// SPDX-License-Identifier: GPL-2.0
/*
 *  linux/mm/swap_state.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 *
 *  Rewritten to use page cache, (C) 1998 Stephen Tweedie
 */
#include <linux/mm.h>
#include <linux/gfp.h>
#include <linux/kernel_stat.h>
#include <linux/mempolicy.h>
#include <linux/swap.h>
#include <linux/leafops.h>
#include <linux/init.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/backing-dev.h>
#include <linux/blkdev.h>
#include <linux/migrate.h>
#include <linux/vmalloc.h>
#include <linux/huge_mm.h>
#include <linux/shmem_fs.h>
#include "internal.h"
#include "swap_table.h"
#include "swap.h"

/*
 * swapper_space is a fiction, retained to simplify the path through
 * vmscan's shrink_folio_list.
 */
static const struct address_space_operations swap_aops = {
        .dirty_folio    = noop_dirty_folio,
#ifdef CONFIG_MIGRATION
        .migrate_folio  = migrate_folio,
#endif
};

struct address_space swap_space __read_mostly = {
        .a_ops = &swap_aops,
};

static bool enable_vma_readahead __read_mostly = true;

#define SWAP_RA_ORDER_CEILING   5

#define SWAP_RA_WIN_SHIFT       (PAGE_SHIFT / 2)
#define SWAP_RA_HITS_MASK       ((1UL << SWAP_RA_WIN_SHIFT) - 1)
#define SWAP_RA_HITS_MAX        SWAP_RA_HITS_MASK
#define SWAP_RA_WIN_MASK        (~PAGE_MASK & ~SWAP_RA_HITS_MASK)

#define SWAP_RA_HITS(v)         ((v) & SWAP_RA_HITS_MASK)
#define SWAP_RA_WIN(v)          (((v) & SWAP_RA_WIN_MASK) >> SWAP_RA_WIN_SHIFT)
#define SWAP_RA_ADDR(v)         ((v) & PAGE_MASK)

#define SWAP_RA_VAL(addr, win, hits)                            \
        (((addr) & PAGE_MASK) |                                 \
         (((win) << SWAP_RA_WIN_SHIFT) & SWAP_RA_WIN_MASK) |    \
         ((hits) & SWAP_RA_HITS_MASK))

/* Initial readahead hits is 4 to start up with a small window */
#define GET_SWAP_RA_VAL(vma)                                    \
        (atomic_long_read(&(vma)->swap_readahead_info) ? : 4)

static atomic_t swapin_readahead_hits = ATOMIC_INIT(4);

void show_swap_cache_info(void)
{
        printk("%lu pages in swap cache\n", total_swapcache_pages());
        printk("Free swap  = %ldkB\n", K(get_nr_swap_pages()));
        printk("Total swap = %lukB\n", K(total_swap_pages));
}

/**
 * swap_cache_get_folio - Looks up a folio in the swap cache.
 * @entry: swap entry used for the lookup.
 *
 * A found folio will be returned unlocked and with its refcount increased.
 *
 * Context: Caller must ensure @entry is valid and protect the swap device
 * with reference count or locks.
 * Return: Returns the found folio on success, NULL otherwise. The caller
 * must lock and check if the folio still matches the swap entry before
 * use (e.g., folio_matches_swap_entry).
 */
struct folio *swap_cache_get_folio(swp_entry_t entry)
{
        unsigned long swp_tb;
        struct folio *folio;

        for (;;) {
                swp_tb = swap_table_get(__swap_entry_to_cluster(entry),
                                        swp_cluster_offset(entry));
                if (!swp_tb_is_folio(swp_tb))
                        return NULL;
                folio = swp_tb_to_folio(swp_tb);
                if (likely(folio_try_get(folio)))
                        return folio;
        }

        return NULL;
}

/**
 * swap_cache_has_folio - Check if a swap slot has cache.
 * @entry: swap entry indicating the slot.
 *
 * Context: Caller must ensure @entry is valid and protect the swap
 * device with reference count or locks.
 */
bool swap_cache_has_folio(swp_entry_t entry)
{
        unsigned long swp_tb;

        swp_tb = swap_table_get(__swap_entry_to_cluster(entry),
                                swp_cluster_offset(entry));
        return swp_tb_is_folio(swp_tb);
}

/**
 * swap_cache_get_shadow - Looks up a shadow in the swap cache.
 * @entry: swap entry used for the lookup.
 *
 * Context: Caller must ensure @entry is valid and protect the swap device
 * with reference count or locks.
 * Return: Returns either NULL or an XA_VALUE (shadow).
 */
void *swap_cache_get_shadow(swp_entry_t entry)
{
        unsigned long swp_tb;

        swp_tb = swap_table_get(__swap_entry_to_cluster(entry),
                                swp_cluster_offset(entry));
        if (swp_tb_is_shadow(swp_tb))
                return swp_tb_to_shadow(swp_tb);
        return NULL;
}

void __swap_cache_add_folio(struct swap_cluster_info *ci,
                            struct folio *folio, swp_entry_t entry)
{
        unsigned long new_tb;
        unsigned int ci_start, ci_off, ci_end;
        unsigned long nr_pages = folio_nr_pages(folio);

        VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
        VM_WARN_ON_ONCE_FOLIO(folio_test_swapcache(folio), folio);
        VM_WARN_ON_ONCE_FOLIO(!folio_test_swapbacked(folio), folio);

        new_tb = folio_to_swp_tb(folio);
        ci_start = swp_cluster_offset(entry);
        ci_off = ci_start;
        ci_end = ci_start + nr_pages;
        do {
                VM_WARN_ON_ONCE(swp_tb_is_folio(__swap_table_get(ci, ci_off)));
                __swap_table_set(ci, ci_off, new_tb);
        } while (++ci_off < ci_end);

        folio_ref_add(folio, nr_pages);
        folio_set_swapcache(folio);
        folio->swap = entry;

        node_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages);
        lruvec_stat_mod_folio(folio, NR_SWAPCACHE, nr_pages);
}

/**
 * swap_cache_add_folio - Add a folio into the swap cache.
 * @folio: The folio to be added.
 * @entry: The swap entry corresponding to the folio.
 * @gfp: gfp_mask for XArray node allocation.
 * @shadowp: If a shadow is found, return the shadow.
 *
 * Context: Caller must ensure @entry is valid and protect the swap device
 * with reference count or locks.
 */
static int swap_cache_add_folio(struct folio *folio, swp_entry_t entry,
                                void **shadowp)
{
        int err;
        void *shadow = NULL;
        unsigned long old_tb;
        struct swap_info_struct *si;
        struct swap_cluster_info *ci;
        unsigned int ci_start, ci_off, ci_end, offset;
        unsigned long nr_pages = folio_nr_pages(folio);

        si = __swap_entry_to_info(entry);
        ci_start = swp_cluster_offset(entry);
        ci_end = ci_start + nr_pages;
        ci_off = ci_start;
        offset = swp_offset(entry);
        ci = swap_cluster_lock(si, swp_offset(entry));
        if (unlikely(!ci->table)) {
                err = -ENOENT;
                goto failed;
        }
        do {
                old_tb = __swap_table_get(ci, ci_off);
                if (unlikely(swp_tb_is_folio(old_tb))) {
                        err = -EEXIST;
                        goto failed;
                }
                if (unlikely(!__swap_count(swp_entry(swp_type(entry), offset)))) {
                        err = -ENOENT;
                        goto failed;
                }
                if (swp_tb_is_shadow(old_tb))
                        shadow = swp_tb_to_shadow(old_tb);
                offset++;
        } while (++ci_off < ci_end);
        __swap_cache_add_folio(ci, folio, entry);
        swap_cluster_unlock(ci);
        if (shadowp)
                *shadowp = shadow;
        return 0;

failed:
        swap_cluster_unlock(ci);
        return err;
}

/**
 * __swap_cache_del_folio - Removes a folio from the swap cache.
 * @ci: The locked swap cluster.
 * @folio: The folio.
 * @entry: The first swap entry that the folio corresponds to.
 * @shadow: shadow value to be filled in the swap cache.
 *
 * Removes a folio from the swap cache and fills a shadow in place.
 * This won't put the folio's refcount. The caller has to do that.
 *
 * Context: Caller must ensure the folio is locked and in the swap cache
 * using the index of @entry, and lock the cluster that holds the entries.
 */
void __swap_cache_del_folio(struct swap_cluster_info *ci, struct folio *folio,
                            swp_entry_t entry, void *shadow)
{
        struct swap_info_struct *si;
        unsigned long old_tb, new_tb;
        unsigned int ci_start, ci_off, ci_end;
        bool folio_swapped = false, need_free = false;
        unsigned long nr_pages = folio_nr_pages(folio);

        VM_WARN_ON_ONCE(__swap_entry_to_cluster(entry) != ci);
        VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
        VM_WARN_ON_ONCE_FOLIO(!folio_test_swapcache(folio), folio);
        VM_WARN_ON_ONCE_FOLIO(folio_test_writeback(folio), folio);

        si = __swap_entry_to_info(entry);
        new_tb = shadow_swp_to_tb(shadow);
        ci_start = swp_cluster_offset(entry);
        ci_end = ci_start + nr_pages;
        ci_off = ci_start;
        do {
                /* If shadow is NULL, we sets an empty shadow */
                old_tb = __swap_table_xchg(ci, ci_off, new_tb);
                WARN_ON_ONCE(!swp_tb_is_folio(old_tb) ||
                             swp_tb_to_folio(old_tb) != folio);
                if (__swap_count(swp_entry(si->type,
                                 swp_offset(entry) + ci_off - ci_start)))
                        folio_swapped = true;
                else
                        need_free = true;
        } while (++ci_off < ci_end);

        folio->swap.val = 0;
        folio_clear_swapcache(folio);
        node_stat_mod_folio(folio, NR_FILE_PAGES, -nr_pages);
        lruvec_stat_mod_folio(folio, NR_SWAPCACHE, -nr_pages);

        if (!folio_swapped) {
                swap_entries_free(si, ci, swp_offset(entry), nr_pages);
        } else if (need_free) {
                do {
                        if (!__swap_count(entry))
                                swap_entries_free(si, ci, swp_offset(entry), 1);
                        entry.val++;
                } while (--nr_pages);
        }
}

/**
 * swap_cache_del_folio - Removes a folio from the swap cache.
 * @folio: The folio.
 *
 * Same as __swap_cache_del_folio, but handles lock and refcount. The
 * caller must ensure the folio is either clean or has a swap count
 * equal to zero, or it may cause data loss.
 *
 * Context: Caller must ensure the folio is locked and in the swap cache.
 */
void swap_cache_del_folio(struct folio *folio)
{
        struct swap_cluster_info *ci;
        swp_entry_t entry = folio->swap;

        ci = swap_cluster_lock(__swap_entry_to_info(entry), swp_offset(entry));
        __swap_cache_del_folio(ci, folio, entry, NULL);
        swap_cluster_unlock(ci);

        folio_ref_sub(folio, folio_nr_pages(folio));
}

/**
 * __swap_cache_replace_folio - Replace a folio in the swap cache.
 * @ci: The locked swap cluster.
 * @old: The old folio to be replaced.
 * @new: The new folio.
 *
 * Replace an existing folio in the swap cache with a new folio. The
 * caller is responsible for setting up the new folio's flag and swap
 * entries. Replacement will take the new folio's swap entry value as
 * the starting offset to override all slots covered by the new folio.
 *
 * Context: Caller must ensure both folios are locked, and lock the
 * cluster that holds the old folio to be replaced.
 */
void __swap_cache_replace_folio(struct swap_cluster_info *ci,
                                struct folio *old, struct folio *new)
{
        swp_entry_t entry = new->swap;
        unsigned long nr_pages = folio_nr_pages(new);
        unsigned int ci_off = swp_cluster_offset(entry);
        unsigned int ci_end = ci_off + nr_pages;
        unsigned long old_tb, new_tb;

        VM_WARN_ON_ONCE(!folio_test_swapcache(old) || !folio_test_swapcache(new));
        VM_WARN_ON_ONCE(!folio_test_locked(old) || !folio_test_locked(new));
        VM_WARN_ON_ONCE(!entry.val);

        /* Swap cache still stores N entries instead of a high-order entry */
        new_tb = folio_to_swp_tb(new);
        do {
                old_tb = __swap_table_xchg(ci, ci_off, new_tb);
                WARN_ON_ONCE(!swp_tb_is_folio(old_tb) || swp_tb_to_folio(old_tb) != old);
        } while (++ci_off < ci_end);

        /*
         * If the old folio is partially replaced (e.g., splitting a large
         * folio, the old folio is shrunk, and new split sub folios replace
         * the shrunk part), ensure the new folio doesn't overlap it.
         */
        if (IS_ENABLED(CONFIG_DEBUG_VM) &&
            folio_order(old) != folio_order(new)) {
                ci_off = swp_cluster_offset(old->swap);
                ci_end = ci_off + folio_nr_pages(old);
                while (ci_off++ < ci_end)
                        WARN_ON_ONCE(swp_tb_to_folio(__swap_table_get(ci, ci_off)) != old);
        }
}

/**
 * __swap_cache_clear_shadow - Clears a set of shadows in the swap cache.
 * @entry: The starting index entry.
 * @nr_ents: How many slots need to be cleared.
 *
 * Context: Caller must ensure the range is valid, all in one single cluster,
 * not occupied by any folio, and lock the cluster.
 */
void __swap_cache_clear_shadow(swp_entry_t entry, int nr_ents)
{
        struct swap_cluster_info *ci = __swap_entry_to_cluster(entry);
        unsigned int ci_off = swp_cluster_offset(entry), ci_end;
        unsigned long old;

        ci_end = ci_off + nr_ents;
        do {
                old = __swap_table_xchg(ci, ci_off, null_to_swp_tb());
                WARN_ON_ONCE(swp_tb_is_folio(old));
        } while (++ci_off < ci_end);
}

/*
 * If we are the only user, then try to free up the swap cache.
 *
 * Its ok to check the swapcache flag without the folio lock
 * here because we are going to recheck again inside
 * folio_free_swap() _with_ the lock.
 *                                      - Marcelo
 */
void free_swap_cache(struct folio *folio)
{
        if (folio_test_swapcache(folio) && !folio_mapped(folio) &&
            folio_trylock(folio)) {
                folio_free_swap(folio);
                folio_unlock(folio);
        }
}

/*
 * Freeing a folio and also freeing any swap cache associated with
 * this folio if it is the last user.
 */
void free_folio_and_swap_cache(struct folio *folio)
{
        free_swap_cache(folio);
        if (!is_huge_zero_folio(folio))
                folio_put(folio);
}

/*
 * Passed an array of pages, drop them all from swapcache and then release
 * them.  They are removed from the LRU and freed if this is their last use.
 */
void free_pages_and_swap_cache(struct encoded_page **pages, int nr)
{
        struct folio_batch folios;
        unsigned int refs[PAGEVEC_SIZE];

        folio_batch_init(&folios);
        for (int i = 0; i < nr; i++) {
                struct folio *folio = page_folio(encoded_page_ptr(pages[i]));

                free_swap_cache(folio);
                refs[folios.nr] = 1;
                if (unlikely(encoded_page_flags(pages[i]) &
                             ENCODED_PAGE_BIT_NR_PAGES_NEXT))
                        refs[folios.nr] = encoded_nr_pages(pages[++i]);

                if (folio_batch_add(&folios, folio) == 0)
                        folios_put_refs(&folios, refs);
        }
        if (folios.nr)
                folios_put_refs(&folios, refs);
}

static inline bool swap_use_vma_readahead(void)
{
        return READ_ONCE(enable_vma_readahead) && !atomic_read(&nr_rotate_swap);
}

/**
 * swap_update_readahead - Update the readahead statistics of VMA or globally.
 * @folio: the swap cache folio that just got hit.
 * @vma: the VMA that should be updated, could be NULL for global update.
 * @addr: the addr that triggered the swapin, ignored if @vma is NULL.
 */
void swap_update_readahead(struct folio *folio, struct vm_area_struct *vma,
                           unsigned long addr)
{
        bool readahead, vma_ra = swap_use_vma_readahead();

        /*
         * At the moment, we don't support PG_readahead for anon THP
         * so let's bail out rather than confusing the readahead stat.
         */
        if (unlikely(folio_test_large(folio)))
                return;

        readahead = folio_test_clear_readahead(folio);
        if (vma && vma_ra) {
                unsigned long ra_val;
                int win, hits;

                ra_val = GET_SWAP_RA_VAL(vma);
                win = SWAP_RA_WIN(ra_val);
                hits = SWAP_RA_HITS(ra_val);
                if (readahead)
                        hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
                atomic_long_set(&vma->swap_readahead_info,
                                SWAP_RA_VAL(addr, win, hits));
        }

        if (readahead) {
                count_vm_event(SWAP_RA_HIT);
                if (!vma || !vma_ra)
                        atomic_inc(&swapin_readahead_hits);
        }
}

/**
 * __swap_cache_prepare_and_add - Prepare the folio and add it to swap cache.
 * @entry: swap entry to be bound to the folio.
 * @folio: folio to be added.
 * @gfp: memory allocation flags for charge, can be 0 if @charged if true.
 * @charged: if the folio is already charged.
 *
 * Update the swap_map and add folio as swap cache, typically before swapin.
 * All swap slots covered by the folio must have a non-zero swap count.
 *
 * Context: Caller must protect the swap device with reference count or locks.
 * Return: Returns the folio being added on success. Returns the existing folio
 * if @entry is already cached. Returns NULL if raced with swapin or swapoff.
 */
static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
                                                  struct folio *folio,
                                                  gfp_t gfp, bool charged)
{
        struct folio *swapcache = NULL;
        void *shadow;
        int ret;

        __folio_set_locked(folio);
        __folio_set_swapbacked(folio);

        if (!charged && mem_cgroup_swapin_charge_folio(folio, NULL, gfp, entry))
                goto failed;

        for (;;) {
                ret = swap_cache_add_folio(folio, entry, &shadow);
                if (!ret)
                        break;

                /*
                 * Large order allocation needs special handling on
                 * race: if a smaller folio exists in cache, swapin needs
                 * to fallback to order 0, and doing a swap cache lookup
                 * might return a folio that is irrelevant to the faulting
                 * entry because @entry is aligned down. Just return NULL.
                 */
                if (ret != -EEXIST || folio_test_large(folio))
                        goto failed;

                swapcache = swap_cache_get_folio(entry);
                if (swapcache)
                        goto failed;
        }

        memcg1_swapin(entry, folio_nr_pages(folio));
        if (shadow)
                workingset_refault(folio, shadow);

        /* Caller will initiate read into locked folio */
        folio_add_lru(folio);
        return folio;

failed:
        folio_unlock(folio);
        return swapcache;
}

/**
 * swap_cache_alloc_folio - Allocate folio for swapped out slot in swap cache.
 * @entry: the swapped out swap entry to be binded to the folio.
 * @gfp_mask: memory allocation flags
 * @mpol: NUMA memory allocation policy to be applied
 * @ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE
 * @new_page_allocated: sets true if allocation happened, false otherwise
 *
 * Allocate a folio in the swap cache for one swap slot, typically before
 * doing IO (e.g. swap in or zswap writeback). The swap slot indicated by
 * @entry must have a non-zero swap count (swapped out).
 * Currently only supports order 0.
 *
 * Context: Caller must protect the swap device with reference count or locks.
 * Return: Returns the existing folio if @entry is cached already. Returns
 * NULL if failed due to -ENOMEM or @entry have a swap count < 1.
 */
struct folio *swap_cache_alloc_folio(swp_entry_t entry, gfp_t gfp_mask,
                                     struct mempolicy *mpol, pgoff_t ilx,
                                     bool *new_page_allocated)
{
        struct swap_info_struct *si = __swap_entry_to_info(entry);
        struct folio *folio;
        struct folio *result = NULL;

        *new_page_allocated = false;
        /* Check the swap cache again for readahead path. */
        folio = swap_cache_get_folio(entry);
        if (folio)
                return folio;

        /* Skip allocation for unused and bad swap slot for readahead. */
        if (!swap_entry_swapped(si, entry))
                return NULL;

        /* Allocate a new folio to be added into the swap cache. */
        folio = folio_alloc_mpol(gfp_mask, 0, mpol, ilx, numa_node_id());
        if (!folio)
                return NULL;
        /* Try add the new folio, returns existing folio or NULL on failure. */
        result = __swap_cache_prepare_and_add(entry, folio, gfp_mask, false);
        if (result == folio)
                *new_page_allocated = true;
        else
                folio_put(folio);
        return result;
}

/**
 * swapin_folio - swap-in one or multiple entries skipping readahead.
 * @entry: starting swap entry to swap in
 * @folio: a new allocated and charged folio
 *
 * Reads @entry into @folio, @folio will be added to the swap cache.
 * If @folio is a large folio, the @entry will be rounded down to align
 * with the folio size.
 *
 * Return: returns pointer to @folio on success. If folio is a large folio
 * and this raced with another swapin, NULL will be returned to allow fallback
 * to order 0. Else, if another folio was already added to the swap cache,
 * return that swap cache folio instead.
 */
struct folio *swapin_folio(swp_entry_t entry, struct folio *folio)
{
        struct folio *swapcache;
        pgoff_t offset = swp_offset(entry);
        unsigned long nr_pages = folio_nr_pages(folio);

        entry = swp_entry(swp_type(entry), round_down(offset, nr_pages));
        swapcache = __swap_cache_prepare_and_add(entry, folio, 0, true);
        if (swapcache == folio)
                swap_read_folio(folio, NULL);
        return swapcache;
}

/*
 * Locate a page of swap in physical memory, reserving swap cache space
 * and reading the disk if it is not already cached.
 * A failure return means that either the page allocation failed or that
 * the swap entry is no longer in use.
 */
struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                struct vm_area_struct *vma, unsigned long addr,
                struct swap_iocb **plug)
{
        struct swap_info_struct *si;
        bool page_allocated;
        struct mempolicy *mpol;
        pgoff_t ilx;
        struct folio *folio;

        si = get_swap_device(entry);
        if (!si)
                return NULL;

        mpol = get_vma_policy(vma, addr, 0, &ilx);
        folio = swap_cache_alloc_folio(entry, gfp_mask, mpol, ilx,
                                       &page_allocated);
        mpol_cond_put(mpol);

        if (page_allocated)
                swap_read_folio(folio, plug);

        put_swap_device(si);
        return folio;
}

static unsigned int __swapin_nr_pages(unsigned long prev_offset,
                                      unsigned long offset,
                                      int hits,
                                      int max_pages,
                                      int prev_win)
{
        unsigned int pages, last_ra;

        /*
         * This heuristic has been found to work well on both sequential and
         * random loads, swapping to hard disk or to SSD: please don't ask
         * what the "+ 2" means, it just happens to work well, that's all.
         */
        pages = hits + 2;
        if (pages == 2) {
                /*
                 * We can have no readahead hits to judge by: but must not get
                 * stuck here forever, so check for an adjacent offset instead
                 * (and don't even bother to check whether swap type is same).
                 */
                if (offset != prev_offset + 1 && offset != prev_offset - 1)
                        pages = 1;
        } else {
                unsigned int roundup = 4;
                while (roundup < pages)
                        roundup <<= 1;
                pages = roundup;
        }

        if (pages > max_pages)
                pages = max_pages;

        /* Don't shrink readahead too fast */
        last_ra = prev_win / 2;
        if (pages < last_ra)
                pages = last_ra;

        return pages;
}

static unsigned long swapin_nr_pages(unsigned long offset)
{
        static unsigned long prev_offset;
        unsigned int hits, pages, max_pages;
        static atomic_t last_readahead_pages;

        max_pages = 1 << READ_ONCE(page_cluster);
        if (max_pages <= 1)
                return 1;

        hits = atomic_xchg(&swapin_readahead_hits, 0);
        pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
                                  max_pages,
                                  atomic_read(&last_readahead_pages));
        if (!hits)
                WRITE_ONCE(prev_offset, offset);
        atomic_set(&last_readahead_pages, pages);

        return pages;
}

/**
 * swap_cluster_readahead - swap in pages in hope we need them soon
 * @entry: swap entry of this memory
 * @gfp_mask: memory allocation flags
 * @mpol: NUMA memory allocation policy to be applied
 * @ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE
 *
 * Returns the struct folio for entry and addr, after queueing swapin.
 *
 * Primitive swap readahead code. We simply read an aligned block of
 * (1 << page_cluster) entries in the swap area. This method is chosen
 * because it doesn't cost us any seek time.  We also make sure to queue
 * the 'original' request together with the readahead ones...
 *
 * Note: it is intentional that the same NUMA policy and interleave index
 * are used for every page of the readahead: neighbouring pages on swap
 * are fairly likely to have been swapped out from the same node.
 */
struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask,
                                    struct mempolicy *mpol, pgoff_t ilx)
{
        struct folio *folio;
        unsigned long entry_offset = swp_offset(entry);
        unsigned long offset = entry_offset;
        unsigned long start_offset, end_offset;
        unsigned long mask;
        struct swap_info_struct *si = __swap_entry_to_info(entry);
        struct blk_plug plug;
        struct swap_iocb *splug = NULL;
        bool page_allocated;

        mask = swapin_nr_pages(offset) - 1;
        if (!mask)
                goto skip;

        /* Read a page_cluster sized and aligned cluster around offset. */
        start_offset = offset & ~mask;
        end_offset = offset | mask;
        if (!start_offset)      /* First page is swap header. */
                start_offset++;
        if (end_offset >= si->max)
                end_offset = si->max - 1;

        blk_start_plug(&plug);
        for (offset = start_offset; offset <= end_offset ; offset++) {
                /* Ok, do the async read-ahead now */
                folio = swap_cache_alloc_folio(
                        swp_entry(swp_type(entry), offset), gfp_mask, mpol, ilx,
                        &page_allocated);
                if (!folio)
                        continue;
                if (page_allocated) {
                        swap_read_folio(folio, &splug);
                        if (offset != entry_offset) {
                                folio_set_readahead(folio);
                                count_vm_event(SWAP_RA);
                        }
                }
                folio_put(folio);
        }
        blk_finish_plug(&plug);
        swap_read_unplug(splug);
        lru_add_drain();        /* Push any new pages onto the LRU now */
skip:
        /* The page was likely read above, so no need for plugging here */
        folio = swap_cache_alloc_folio(entry, gfp_mask, mpol, ilx,
                                       &page_allocated);
        if (unlikely(page_allocated))
                swap_read_folio(folio, NULL);
        return folio;
}

static int swap_vma_ra_win(struct vm_fault *vmf, unsigned long *start,
                           unsigned long *end)
{
        struct vm_area_struct *vma = vmf->vma;
        unsigned long ra_val;
        unsigned long faddr, prev_faddr, left, right;
        unsigned int max_win, hits, prev_win, win;

        max_win = 1 << min(READ_ONCE(page_cluster), SWAP_RA_ORDER_CEILING);
        if (max_win == 1)
                return 1;

        faddr = vmf->address;
        ra_val = GET_SWAP_RA_VAL(vma);
        prev_faddr = SWAP_RA_ADDR(ra_val);
        prev_win = SWAP_RA_WIN(ra_val);
        hits = SWAP_RA_HITS(ra_val);
        win = __swapin_nr_pages(PFN_DOWN(prev_faddr), PFN_DOWN(faddr), hits,
                                max_win, prev_win);
        atomic_long_set(&vma->swap_readahead_info, SWAP_RA_VAL(faddr, win, 0));
        if (win == 1)
                return 1;

        if (faddr == prev_faddr + PAGE_SIZE)
                left = faddr;
        else if (prev_faddr == faddr + PAGE_SIZE)
                left = faddr - (win << PAGE_SHIFT) + PAGE_SIZE;
        else
                left = faddr - (((win - 1) / 2) << PAGE_SHIFT);
        right = left + (win << PAGE_SHIFT);
        if ((long)left < 0)
                left = 0;
        *start = max3(left, vma->vm_start, faddr & PMD_MASK);
        *end = min3(right, vma->vm_end, (faddr & PMD_MASK) + PMD_SIZE);

        return win;
}

/**
 * swap_vma_readahead - swap in pages in hope we need them soon
 * @targ_entry: swap entry of the targeted memory
 * @gfp_mask: memory allocation flags
 * @mpol: NUMA memory allocation policy to be applied
 * @targ_ilx: NUMA interleave index, for use only when MPOL_INTERLEAVE
 * @vmf: fault information
 *
 * Returns the struct folio for entry and addr, after queueing swapin.
 *
 * Primitive swap readahead code. We simply read in a few pages whose
 * virtual addresses are around the fault address in the same vma.
 *
 * Caller must hold read mmap_lock if vmf->vma is not NULL.
 *
 */
static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
                struct mempolicy *mpol, pgoff_t targ_ilx, struct vm_fault *vmf)
{
        struct blk_plug plug;
        struct swap_iocb *splug = NULL;
        struct folio *folio;
        pte_t *pte = NULL, pentry;
        int win;
        unsigned long start, end, addr;
        pgoff_t ilx;
        bool page_allocated;

        win = swap_vma_ra_win(vmf, &start, &end);
        if (win == 1)
                goto skip;

        ilx = targ_ilx - PFN_DOWN(vmf->address - start);

        blk_start_plug(&plug);
        for (addr = start; addr < end; ilx++, addr += PAGE_SIZE) {
                struct swap_info_struct *si = NULL;
                softleaf_t entry;

                if (!pte++) {
                        pte = pte_offset_map(vmf->pmd, addr);
                        if (!pte)
                                break;
                }
                pentry = ptep_get_lockless(pte);
                entry = softleaf_from_pte(pentry);

                if (!softleaf_is_swap(entry))
                        continue;
                pte_unmap(pte);
                pte = NULL;
                /*
                 * Readahead entry may come from a device that we are not
                 * holding a reference to, try to grab a reference, or skip.
                 */
                if (swp_type(entry) != swp_type(targ_entry)) {
                        si = get_swap_device(entry);
                        if (!si)
                                continue;
                }
                folio = swap_cache_alloc_folio(entry, gfp_mask, mpol, ilx,
                                               &page_allocated);
                if (si)
                        put_swap_device(si);
                if (!folio)
                        continue;
                if (page_allocated) {
                        swap_read_folio(folio, &splug);
                        if (addr != vmf->address) {
                                folio_set_readahead(folio);
                                count_vm_event(SWAP_RA);
                        }
                }
                folio_put(folio);
        }
        if (pte)
                pte_unmap(pte);
        blk_finish_plug(&plug);
        swap_read_unplug(splug);
        lru_add_drain();
skip:
        /* The folio was likely read above, so no need for plugging here */
        folio = swap_cache_alloc_folio(targ_entry, gfp_mask, mpol, targ_ilx,
                                       &page_allocated);
        if (unlikely(page_allocated))
                swap_read_folio(folio, NULL);
        return folio;
}

/**
 * swapin_readahead - swap in pages in hope we need them soon
 * @entry: swap entry of this memory
 * @gfp_mask: memory allocation flags
 * @vmf: fault information
 *
 * Returns the struct folio for entry and addr, after queueing swapin.
 *
 * It's a main entry function for swap readahead. By the configuration,
 * it will read ahead blocks by cluster-based(ie, physical disk based)
 * or vma-based(ie, virtual address based on faulty address) readahead.
 */
struct folio *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
                                struct vm_fault *vmf)
{
        struct mempolicy *mpol;
        pgoff_t ilx;
        struct folio *folio;

        mpol = get_vma_policy(vmf->vma, vmf->address, 0, &ilx);
        folio = swap_use_vma_readahead() ?
                swap_vma_readahead(entry, gfp_mask, mpol, ilx, vmf) :
                swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
        mpol_cond_put(mpol);

        return folio;
}

#ifdef CONFIG_SYSFS
static ssize_t vma_ra_enabled_show(struct kobject *kobj,
                                     struct kobj_attribute *attr, char *buf)
{
        return sysfs_emit(buf, "%s\n", str_true_false(enable_vma_readahead));
}
static ssize_t vma_ra_enabled_store(struct kobject *kobj,
                                      struct kobj_attribute *attr,
                                      const char *buf, size_t count)
{
        ssize_t ret;

        ret = kstrtobool(buf, &enable_vma_readahead);
        if (ret)
                return ret;

        return count;
}
static struct kobj_attribute vma_ra_enabled_attr = __ATTR_RW(vma_ra_enabled);

static struct attribute *swap_attrs[] = {
        &vma_ra_enabled_attr.attr,
        NULL,
};

static const struct attribute_group swap_attr_group = {
        .attrs = swap_attrs,
};

static int __init swap_init(void)
{
        int err;
        struct kobject *swap_kobj;

        swap_kobj = kobject_create_and_add("swap", mm_kobj);
        if (!swap_kobj) {
                pr_err("failed to create swap kobject\n");
                return -ENOMEM;
        }
        err = sysfs_create_group(swap_kobj, &swap_attr_group);
        if (err) {
                pr_err("failed to register swap group\n");
                goto delete_obj;
        }
        /* Swap cache writeback is LRU based, no tags for it */
        mapping_set_no_writeback_tags(&swap_space);
        return 0;

delete_obj:
        kobject_put(swap_kobj);
        return err;
}
subsys_initcall(swap_init);
#endif