, ulong, 0444);
MODULE_PARM_DESC(allocated_get_free_pages_bytes, "Memory allocated with get_free_pages");

module_param_named(allocated_vmalloc_bytes, dm_bufio_allocated_vmalloc, ulong, 0444);
MODULE_PARM_DESC(allocated_vmalloc_bytes, "Memory allocated with vmalloc");

module_param_named(current_allocated_bytes, dm_bufio_current_allocated, ulong, 0444);
MODULE_PARM_DESC(current_allocated_bytes, "Memory currently used by the cache");

MODULE_AUTHOR("Mikulas Patocka <dm-devel@lists.linux.dev>");
MODULE_DESCRIPTION(DM_NAME " buffered I/O library");
MODULE_LICENSE("GPL");