// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright 2023-2024 Intel Corporation (Maarten Lankhorst <dev@lankhorst.se>)
 * Copyright 2024 Red Hat (Maxime Ripard <mripard@kernel.org>)
 * Partially based on the rdma and misc controllers, which bear the following copyrights:
 *
 * Copyright 2020 Google LLC
 * Copyright (C) 2016 Parav Pandit <pandit.parav@gmail.com>
 */

#include <linux/cgroup.h>
#include <linux/cgroup_dmem.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/page_counter.h>
#include <linux/parser.h>
#include <linux/refcount.h>
#include <linux/rculist.h>
#include <linux/slab.h>

struct dmem_cgroup_region {
        /**
         * @ref: References keeping the region alive.
         * Keeps the region reference alive after a succesful RCU lookup.
         */
        struct kref ref;

        /** @rcu: RCU head for freeing */
        struct rcu_head rcu;

        /**
         * @region_node: Linked into &dmem_cgroup_regions list.
         * Protected by RCU and global spinlock.
         */
        struct list_head region_node;

        /**
         * @pools: List of pools linked to this region.
         * Protected by global spinlock only
         */
        struct list_head pools;

        /** @size: Size of region, in bytes */
        u64 size;

        /** @name: Name describing the node, set by dmem_cgroup_register_region */
        char *name;

        /**
         * @unregistered: Whether the region is unregistered by its caller.
         * No new pools should be added to the region afterwards.
         */
        bool unregistered;
};

struct dmemcg_state {
        struct cgroup_subsys_state css;

        struct list_head pools;
};

struct dmem_cgroup_pool_state {
        struct dmem_cgroup_region *region;
        struct dmemcg_state *cs;

        /* css node, RCU protected against region teardown */
        struct list_head        css_node;

        /* dev node, no RCU protection required */
        struct list_head        region_node;

        struct rcu_head rcu;

        struct page_counter cnt;
        struct dmem_cgroup_pool_state *parent;

        refcount_t ref;
        bool inited;
};

/*
 * 3 operations require locking protection:
 * - Registering and unregistering region to/from list, requires global lock.
 * - Adding a dmem_cgroup_pool_state to a CSS, removing when CSS is freed.
 * - Adding a dmem_cgroup_pool_state to a region list.
 *
 * Since for the most common operations RCU provides enough protection, I
 * do not think more granular locking makes sense. Most protection is offered
 * by RCU and the lockless operating page_counter.
 */
static DEFINE_SPINLOCK(dmemcg_lock);
static LIST_HEAD(dmem_cgroup_regions);

static void dmemcg_free_region(struct kref *ref);
static void dmemcg_pool_free_rcu(struct rcu_head *rcu);

static inline struct dmemcg_state *
css_to_dmemcs(struct cgroup_subsys_state *css)
{
        return container_of(css, struct dmemcg_state, css);
}

static inline struct dmemcg_state *get_current_dmemcs(void)
{
        return css_to_dmemcs(task_get_css(current, dmem_cgrp_id));
}

static struct dmemcg_state *parent_dmemcs(struct dmemcg_state *cg)
{
        return cg->css.parent ? css_to_dmemcs(cg->css.parent) : NULL;
}

static void dmemcg_pool_get(struct dmem_cgroup_pool_state *pool)
{
        refcount_inc(&pool->ref);
}

static bool dmemcg_pool_tryget(struct dmem_cgroup_pool_state *pool)
{
        return refcount_inc_not_zero(&pool->ref);
}

static void dmemcg_pool_put(struct dmem_cgroup_pool_state *pool)
{
        if (!refcount_dec_and_test(&pool->ref))
                return;

        call_rcu(&pool->rcu, dmemcg_pool_free_rcu);
}

static void dmemcg_pool_free_rcu(struct rcu_head *rcu)
{
        struct dmem_cgroup_pool_state *pool = container_of(rcu, typeof(*pool), rcu);

        if (pool->parent)
                dmemcg_pool_put(pool->parent);
        kref_put(&pool->region->ref, dmemcg_free_region);
        kfree(pool);
}

static void free_cg_pool(struct dmem_cgroup_pool_state *pool)
{
        list_del(&pool->region_node);
        dmemcg_pool_put(pool);
}

static void
set_resource_min(struct dmem_cgroup_pool_state *pool, u64 val)
{
        page_counter_set_min(&pool->cnt, val);
}

static void
set_resource_low(struct dmem_cgroup_pool_state *pool, u64 val)
{
        page_counter_set_low(&pool->cnt, val);
}

static void
set_resource_max(struct dmem_cgroup_pool_state *pool, u64 val)
{
        page_counter_set_max(&pool->cnt, val);
}

static u64 get_resource_low(struct dmem_cgroup_pool_state *pool)
{
        return pool ? READ_ONCE(pool->cnt.low) : 0;
}

static u64 get_resource_min(struct dmem_cgroup_pool_state *pool)
{
        return pool ? READ_ONCE(pool->cnt.min) : 0;
}

static u64 get_resource_max(struct dmem_cgroup_pool_state *pool)
{
        return pool ? READ_ONCE(pool->cnt.max) : PAGE_COUNTER_MAX;
}

static u64 get_resource_current(struct dmem_cgroup_pool_state *pool)
{
        return pool ? page_counter_read(&pool->cnt) : 0;
}

static void reset_all_resource_limits(struct dmem_cgroup_pool_state *rpool)
{
        set_resource_min(rpool, 0);
        set_resource_low(rpool, 0);
        set_resource_max(rpool, PAGE_COUNTER_MAX);
}

static void dmemcs_offline(struct cgroup_subsys_state *css)
{
        struct dmemcg_state *dmemcs = css_to_dmemcs(css);
        struct dmem_cgroup_pool_state *pool;

        rcu_read_lock();
        list_for_each_entry_rcu(pool, &dmemcs->pools, css_node)
                reset_all_resource_limits(pool);
        rcu_read_unlock();
}

static void dmemcs_free(struct cgroup_subsys_state *css)
{
        struct dmemcg_state *dmemcs = css_to_dmemcs(css);
        struct dmem_cgroup_pool_state *pool, *next;

        spin_lock(&dmemcg_lock);
        list_for_each_entry_safe(pool, next, &dmemcs->pools, css_node) {
                /*
                 *The pool is dead and all references are 0,
                 * no need for RCU protection with list_del_rcu or freeing.
                 */
                list_del(&pool->css_node);
                free_cg_pool(pool);
        }
        spin_unlock(&dmemcg_lock);

        kfree(dmemcs);
}

static struct cgroup_subsys_state *
dmemcs_alloc(struct cgroup_subsys_state *parent_css)
{
        struct dmemcg_state *dmemcs = kzalloc_obj(*dmemcs);
        if (!dmemcs)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&dmemcs->pools);
        return &dmemcs->css;
}

static struct dmem_cgroup_pool_state *
find_cg_pool_locked(struct dmemcg_state *dmemcs, struct dmem_cgroup_region *region)
{
        struct dmem_cgroup_pool_state *pool;

        list_for_each_entry_rcu(pool, &dmemcs->pools, css_node, spin_is_locked(&dmemcg_lock))
                if (pool->region == region)
                        return pool;

        return NULL;
}

static struct dmem_cgroup_pool_state *pool_parent(struct dmem_cgroup_pool_state *pool)
{
        if (!pool->cnt.parent)
                return NULL;

        return container_of(pool->cnt.parent, typeof(*pool), cnt);
}

static void
dmem_cgroup_calculate_protection(struct dmem_cgroup_pool_state *limit_pool,
                                 struct dmem_cgroup_pool_state *test_pool)
{
        struct page_counter *climit;
        struct cgroup_subsys_state *css;
        struct dmemcg_state *dmemcg_iter;
        struct dmem_cgroup_pool_state *pool, *found_pool;

        climit = &limit_pool->cnt;

        rcu_read_lock();

        css_for_each_descendant_pre(css, &limit_pool->cs->css) {
                dmemcg_iter = container_of(css, struct dmemcg_state, css);
                found_pool = NULL;

                list_for_each_entry_rcu(pool, &dmemcg_iter->pools, css_node) {
                        if (pool->region == limit_pool->region) {
                                found_pool = pool;
                                break;
                        }
                }
                if (!found_pool)
                        continue;

                page_counter_calculate_protection(
                        climit, &found_pool->cnt, true);

                if (found_pool == test_pool)
                        break;
        }
        rcu_read_unlock();
}

/**
 * dmem_cgroup_state_evict_valuable() - Check if we should evict from test_pool
 * @limit_pool: The pool for which we hit limits
 * @test_pool: The pool for which to test
 * @ignore_low: Whether we have to respect low watermarks.
 * @ret_hit_low: Pointer to whether it makes sense to consider low watermark.
 *
 * This function returns true if we can evict from @test_pool, false if not.
 * When returning false and @ignore_low is false, @ret_hit_low may
 * be set to true to indicate this function can be retried with @ignore_low
 * set to true.
 *
 * Return: bool
 */
bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
                                      struct dmem_cgroup_pool_state *test_pool,
                                      bool ignore_low, bool *ret_hit_low)
{
        struct dmem_cgroup_pool_state *pool = test_pool;
        struct page_counter *ctest;
        u64 used, min, low;

        /* Can always evict from current pool, despite limits */
        if (limit_pool == test_pool)
                return true;

        if (limit_pool) {
                if (!parent_dmemcs(limit_pool->cs))
                        return true;

                for (pool = test_pool; pool && limit_pool != pool; pool = pool_parent(pool))
                        {}

                if (!pool)
                        return false;
        } else {
                /*
                 * If there is no cgroup limiting memory usage, use the root
                 * cgroup instead for limit calculations.
                 */
                for (limit_pool = test_pool; pool_parent(limit_pool); limit_pool = pool_parent(limit_pool))
                        {}
        }

        ctest = &test_pool->cnt;

        dmem_cgroup_calculate_protection(limit_pool, test_pool);

        used = page_counter_read(ctest);
        min = READ_ONCE(ctest->emin);

        if (used <= min)
                return false;

        if (!ignore_low) {
                low = READ_ONCE(ctest->elow);
                if (used > low)
                        return true;

                *ret_hit_low = true;
                return false;
        }
        return true;
}
EXPORT_SYMBOL_GPL(dmem_cgroup_state_evict_valuable);

static struct dmem_cgroup_pool_state *
alloc_pool_single(struct dmemcg_state *dmemcs, struct dmem_cgroup_region *region,
                  struct dmem_cgroup_pool_state **allocpool)
{
        struct dmemcg_state *parent = parent_dmemcs(dmemcs);
        struct dmem_cgroup_pool_state *pool, *ppool = NULL;

        if (!*allocpool) {
                pool = kzalloc_obj(*pool, GFP_NOWAIT);
                if (!pool)
                        return ERR_PTR(-ENOMEM);
        } else {
                pool = *allocpool;
                *allocpool = NULL;
        }

        pool->region = region;
        pool->cs = dmemcs;

        if (parent)
                ppool = find_cg_pool_locked(parent, region);

        page_counter_init(&pool->cnt,
                          ppool ? &ppool->cnt : NULL, true);
        reset_all_resource_limits(pool);
        refcount_set(&pool->ref, 1);
        kref_get(&region->ref);
        if (ppool && !pool->parent) {
                pool->parent = ppool;
                dmemcg_pool_get(ppool);
        }

        list_add_tail_rcu(&pool->css_node, &dmemcs->pools);
        list_add_tail(&pool->region_node, &region->pools);

        if (!parent)
                pool->inited = true;
        else
                pool->inited = ppool ? ppool->inited : false;
        return pool;
}

static struct dmem_cgroup_pool_state *
get_cg_pool_locked(struct dmemcg_state *dmemcs, struct dmem_cgroup_region *region,
                   struct dmem_cgroup_pool_state **allocpool)
{
        struct dmem_cgroup_pool_state *pool, *ppool, *retpool;
        struct dmemcg_state *p, *pp;

        /*
         * Recursively create pool, we may not initialize yet on
         * recursion, this is done as a separate step.
         */
        for (p = dmemcs; p; p = parent_dmemcs(p)) {
                pool = find_cg_pool_locked(p, region);
                if (!pool)
                        pool = alloc_pool_single(p, region, allocpool);

                if (IS_ERR(pool))
                        return pool;

                if (p == dmemcs && pool->inited)
                        return pool;

                if (pool->inited)
                        break;
        }

        retpool = pool = find_cg_pool_locked(dmemcs, region);
        for (p = dmemcs, pp = parent_dmemcs(dmemcs); pp; p = pp, pp = parent_dmemcs(p)) {
                if (pool->inited)
                        break;

                /* ppool was created if it didn't exist by above loop. */
                ppool = find_cg_pool_locked(pp, region);

                /* Fix up parent links, mark as inited. */
                pool->cnt.parent = &ppool->cnt;
                if (ppool && !pool->parent) {
                        pool->parent = ppool;
                        dmemcg_pool_get(ppool);
                }
                pool->inited = true;

                pool = ppool;
        }

        return retpool;
}

static void dmemcg_free_rcu(struct rcu_head *rcu)
{
        struct dmem_cgroup_region *region = container_of(rcu, typeof(*region), rcu);
        struct dmem_cgroup_pool_state *pool, *next;

        list_for_each_entry_safe(pool, next, &region->pools, region_node)
                free_cg_pool(pool);
        kfree(region->name);
        kfree(region);
}

static void dmemcg_free_region(struct kref *ref)
{
        struct dmem_cgroup_region *cgregion = container_of(ref, typeof(*cgregion), ref);

        call_rcu(&cgregion->rcu, dmemcg_free_rcu);
}

/**
 * dmem_cgroup_unregister_region() - Unregister a previously registered region.
 * @region: The region to unregister.
 *
 * This function undoes dmem_cgroup_register_region.
 */
void dmem_cgroup_unregister_region(struct dmem_cgroup_region *region)
{
        struct dmem_cgroup_pool_state *pool, *next;

        if (!region)
                return;

        spin_lock(&dmemcg_lock);

        /* Remove from global region list */
        list_del_rcu(&region->region_node);

        list_for_each_entry_safe(pool, next, &region->pools, region_node) {
                list_del_rcu(&pool->css_node);
                list_del(&pool->region_node);
                dmemcg_pool_put(pool);
        }

        /*
         * Ensure any RCU based lookups fail. Additionally,
         * no new pools should be added to the dead region
         * by get_cg_pool_unlocked.
         */
        region->unregistered = true;
        spin_unlock(&dmemcg_lock);

        kref_put(&region->ref, dmemcg_free_region);
}
EXPORT_SYMBOL_GPL(dmem_cgroup_unregister_region);

/**
 * dmem_cgroup_register_region() - Register a regions for dev cgroup.
 * @size: Size of region to register, in bytes.
 * @fmt: Region parameters to register
 *
 * This function registers a node in the dmem cgroup with the
 * name given. After calling this function, the region can be
 * used for allocations.
 *
 * Return: NULL or a struct on success, PTR_ERR on failure.
 */
struct dmem_cgroup_region *dmem_cgroup_register_region(u64 size, const char *fmt, ...)
{
        struct dmem_cgroup_region *ret;
        char *region_name;
        va_list ap;

        if (!size)
                return NULL;

        va_start(ap, fmt);
        region_name = kvasprintf(GFP_KERNEL, fmt, ap);
        va_end(ap);
        if (!region_name)
                return ERR_PTR(-ENOMEM);

        ret = kzalloc_obj(*ret);
        if (!ret) {
                kfree(region_name);
                return ERR_PTR(-ENOMEM);
        }

        INIT_LIST_HEAD(&ret->pools);
        ret->name = region_name;
        ret->size = size;
        kref_init(&ret->ref);

        spin_lock(&dmemcg_lock);
        list_add_tail_rcu(&ret->region_node, &dmem_cgroup_regions);
        spin_unlock(&dmemcg_lock);

        return ret;
}
EXPORT_SYMBOL_GPL(dmem_cgroup_register_region);

static struct dmem_cgroup_region *dmemcg_get_region_by_name(const char *name)
{
        struct dmem_cgroup_region *region;

        list_for_each_entry_rcu(region, &dmem_cgroup_regions, region_node, spin_is_locked(&dmemcg_lock))
                if (!strcmp(name, region->name) &&
                    kref_get_unless_zero(&region->ref))
                        return region;

        return NULL;
}

/**
 * dmem_cgroup_pool_state_put() - Drop a reference to a dmem_cgroup_pool_state
 * @pool: &dmem_cgroup_pool_state
 *
 * Called to drop a reference to the limiting pool returned by
 * dmem_cgroup_try_charge().
 */
void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool)
{
        if (pool) {
                css_put(&pool->cs->css);
                dmemcg_pool_put(pool);
        }
}
EXPORT_SYMBOL_GPL(dmem_cgroup_pool_state_put);

static struct dmem_cgroup_pool_state *
get_cg_pool_unlocked(struct dmemcg_state *cg, struct dmem_cgroup_region *region)
{
        struct dmem_cgroup_pool_state *pool, *allocpool = NULL;

        /* fastpath lookup? */
        rcu_read_lock();
        pool = find_cg_pool_locked(cg, region);
        if (pool && !READ_ONCE(pool->inited))
                pool = NULL;
        if (pool && !dmemcg_pool_tryget(pool))
                pool = NULL;
        rcu_read_unlock();

        while (!pool) {
                spin_lock(&dmemcg_lock);
                if (!region->unregistered)
                        pool = get_cg_pool_locked(cg, region, &allocpool);
                else
                        pool = ERR_PTR(-ENODEV);
                if (!IS_ERR(pool))
                        dmemcg_pool_get(pool);
                spin_unlock(&dmemcg_lock);

                if (pool == ERR_PTR(-ENOMEM)) {
                        pool = NULL;
                        if (WARN_ON(allocpool))
                                continue;

                        allocpool = kzalloc_obj(*allocpool);
                        if (allocpool) {
                                pool = NULL;
                                continue;
                        }
                }
        }

        kfree(allocpool);
        return pool;
}

/**
 * dmem_cgroup_uncharge() - Uncharge a pool.
 * @pool: Pool to uncharge.
 * @size: Size to uncharge.
 *
 * Undoes the effects of dmem_cgroup_try_charge.
 * Must be called with the returned pool as argument,
 * and same @index and @size.
 */
void dmem_cgroup_uncharge(struct dmem_cgroup_pool_state *pool, u64 size)
{
        if (!pool)
                return;

        page_counter_uncharge(&pool->cnt, size);
        css_put(&pool->cs->css);
        dmemcg_pool_put(pool);
}
EXPORT_SYMBOL_GPL(dmem_cgroup_uncharge);

/**
 * dmem_cgroup_try_charge() - Try charging a new allocation to a region.
 * @region: dmem region to charge
 * @size: Size (in bytes) to charge.
 * @ret_pool: On succesfull allocation, the pool that is charged.
 * @ret_limit_pool: On a failed allocation, the limiting pool.
 *
 * This function charges the @region region for a size of @size bytes.
 *
 * If the function succeeds, @ret_pool is set, which must be passed to
 * dmem_cgroup_uncharge() when undoing the allocation.
 *
 * When this function fails with -EAGAIN and @ret_limit_pool is non-null, it
 * will be set to the pool for which the limit is hit. This can be used for
 * eviction as argument to dmem_cgroup_evict_valuable(). This reference must be freed
 * with @dmem_cgroup_pool_state_put().
 *
 * Return: 0 on success, -EAGAIN on hitting a limit, or a negative errno on failure.
 */
int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size,
                          struct dmem_cgroup_pool_state **ret_pool,
                          struct dmem_cgroup_pool_state **ret_limit_pool)
{
        struct dmemcg_state *cg;
        struct dmem_cgroup_pool_state *pool;
        struct page_counter *fail;
        int ret;

        *ret_pool = NULL;
        if (ret_limit_pool)
                *ret_limit_pool = NULL;

        /*
         * hold on to css, as cgroup can be removed but resource
         * accounting happens on css.
         */
        cg = get_current_dmemcs();

        pool = get_cg_pool_unlocked(cg, region);
        if (IS_ERR(pool)) {
                ret = PTR_ERR(pool);
                goto err;
        }

        if (!page_counter_try_charge(&pool->cnt, size, &fail)) {
                if (ret_limit_pool) {
                        *ret_limit_pool = container_of(fail, struct dmem_cgroup_pool_state, cnt);
                        css_get(&(*ret_limit_pool)->cs->css);
                        dmemcg_pool_get(*ret_limit_pool);
                }
                dmemcg_pool_put(pool);
                ret = -EAGAIN;
                goto err;
        }

        /* On success, reference from get_current_dmemcs is transferred to *ret_pool */
        *ret_pool = pool;
        return 0;

err:
        css_put(&cg->css);
        return ret;
}
EXPORT_SYMBOL_GPL(dmem_cgroup_try_charge);

static int dmem_cgroup_region_capacity_show(struct seq_file *sf, void *v)
{
        struct dmem_cgroup_region *region;

        rcu_read_lock();
        list_for_each_entry_rcu(region, &dmem_cgroup_regions, region_node) {
                seq_puts(sf, region->name);
                seq_printf(sf, " %llu\n", region->size);
        }
        rcu_read_unlock();
        return 0;
}

static int dmemcg_parse_limit(char *options, struct dmem_cgroup_region *region,
                              u64 *new_limit)
{
        char *end;

        if (!strcmp(options, "max")) {
                *new_limit = PAGE_COUNTER_MAX;
                return 0;
        }

        *new_limit = memparse(options, &end);
        if (*end != '\0')
                return -EINVAL;

        return 0;
}

static ssize_t dmemcg_limit_write(struct kernfs_open_file *of,
                                 char *buf, size_t nbytes, loff_t off,
                                 void (*apply)(struct dmem_cgroup_pool_state *, u64))
{
        struct dmemcg_state *dmemcs = css_to_dmemcs(of_css(of));
        int err = 0;

        while (buf && !err) {
                struct dmem_cgroup_pool_state *pool = NULL;
                char *options, *region_name;
                struct dmem_cgroup_region *region;
                u64 new_limit;

                options = buf;
                buf = strchr(buf, '\n');
                if (buf)
                        *buf++ = '\0';

                options = strstrip(options);

                /* eat empty lines */
                if (!options[0])
                        continue;

                region_name = strsep(&options, " \t");
                if (!region_name[0])
                        continue;

                if (!options || !*options)
                        return -EINVAL;

                rcu_read_lock();
                region = dmemcg_get_region_by_name(region_name);
                rcu_read_unlock();

                if (!region)
                        return -EINVAL;

                err = dmemcg_parse_limit(options, region, &new_limit);
                if (err < 0)
                        goto out_put;

                pool = get_cg_pool_unlocked(dmemcs, region);
                if (IS_ERR(pool)) {
                        err = PTR_ERR(pool);
                        goto out_put;
                }

                /* And commit */
                apply(pool, new_limit);
                dmemcg_pool_put(pool);

out_put:
                kref_put(&region->ref, dmemcg_free_region);
        }


        return err ?: nbytes;
}

static int dmemcg_limit_show(struct seq_file *sf, void *v,
                            u64 (*fn)(struct dmem_cgroup_pool_state *))
{
        struct dmemcg_state *dmemcs = css_to_dmemcs(seq_css(sf));
        struct dmem_cgroup_region *region;

        rcu_read_lock();
        list_for_each_entry_rcu(region, &dmem_cgroup_regions, region_node) {
                struct dmem_cgroup_pool_state *pool = find_cg_pool_locked(dmemcs, region);
                u64 val;

                seq_puts(sf, region->name);

                val = fn(pool);
                if (val < PAGE_COUNTER_MAX)
                        seq_printf(sf, " %lld\n", val);
                else
                        seq_puts(sf, " max\n");
        }
        rcu_read_unlock();

        return 0;
}

static int dmem_cgroup_region_current_show(struct seq_file *sf, void *v)
{
        return dmemcg_limit_show(sf, v, get_resource_current);
}

static int dmem_cgroup_region_min_show(struct seq_file *sf, void *v)
{
        return dmemcg_limit_show(sf, v, get_resource_min);
}

static ssize_t dmem_cgroup_region_min_write(struct kernfs_open_file *of,
                                      char *buf, size_t nbytes, loff_t off)
{
        return dmemcg_limit_write(of, buf, nbytes, off, set_resource_min);
}

static int dmem_cgroup_region_low_show(struct seq_file *sf, void *v)
{
        return dmemcg_limit_show(sf, v, get_resource_low);
}

static ssize_t dmem_cgroup_region_low_write(struct kernfs_open_file *of,
                                      char *buf, size_t nbytes, loff_t off)
{
        return dmemcg_limit_write(of, buf, nbytes, off, set_resource_low);
}

static int dmem_cgroup_region_max_show(struct seq_file *sf, void *v)
{
        return dmemcg_limit_show(sf, v, get_resource_max);
}

static ssize_t dmem_cgroup_region_max_write(struct kernfs_open_file *of,
                                      char *buf, size_t nbytes, loff_t off)
{
        return dmemcg_limit_write(of, buf, nbytes, off, set_resource_max);
}

static struct cftype files[] = {
        {
                .name = "capacity",
                .seq_show = dmem_cgroup_region_capacity_show,
                .flags = CFTYPE_ONLY_ON_ROOT,
        },
        {
                .name = "current",
                .seq_show = dmem_cgroup_region_current_show,
        },
        {
                .name = "min",
                .write = dmem_cgroup_region_min_write,
                .seq_show = dmem_cgroup_region_min_show,
                .flags = CFTYPE_NOT_ON_ROOT,
        },
        {
                .name = "low",
                .write = dmem_cgroup_region_low_write,
                .seq_show = dmem_cgroup_region_low_show,
                .flags = CFTYPE_NOT_ON_ROOT,
        },
        {
                .name = "max",
                .write = dmem_cgroup_region_max_write,
                .seq_show = dmem_cgroup_region_max_show,
                .flags = CFTYPE_NOT_ON_ROOT,
        },
        { } /* Zero entry terminates. */
};

struct cgroup_subsys dmem_cgrp_subsys = {
        .css_alloc      = dmemcs_alloc,
        .css_free       = dmemcs_free,
        .css_offline    = dmemcs_offline,
        .legacy_cftypes = files,
        .dfl_cftypes    = files,
};