/*
 * Copyright © 2008-2015 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 */

#include <linux/oom.h>
#include <linux/sched/mm.h>
#include <linux/shmem_fs.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/pci.h>
#include <linux/dma-buf.h>
#include <linux/vmalloc.h>
#include <drm/drmP.h>
#include <drm/i915_drm.h>

#include "i915_drv.h"
#include "i915_trace.h"

static bool shrinker_lock(struct drm_i915_private *i915, bool *unlock)
{
        switch (mutex_trylock_recursive(&i915->drm.struct_mutex)) {
        case MUTEX_TRYLOCK_RECURSIVE:
                *unlock = false;
                return true;

        case MUTEX_TRYLOCK_FAILED:
                *unlock = false;
                preempt_disable();
                do {
                        cpu_relax();
                        if (mutex_trylock(&i915->drm.struct_mutex)) {
                                *unlock = true;
                                break;
                        }
                } while (!need_resched());
                preempt_enable();
                return *unlock;

        case MUTEX_TRYLOCK_SUCCESS:
                *unlock = true;
                return true;
        }

        BUG();
}

static void shrinker_unlock(struct drm_i915_private *i915, bool unlock)
{
        if (!unlock)
                return;

        mutex_unlock(&i915->drm.struct_mutex);
}

static bool swap_available(void)
{
        return get_nr_swap_pages() > 0;
}

static bool can_release_pages(struct drm_i915_gem_object *obj)
{
        /* Consider only shrinkable ojects. */
        if (!i915_gem_object_is_shrinkable(obj))
                return false;

        /* Only report true if by unbinding the object and putting its pages
         * we can actually make forward progress towards freeing physical
         * pages.
         *
         * If the pages are pinned for any other reason than being bound
         * to the GPU, simply unbinding from the GPU is not going to succeed
         * in releasing our pin count on the pages themselves.
         */
        if (atomic_read(&obj->mm.pages_pin_count) > obj->bind_count)
                return false;

        /* If any vma are "permanently" pinned, it will prevent us from
         * reclaiming the obj->mm.pages. We only allow scanout objects to claim
         * a permanent pin, along with a few others like the context objects.
         * To simplify the scan, and to avoid walking the list of vma under the
         * object, we just check the count of its permanently pinned.
         */
        if (READ_ONCE(obj->pin_global))
                return false;

        /* We can only return physical pages to the system if we can either
         * discard the contents (because the user has marked them as being
         * purgeable) or if we can move their contents out to swap.
         */
        return swap_available() || obj->mm.madv == I915_MADV_DONTNEED;
}

static bool unsafe_drop_pages(struct drm_i915_gem_object *obj)
{
        if (i915_gem_object_unbind(obj) == 0)
                __i915_gem_object_put_pages(obj, I915_MM_SHRINKER);
        return !i915_gem_object_has_pages(obj);
}

/**
 * i915_gem_shrink - Shrink buffer object caches
 * @i915: i915 device
 * @target: amount of memory to make available, in pages
 * @nr_scanned: optional output for number of pages scanned (incremental)
 * @flags: control flags for selecting cache types
 *
 * This function is the main interface to the shrinker. It will try to release
 * up to @target pages of main memory backing storage from buffer objects.
 * Selection of the specific caches can be done with @flags. This is e.g. useful
 * when purgeable objects should be removed from caches preferentially.
 *
 * Note that it's not guaranteed that released amount is actually available as
 * free system memory - the pages might still be in-used to due to other reasons
 * (like cpu mmaps) or the mm core has reused them before we could grab them.
 * Therefore code that needs to explicitly shrink buffer objects caches (e.g. to
 * avoid deadlocks in memory reclaim) must fall back to i915_gem_shrink_all().
 *
 * Also note that any kind of pinning (both per-vma address space pins and
 * backing storage pins at the buffer object level) result in the shrinker code
 * having to skip the object.
 *
 * Returns:
 * The number of pages of backing storage actually released.
 */
unsigned long
i915_gem_shrink(struct drm_i915_private *i915,
                unsigned long target,
                unsigned long *nr_scanned,
                unsigned flags)
{
        const struct {
                struct list_head *list;
                unsigned int bit;
        } phases[] = {
                { &i915->mm.unbound_list, I915_SHRINK_UNBOUND },
                { &i915->mm.bound_list, I915_SHRINK_BOUND },
                { NULL, 0 },
        }, *phase;
        unsigned long count = 0;
        unsigned long scanned = 0;
        bool unlock;

        if (!shrinker_lock(i915, &unlock))
                return 0;

        /*
         * When shrinking the active list, also consider active contexts.
         * Active contexts are pinned until they are retired, and so can
         * not be simply unbound to retire and unpin their pages. To shrink
         * the contexts, we must wait until the gpu is idle.
         *
         * We don't care about errors here; if we cannot wait upon the GPU,
         * we will free as much as we can and hope to get a second chance.
         */
        if (flags & I915_SHRINK_ACTIVE)
                i915_gem_wait_for_idle(i915,
                                       I915_WAIT_LOCKED,
                                       MAX_SCHEDULE_TIMEOUT);

        trace_i915_gem_shrink(i915, target, flags);
        i915_retire_requests(i915);

        /*
         * Unbinding of objects will require HW access; Let us not wake the
         * device just to recover a little memory. If absolutely necessary,
         * we will force the wake during oom-notifier.
         */
        if ((flags & I915_SHRINK_BOUND) &&
            !intel_runtime_pm_get_if_in_use(i915))
                flags &= ~I915_SHRINK_BOUND;

        /*
         * As we may completely rewrite the (un)bound list whilst unbinding
         * (due to retiring requests) we have to strictly process only
         * one element of the list at the time, and recheck the list
         * on every iteration.
         *
         * In particular, we must hold a reference whilst removing the
         * object as we may end up waiting for and/or retiring the objects.
         * This might release the final reference (held by the active list)
         * and result in the object being freed from under us. This is
         * similar to the precautions the eviction code must take whilst
         * removing objects.
         *
         * Also note that although these lists do not hold a reference to
         * the object we can safely grab one here: The final object
         * unreferencing and the bound_list are both protected by the
         * dev->struct_mutex and so we won't ever be able to observe an
         * object on the bound_list with a reference count equals 0.
         */
        for (phase = phases; phase->list; phase++) {
                struct list_head still_in_list;
                struct drm_i915_gem_object *obj;

                if ((flags & phase->bit) == 0)
                        continue;

                INIT_LIST_HEAD(&still_in_list);

                /*
                 * We serialize our access to unreferenced objects through
                 * the use of the struct_mutex. While the objects are not
                 * yet freed (due to RCU then a workqueue) we still want
                 * to be able to shrink their pages, so they remain on
                 * the unbound/bound list until actually freed.
                 */
                lockmgr(&i915->mm.obj_lock, LK_EXCLUSIVE);
                while (count < target &&
                       (obj = list_first_entry_or_null(phase->list,
                                                       typeof(*obj),
                                                       mm.link))) {
                        list_move_tail(&obj->mm.link, &still_in_list);

                        if (flags & I915_SHRINK_PURGEABLE &&
                            obj->mm.madv != I915_MADV_DONTNEED)
                                continue;

                        if (flags & I915_SHRINK_VMAPS &&
                            !is_vmalloc_addr(obj->mm.mapping))
                                continue;

                        if (!(flags & I915_SHRINK_ACTIVE) &&
                            (i915_gem_object_is_active(obj) ||
                             i915_gem_object_is_framebuffer(obj)))
                                continue;

                        if (!can_release_pages(obj))
                                continue;

                        lockmgr(&i915->mm.obj_lock, LK_RELEASE);

                        if (unsafe_drop_pages(obj)) {
                                /* May arrive from get_pages on another bo */
                                mutex_lock_nested(&obj->mm.lock,
                                                  I915_MM_SHRINKER);
                                if (!i915_gem_object_has_pages(obj)) {
                                        __i915_gem_object_invalidate(obj);
                                        count += obj->base.size >> PAGE_SHIFT;
                                }
                                mutex_unlock(&obj->mm.lock);
                        }
                        scanned += obj->base.size >> PAGE_SHIFT;

                        lockmgr(&i915->mm.obj_lock, LK_EXCLUSIVE);
                }
                list_splice_tail(&still_in_list, phase->list);
                lockmgr(&i915->mm.obj_lock, LK_RELEASE);
        }

        if (flags & I915_SHRINK_BOUND)
                intel_runtime_pm_put(i915);

        i915_retire_requests(i915);

        shrinker_unlock(i915, unlock);

        if (nr_scanned)
                *nr_scanned += scanned;
        return count;
}

/**
 * i915_gem_shrink_all - Shrink buffer object caches completely
 * @i915: i915 device
 *
 * This is a simple wraper around i915_gem_shrink() to aggressively shrink all
 * caches completely. It also first waits for and retires all outstanding
 * requests to also be able to release backing storage for active objects.
 *
 * This should only be used in code to intentionally quiescent the gpu or as a
 * last-ditch effort when memory seems to have run out.
 *
 * Returns:
 * The number of pages of backing storage actually released.
 */
unsigned long i915_gem_shrink_all(struct drm_i915_private *i915)
{
        unsigned long freed;

        intel_runtime_pm_get(i915);
        freed = i915_gem_shrink(i915, -1UL, NULL,
                                I915_SHRINK_BOUND |
                                I915_SHRINK_UNBOUND |
                                I915_SHRINK_ACTIVE);
        intel_runtime_pm_put(i915);

        return freed;
}

static unsigned long
i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
{
#if 0
        struct drm_i915_private *i915 =
                container_of(shrinker, struct drm_i915_private, mm.shrinker);
        struct drm_i915_gem_object *obj;
        unsigned long num_objects = 0;
        unsigned long count = 0;

        spin_lock(&i915->mm.obj_lock);
        list_for_each_entry(obj, &i915->mm.unbound_list, mm.link)
                if (can_release_pages(obj)) {
                        count += obj->base.size >> PAGE_SHIFT;
                        num_objects++;
                }

        list_for_each_entry(obj, &i915->mm.bound_list, mm.link)
                if (!i915_gem_object_is_active(obj) && can_release_pages(obj)) {
                        count += obj->base.size >> PAGE_SHIFT;
                        num_objects++;
                }
        spin_unlock(&i915->mm.obj_lock);

        /* Update our preferred vmscan batch size for the next pass.
         * Our rough guess for an effective batch size is roughly 2
         * available GEM objects worth of pages. That is we don't want
         * the shrinker to fire, until it is worth the cost of freeing an
         * entire GEM object.
         */
        if (num_objects) {
                unsigned long avg = 2 * count / num_objects;

                i915->mm.shrinker.batch =
                        max((i915->mm.shrinker.batch + avg) >> 1,
                            128ul /* default SHRINK_BATCH */);
        }

        return count;
#endif
        return 0;
}

static unsigned long
i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
{
#if 0
        struct drm_i915_private *i915 =
                container_of(shrinker, struct drm_i915_private, mm.shrinker);
        unsigned long freed;
        bool unlock;

        sc->nr_scanned = 0;

        if (!shrinker_lock(i915, &unlock))
                return SHRINK_STOP;

        freed = i915_gem_shrink(i915,
                                sc->nr_to_scan,
                                &sc->nr_scanned,
                                I915_SHRINK_BOUND |
                                I915_SHRINK_UNBOUND |
                                I915_SHRINK_PURGEABLE);
        if (sc->nr_scanned < sc->nr_to_scan)
                freed += i915_gem_shrink(i915,
                                         sc->nr_to_scan - sc->nr_scanned,
                                         &sc->nr_scanned,
                                         I915_SHRINK_BOUND |
                                         I915_SHRINK_UNBOUND);
        if (sc->nr_scanned < sc->nr_to_scan && current_is_kswapd()) {
                intel_runtime_pm_get(i915);
                freed += i915_gem_shrink(i915,
                                         sc->nr_to_scan - sc->nr_scanned,
                                         &sc->nr_scanned,
                                         I915_SHRINK_ACTIVE |
                                         I915_SHRINK_BOUND |
                                         I915_SHRINK_UNBOUND);
                intel_runtime_pm_put(i915);
        }

        shrinker_unlock(i915, unlock);

        return sc->nr_scanned ? freed : SHRINK_STOP;
#endif
        return 0;
}

#if 0
static bool
shrinker_lock_uninterruptible(struct drm_i915_private *i915, bool *unlock,
                              int timeout_ms)
{
        unsigned long timeout = jiffies + msecs_to_jiffies_timeout(timeout_ms);

        do {
                if (i915_gem_wait_for_idle(i915,
                                           0, MAX_SCHEDULE_TIMEOUT) == 0 &&
                    shrinker_lock(i915, unlock))
                        break;

                schedule_timeout_killable(1);
                if (fatal_signal_pending(current))
                        return false;

                if (time_after(jiffies, timeout)) {
                        pr_err("Unable to lock GPU to purge memory.\n");
                        return false;
                }
        } while (1);

        return true;
}

static int
i915_gem_shrinker_oom(struct notifier_block *nb, unsigned long event, void *ptr)
{
        struct drm_i915_private *i915 =
                container_of(nb, struct drm_i915_private, mm.oom_notifier);
        struct drm_i915_gem_object *obj;
        unsigned long unevictable, bound, unbound, freed_pages;

        freed_pages = i915_gem_shrink_all(i915);

        /* Because we may be allocating inside our own driver, we cannot
         * assert that there are no objects with pinned pages that are not
         * being pointed to by hardware.
         */
        unbound = bound = unevictable = 0;
        spin_lock(&i915->mm.obj_lock);
        list_for_each_entry(obj, &i915->mm.unbound_list, mm.link) {
                if (!can_release_pages(obj))
                        unevictable += obj->base.size >> PAGE_SHIFT;
                else
                        unbound += obj->base.size >> PAGE_SHIFT;
        }
        list_for_each_entry(obj, &i915->mm.bound_list, mm.link) {
                if (!can_release_pages(obj))
                        unevictable += obj->base.size >> PAGE_SHIFT;
                else
                        bound += obj->base.size >> PAGE_SHIFT;
        }
        spin_unlock(&i915->mm.obj_lock);

        if (freed_pages || unbound || bound)
                pr_info("Purging GPU memory, %lu pages freed, "
                        "%lu pages still pinned.\n",
                        freed_pages, unevictable);
        if (unbound || bound)
                pr_err("%lu and %lu pages still available in the "
                       "bound and unbound GPU page lists.\n",
                       bound, unbound);

        *(unsigned long *)ptr += freed_pages;
        return NOTIFY_DONE;
}

static int
i915_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
{
        struct drm_i915_private *i915 =
                container_of(nb, struct drm_i915_private, mm.vmap_notifier);
        struct i915_vma *vma, *next;
        unsigned long freed_pages = 0;
        bool unlock;
        int ret;

        if (!shrinker_lock_uninterruptible(i915, &unlock, 5000))
                return NOTIFY_DONE;

        /* Force everything onto the inactive lists */
        ret = i915_gem_wait_for_idle(i915,
                                     I915_WAIT_LOCKED,
                                     MAX_SCHEDULE_TIMEOUT);
        if (ret)
                goto out;

        intel_runtime_pm_get(i915);
        freed_pages += i915_gem_shrink(i915, -1UL, NULL,
                                       I915_SHRINK_BOUND |
                                       I915_SHRINK_UNBOUND |
                                       I915_SHRINK_ACTIVE |
                                       I915_SHRINK_VMAPS);
        intel_runtime_pm_put(i915);

        /* We also want to clear any cached iomaps as they wrap vmap */
        list_for_each_entry_safe(vma, next,
                                 &i915->ggtt.vm.inactive_list, vm_link) {
                unsigned long count = vma->node.size >> PAGE_SHIFT;
                if (vma->iomap && i915_vma_unbind(vma) == 0)
                        freed_pages += count;
        }

out:
        shrinker_unlock(i915, unlock);

        *(unsigned long *)ptr += freed_pages;
        return NOTIFY_DONE;
}
#endif

/**
 * i915_gem_shrinker_register - Register the i915 shrinker
 * @i915: i915 device
 *
 * This function registers and sets up the i915 shrinker and OOM handler.
 */
void i915_gem_shrinker_register(struct drm_i915_private *i915)
{
        i915->mm.shrinker.scan_objects = i915_gem_shrinker_scan;
        i915->mm.shrinker.count_objects = i915_gem_shrinker_count;
        i915->mm.shrinker.seeks = DEFAULT_SEEKS;
#if 0
        i915->mm.shrinker.batch = 4096;
#endif
#if 0
        WARN_ON(register_shrinker(&i915->mm.shrinker));

        i915->mm.oom_notifier.notifier_call = i915_gem_shrinker_oom;
        WARN_ON(register_oom_notifier(&i915->mm.oom_notifier));

        i915->mm.vmap_notifier.notifier_call = i915_gem_shrinker_vmap;
        WARN_ON(register_vmap_purge_notifier(&i915->mm.vmap_notifier));
#endif
}

/**
 * i915_gem_shrinker_unregister - Unregisters the i915 shrinker
 * @i915: i915 device
 *
 * This function unregisters the i915 shrinker and OOM handler.
 */
void i915_gem_shrinker_unregister(struct drm_i915_private *i915)
{
#if 0
        WARN_ON(unregister_vmap_purge_notifier(&i915->mm.vmap_notifier));
        WARN_ON(unregister_oom_notifier(&i915->mm.oom_notifier));
        unregister_shrinker(&i915->mm.shrinker);
#endif
}

void i915_gem_shrinker_taints_mutex(struct lock *mutex)
{
        if (!IS_ENABLED(CONFIG_LOCKDEP))
                return;

        fs_reclaim_acquire(GFP_KERNEL);
        mutex_lock(mutex);
        mutex_unlock(mutex);
        fs_reclaim_release(GFP_KERNEL);
}