// SPDX-License-Identifier: MIT
/*
 * Copyright © 2008-2015 Intel Corporation
 */

#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 "gt/intel_gt_requests.h"
#include "gt/intel_gt.h"

#include "i915_trace.h"

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 objects. */
        if (!i915_gem_object_is_shrinkable(obj))
                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 drop_pages(struct drm_i915_gem_object *obj,
                       unsigned long shrink, bool trylock_vm)
{
        unsigned long flags;

        flags = 0;
        if (shrink & I915_SHRINK_ACTIVE)
                flags |= I915_GEM_OBJECT_UNBIND_ACTIVE;
        if (!(shrink & I915_SHRINK_BOUND))
                flags |= I915_GEM_OBJECT_UNBIND_TEST;
        if (trylock_vm)
                flags |= I915_GEM_OBJECT_UNBIND_VM_TRYLOCK;

        if (i915_gem_object_unbind(obj, flags) == 0)
                return true;

        return false;
}

static int try_to_writeback(struct drm_i915_gem_object *obj, unsigned int flags)
{
        if (obj->ops->shrink) {
                unsigned int shrink_flags = 0;

                if (!(flags & I915_SHRINK_ACTIVE))
                        shrink_flags |= I915_GEM_OBJECT_SHRINK_NO_GPU_WAIT;

                if (flags & I915_SHRINK_WRITEBACK)
                        shrink_flags |= I915_GEM_OBJECT_SHRINK_WRITEBACK;

                return obj->ops->shrink(obj, shrink_flags);
        }

        return 0;
}

/**
 * i915_gem_shrink - Shrink buffer object caches
 * @ww: i915 gem ww acquire ctx, or NULL
 * @i915: i915 device
 * @target: amount of memory to make available, in pages
 * @nr_scanned: optional output for number of pages scanned (incremental)
 * @shrink: 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 i915_gem_ww_ctx *ww,
                struct drm_i915_private *i915,
                unsigned long target,
                unsigned long *nr_scanned,
                unsigned int shrink)
{
        const struct {
                struct list_head *list;
                unsigned int bit;
        } phases[] = {
                { &i915->mm.purge_list, ~0u },
                {
                        &i915->mm.shrink_list,
                        I915_SHRINK_BOUND | I915_SHRINK_UNBOUND
                },
                { NULL, 0 },
        }, *phase;
        intel_wakeref_t wakeref = NULL;
        unsigned long count = 0;
        unsigned long scanned = 0;
        int err = 0, i = 0;
        struct intel_gt *gt;

        /* CHV + VTD workaround use stop_machine(); need to trylock vm->mutex */
        bool trylock_vm = !ww && intel_vm_no_concurrent_access_wa(i915);

        trace_i915_gem_shrink(i915, target, shrink);

        /*
         * 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 (shrink & I915_SHRINK_BOUND) {
                wakeref = intel_runtime_pm_get_if_in_use(&i915->runtime_pm);
                if (!wakeref)
                        shrink &= ~I915_SHRINK_BOUND;
        }

        /*
         * When shrinking the active list, we should 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 and
         * completed its switch to the kernel context. In short, we do
         * not have a good mechanism for idling a specific context, but
         * what we can do is give them a kick so that we do not keep idle
         * contexts around longer than is necessary.
         */
        if (shrink & I915_SHRINK_ACTIVE) {
                for_each_gt(gt, i915, i)
                        /* Retire requests to unpin all idle contexts */
                        intel_gt_retire_requests(gt);
        }

        /*
         * 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
         * i915->mm.obj_lock 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;
                unsigned long flags;

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

                INIT_LIST_HEAD(&still_in_list);

                /*
                 * We serialize our access to unreferenced objects through
                 * the use of the obj_lock. 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.
                 */
                spin_lock_irqsave(&i915->mm.obj_lock, flags);
                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 (shrink & I915_SHRINK_VMAPS &&
                            !is_vmalloc_addr(obj->mm.mapping))
                                continue;

                        if (!(shrink & I915_SHRINK_ACTIVE) &&
                            i915_gem_object_is_framebuffer(obj))
                                continue;

                        if (!can_release_pages(obj))
                                continue;

                        if (!kref_get_unless_zero(&obj->base.refcount))
                                continue;

                        spin_unlock_irqrestore(&i915->mm.obj_lock, flags);

                        /* May arrive from get_pages on another bo */
                        if (!ww) {
                                if (!i915_gem_object_trylock(obj, NULL))
                                        goto skip;
                        } else {
                                err = i915_gem_object_lock(obj, ww);
                                if (err)
                                        goto skip;
                        }

                        if (drop_pages(obj, shrink, trylock_vm) &&
                            !__i915_gem_object_put_pages(obj) &&
                            !try_to_writeback(obj, shrink))
                                count += obj->base.size >> PAGE_SHIFT;

                        if (!ww)
                                i915_gem_object_unlock(obj);

                        scanned += obj->base.size >> PAGE_SHIFT;
skip:
                        i915_gem_object_put(obj);

                        spin_lock_irqsave(&i915->mm.obj_lock, flags);
                        if (err)
                                break;
                }
                list_splice_tail(&still_in_list, phase->list);
                spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
                if (err)
                        break;
        }

        if (shrink & I915_SHRINK_BOUND)
                intel_runtime_pm_put(&i915->runtime_pm, wakeref);

        if (err)
                return err;

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

/**
 * i915_gem_shrink_all - Shrink buffer object caches completely
 * @i915: i915 device
 *
 * This is a simple wrapper 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)
{
        intel_wakeref_t wakeref;
        unsigned long freed = 0;

        with_intel_runtime_pm(&i915->runtime_pm, wakeref) {
                freed = i915_gem_shrink(NULL, i915, -1UL, NULL,
                                        I915_SHRINK_BOUND |
                                        I915_SHRINK_UNBOUND);
        }

        return freed;
}

static unsigned long
i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
{
        struct drm_i915_private *i915 = shrinker->private_data;
        unsigned long num_objects;
        unsigned long count;

        count = READ_ONCE(i915->mm.shrink_memory) >> PAGE_SHIFT;
        num_objects = READ_ONCE(i915->mm.shrink_count);

        /*
         * 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;
}

static unsigned long
i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
{
        struct drm_i915_private *i915 = shrinker->private_data;
        unsigned long freed;

        sc->nr_scanned = 0;

        freed = i915_gem_shrink(NULL, i915,
                                sc->nr_to_scan,
                                &sc->nr_scanned,
                                I915_SHRINK_BOUND |
                                I915_SHRINK_UNBOUND);
        if (sc->nr_scanned < sc->nr_to_scan && current_is_kswapd()) {
                intel_wakeref_t wakeref;

                with_intel_runtime_pm(&i915->runtime_pm, wakeref) {
                        freed += i915_gem_shrink(NULL, i915,
                                                 sc->nr_to_scan - sc->nr_scanned,
                                                 &sc->nr_scanned,
                                                 I915_SHRINK_ACTIVE |
                                                 I915_SHRINK_BOUND |
                                                 I915_SHRINK_UNBOUND |
                                                 I915_SHRINK_WRITEBACK);
                }
        }

        return sc->nr_scanned ? freed : SHRINK_STOP;
}

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, available, freed_pages;
        intel_wakeref_t wakeref;
        unsigned long flags;

        freed_pages = 0;
        with_intel_runtime_pm(&i915->runtime_pm, wakeref)
                freed_pages += i915_gem_shrink(NULL, i915, -1UL, NULL,
                                               I915_SHRINK_BOUND |
                                               I915_SHRINK_UNBOUND |
                                               I915_SHRINK_WRITEBACK);

        /* 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.
         */
        available = unevictable = 0;
        spin_lock_irqsave(&i915->mm.obj_lock, flags);
        list_for_each_entry(obj, &i915->mm.shrink_list, mm.link) {
                if (!can_release_pages(obj))
                        unevictable += obj->base.size >> PAGE_SHIFT;
                else
                        available += obj->base.size >> PAGE_SHIFT;
        }
        spin_unlock_irqrestore(&i915->mm.obj_lock, flags);

        if (freed_pages || available)
                pr_info("Purging GPU memory, %lu pages freed, "
                        "%lu pages still pinned, %lu pages left available.\n",
                        freed_pages, unevictable, available);

        *(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;
        intel_wakeref_t wakeref;
        struct intel_gt *gt;
        int i;

        with_intel_runtime_pm(&i915->runtime_pm, wakeref)
                freed_pages += i915_gem_shrink(NULL, i915, -1UL, NULL,
                                               I915_SHRINK_BOUND |
                                               I915_SHRINK_UNBOUND |
                                               I915_SHRINK_VMAPS);

        /* We also want to clear any cached iomaps as they wrap vmap */
        for_each_gt(gt, i915, i) {
                mutex_lock(&gt->ggtt->vm.mutex);
                list_for_each_entry_safe(vma, next,
                                         &gt->ggtt->vm.bound_list, vm_link) {
                        unsigned long count = i915_vma_size(vma) >> PAGE_SHIFT;
                        struct drm_i915_gem_object *obj = vma->obj;

                        if (!vma->iomap || i915_vma_is_active(vma))
                                continue;

                        if (!i915_gem_object_trylock(obj, NULL))
                                continue;

                        if (__i915_vma_unbind(vma) == 0)
                                freed_pages += count;

                        i915_gem_object_unlock(obj);
                }
                mutex_unlock(&gt->ggtt->vm.mutex);
        }

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

void i915_gem_driver_register__shrinker(struct drm_i915_private *i915)
{
        i915->mm.shrinker = shrinker_alloc(0, "drm-i915_gem");
        if (!i915->mm.shrinker) {
                drm_WARN_ON(&i915->drm, 1);
        } else {
                i915->mm.shrinker->scan_objects = i915_gem_shrinker_scan;
                i915->mm.shrinker->count_objects = i915_gem_shrinker_count;
                i915->mm.shrinker->batch = 4096;
                i915->mm.shrinker->private_data = i915;

                shrinker_register(i915->mm.shrinker);
        }

#ifdef notyet
        i915->mm.oom_notifier.notifier_call = i915_gem_shrinker_oom;
        drm_WARN_ON(&i915->drm, register_oom_notifier(&i915->mm.oom_notifier));

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

void i915_gem_driver_unregister__shrinker(struct drm_i915_private *i915)
{
#ifdef notyet
        drm_WARN_ON(&i915->drm,
                    unregister_vmap_purge_notifier(&i915->mm.vmap_notifier));
        drm_WARN_ON(&i915->drm,
                    unregister_oom_notifier(&i915->mm.oom_notifier));
#endif
        shrinker_free(i915->mm.shrinker);
}

void i915_gem_shrinker_taints_mutex(struct drm_i915_private *i915,
                                    struct rwlock *mutex)
{
#ifdef notyet
        if (!IS_ENABLED(CONFIG_LOCKDEP))
                return;

        fs_reclaim_acquire(GFP_KERNEL);

        mutex_acquire(&mutex->dep_map, 0, 0, _RET_IP_);
        mutex_release(&mutex->dep_map, _RET_IP_);

        fs_reclaim_release(GFP_KERNEL);
#endif
}

/**
 * i915_gem_object_make_unshrinkable - Hide the object from the shrinker. By
 * default all object types that support shrinking(see IS_SHRINKABLE), will also
 * make the object visible to the shrinker after allocating the system memory
 * pages.
 * @obj: The GEM object.
 *
 * This is typically used for special kernel internal objects that can't be
 * easily processed by the shrinker, like if they are perma-pinned.
 */
void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj)
{
        struct drm_i915_private *i915 = obj_to_i915(obj);
        unsigned long flags;

        /*
         * We can only be called while the pages are pinned or when
         * the pages are released. If pinned, we should only be called
         * from a single caller under controlled conditions; and on release
         * only one caller may release us. Neither the two may cross.
         */
        if (atomic_add_unless(&obj->mm.shrink_pin, 1, 0))
                return;

        spin_lock_irqsave(&i915->mm.obj_lock, flags);
        if (!atomic_fetch_inc(&obj->mm.shrink_pin) &&
            !list_empty(&obj->mm.link)) {
                list_del_init(&obj->mm.link);
                i915->mm.shrink_count--;
                i915->mm.shrink_memory -= obj->base.size;
        }
        spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
}

static void ___i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj,
                                               struct list_head *head)
{
        struct drm_i915_private *i915 = obj_to_i915(obj);
        unsigned long flags;

        if (!i915_gem_object_is_shrinkable(obj))
                return;

        if (atomic_add_unless(&obj->mm.shrink_pin, -1, 1))
                return;

        spin_lock_irqsave(&i915->mm.obj_lock, flags);
        GEM_BUG_ON(!kref_read(&obj->base.refcount));
        if (atomic_dec_and_test(&obj->mm.shrink_pin)) {
                GEM_BUG_ON(!list_empty(&obj->mm.link));

                list_add_tail(&obj->mm.link, head);
                i915->mm.shrink_count++;
                i915->mm.shrink_memory += obj->base.size;

        }
        spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
}

/**
 * __i915_gem_object_make_shrinkable - Move the object to the tail of the
 * shrinkable list. Objects on this list might be swapped out. Used with
 * WILLNEED objects.
 * @obj: The GEM object.
 *
 * DO NOT USE. This is intended to be called on very special objects that don't
 * yet have mm.pages, but are guaranteed to have potentially reclaimable pages
 * underneath.
 */
void __i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj)
{
        ___i915_gem_object_make_shrinkable(obj,
                                           &obj_to_i915(obj)->mm.shrink_list);
}

/**
 * __i915_gem_object_make_purgeable - Move the object to the tail of the
 * purgeable list. Objects on this list might be swapped out. Used with
 * DONTNEED objects.
 * @obj: The GEM object.
 *
 * DO NOT USE. This is intended to be called on very special objects that don't
 * yet have mm.pages, but are guaranteed to have potentially reclaimable pages
 * underneath.
 */
void __i915_gem_object_make_purgeable(struct drm_i915_gem_object *obj)
{
        ___i915_gem_object_make_shrinkable(obj,
                                           &obj_to_i915(obj)->mm.purge_list);
}

/**
 * i915_gem_object_make_shrinkable - Move the object to the tail of the
 * shrinkable list. Objects on this list might be swapped out. Used with
 * WILLNEED objects.
 * @obj: The GEM object.
 *
 * MUST only be called on objects which have backing pages.
 *
 * MUST be balanced with previous call to i915_gem_object_make_unshrinkable().
 */
void i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj)
{
        GEM_BUG_ON(!i915_gem_object_has_pages(obj));
        __i915_gem_object_make_shrinkable(obj);
}

/**
 * i915_gem_object_make_purgeable - Move the object to the tail of the purgeable
 * list. Used with DONTNEED objects. Unlike with shrinkable objects, the
 * shrinker will attempt to discard the backing pages, instead of trying to swap
 * them out.
 * @obj: The GEM object.
 *
 * MUST only be called on objects which have backing pages.
 *
 * MUST be balanced with previous call to i915_gem_object_make_unshrinkable().
 */
void i915_gem_object_make_purgeable(struct drm_i915_gem_object *obj)
{
        GEM_BUG_ON(!i915_gem_object_has_pages(obj));
        __i915_gem_object_make_purgeable(obj);
}