// SPDX-License-Identifier: MIT
/*
 * Copyright © 2014-2018 Intel Corporation
 */

#include "gem/i915_gem_object.h"

#include "i915_drv.h"
#include "intel_engine_pm.h"
#include "intel_gt_buffer_pool.h"

static struct intel_gt *to_gt(struct intel_gt_buffer_pool *pool)
{
        return container_of(pool, struct intel_gt, buffer_pool);
}

static struct list_head *
bucket_for_size(struct intel_gt_buffer_pool *pool, size_t sz)
{
        int n;

        /*
         * Compute a power-of-two bucket, but throw everything greater than
         * 16KiB into the same bucket: i.e. the buckets hold objects of
         * (1 page, 2 pages, 4 pages, 8+ pages).
         */
        n = fls(sz >> PAGE_SHIFT) - 1;
        if (n >= ARRAY_SIZE(pool->cache_list))
                n = ARRAY_SIZE(pool->cache_list) - 1;

        return &pool->cache_list[n];
}

static void node_free(struct intel_gt_buffer_pool_node *node)
{
        i915_gem_object_put(node->obj);
        i915_active_fini(&node->active);
        kfree_rcu(node, rcu);
}

static bool pool_free_older_than(struct intel_gt_buffer_pool *pool, long keep)
{
        struct intel_gt_buffer_pool_node *node, *stale = NULL;
        bool active = false;
        int n;

        /* Free buffers that have not been used in the past second */
        for (n = 0; n < ARRAY_SIZE(pool->cache_list); n++) {
                struct list_head *list = &pool->cache_list[n];

                if (list_empty(list))
                        continue;

                if (spin_trylock_irq(&pool->lock)) {
                        struct list_head *pos;

                        /* Most recent at head; oldest at tail */
                        list_for_each_prev(pos, list) {
                                unsigned long age;

                                node = list_entry(pos, typeof(*node), link);

                                age = READ_ONCE(node->age);
                                if (!age || jiffies - age < keep)
                                        break;

                                /* Check we are the first to claim this node */
                                if (!xchg(&node->age, 0))
                                        break;

                                node->free = stale;
                                stale = node;
                        }
                        if (!list_is_last(pos, list))
                                __list_del_many(pos, list);

                        spin_unlock_irq(&pool->lock);
                }

                active |= !list_empty(list);
        }

        while ((node = stale)) {
                stale = stale->free;
                node_free(node);
        }

        return active;
}

static void pool_free_work(struct work_struct *wrk)
{
        struct intel_gt_buffer_pool *pool =
                container_of(wrk, typeof(*pool), work.work);

        if (pool_free_older_than(pool, HZ))
                schedule_delayed_work(&pool->work,
                                      round_jiffies_up_relative(HZ));
}

static void pool_retire(struct i915_active *ref)
{
        struct intel_gt_buffer_pool_node *node =
                container_of(ref, typeof(*node), active);
        struct intel_gt_buffer_pool *pool = node->pool;
        struct list_head *list = bucket_for_size(pool, node->obj->base.size);
        unsigned long flags;

        if (node->pinned) {
                i915_gem_object_unpin_pages(node->obj);

                /* Return this object to the shrinker pool */
                i915_gem_object_make_purgeable(node->obj);
                node->pinned = false;
        }

        GEM_BUG_ON(node->age);
        spin_lock_irqsave(&pool->lock, flags);
        list_add_rcu(&node->link, list);
        WRITE_ONCE(node->age, jiffies ?: 1); /* 0 reserved for active nodes */
        spin_unlock_irqrestore(&pool->lock, flags);

        schedule_delayed_work(&pool->work,
                              round_jiffies_up_relative(HZ));
}

void intel_gt_buffer_pool_mark_used(struct intel_gt_buffer_pool_node *node)
{
        assert_object_held(node->obj);

        if (node->pinned)
                return;

        __i915_gem_object_pin_pages(node->obj);
        /* Hide this pinned object from the shrinker until retired */
        i915_gem_object_make_unshrinkable(node->obj);
        node->pinned = true;
}

static struct intel_gt_buffer_pool_node *
node_create(struct intel_gt_buffer_pool *pool, size_t sz,
            enum i915_map_type type)
{
        struct intel_gt *gt = to_gt(pool);
        struct intel_gt_buffer_pool_node *node;
        struct drm_i915_gem_object *obj;

        node = kmalloc(sizeof(*node),
                       GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
        if (!node)
                return ERR_PTR(-ENOMEM);

        node->age = 0;
        node->pool = pool;
        node->pinned = false;
        i915_active_init(&node->active, NULL, pool_retire, 0);

        obj = i915_gem_object_create_internal(gt->i915, sz);
        if (IS_ERR(obj)) {
                i915_active_fini(&node->active);
                kfree(node);
                return ERR_CAST(obj);
        }

        i915_gem_object_set_readonly(obj);

        node->type = type;
        node->obj = obj;
        return node;
}

struct intel_gt_buffer_pool_node *
intel_gt_get_buffer_pool(struct intel_gt *gt, size_t size,
                         enum i915_map_type type)
{
        struct intel_gt_buffer_pool *pool = &gt->buffer_pool;
        struct intel_gt_buffer_pool_node *node;
        struct list_head *list;
        int ret;

        size = PAGE_ALIGN(size);
        list = bucket_for_size(pool, size);

        rcu_read_lock();
        list_for_each_entry_rcu(node, list, link) {
                unsigned long age;

                if (node->obj->base.size < size)
                        continue;

                if (node->type != type)
                        continue;

                age = READ_ONCE(node->age);
                if (!age)
                        continue;

                if (cmpxchg(&node->age, age, 0) == age) {
                        spin_lock_irq(&pool->lock);
                        list_del_rcu(&node->link);
                        spin_unlock_irq(&pool->lock);
                        break;
                }
        }
        rcu_read_unlock();

        if (&node->link == list) {
                node = node_create(pool, size, type);
                if (IS_ERR(node))
                        return node;
        }

        ret = i915_active_acquire(&node->active);
        if (ret) {
                node_free(node);
                return ERR_PTR(ret);
        }

        return node;
}

void intel_gt_init_buffer_pool(struct intel_gt *gt)
{
        struct intel_gt_buffer_pool *pool = &gt->buffer_pool;
        int n;

        spin_lock_init(&pool->lock);
        for (n = 0; n < ARRAY_SIZE(pool->cache_list); n++)
                INIT_LIST_HEAD(&pool->cache_list[n]);
        INIT_DELAYED_WORK(&pool->work, pool_free_work);
}

void intel_gt_flush_buffer_pool(struct intel_gt *gt)
{
        struct intel_gt_buffer_pool *pool = &gt->buffer_pool;

        do {
                while (pool_free_older_than(pool, 0))
                        ;
        } while (cancel_delayed_work_sync(&pool->work));
}

void intel_gt_fini_buffer_pool(struct intel_gt *gt)
{
        struct intel_gt_buffer_pool *pool = &gt->buffer_pool;
        int n;

        intel_gt_flush_buffer_pool(gt);

        for (n = 0; n < ARRAY_SIZE(pool->cache_list); n++)
                GEM_BUG_ON(!list_empty(&pool->cache_list[n]));
}