Re: [PATCH v6 17/22] drm/shmem-helper: Add generic memory shrinker

Rob Clark
2022-06-19T17:53:03Z

On Thu, May 26, 2022 at 4:55 PM Dmitry Osipenko
<dmitry.osipenko@collabora.com> wrote:
>
> Introduce a common DRM SHMEM shrinker framework that allows to reduce
> code duplication among DRM drivers by replacing theirs custom shrinker
> implementations with the generic shrinker.
>
> In order to start using DRM SHMEM shrinker drivers should:
>
> 1. Implement new evict() shmem object callback.
> 2. Register shrinker using drm_gem_shmem_shrinker_register(drm_device).
> 3. Use drm_gem_shmem_set_purgeable(shmem) and alike API functions to
> activate shrinking of shmem GEMs.
>
> This patch is based on a ideas borrowed from Rob's Clark MSM shrinker,
> Thomas' Zimmermann variant of SHMEM shrinker and Intel's i915 shrinker.
>
> Signed-off-by: Daniel Almeida <daniel.almeida@collabora.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 540 ++++++++++++++++--
> .../gpu/drm/panfrost/panfrost_gem_shrinker.c | 9 +-
> drivers/gpu/drm/virtio/virtgpu_drv.h | 3 +
> include/drm/drm_device.h | 4 +
> include/drm/drm_gem_shmem_helper.h | 87 ++-
> 5 files changed, 594 insertions(+), 49 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 555fe212bd98..4cd0b5913492 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -126,6 +126,42 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_create);
>
> +static bool drm_gem_shmem_is_evictable(struct drm_gem_shmem_object *shmem)
> +{
> + return (shmem->madv >= 0) && shmem->evict &&
> + shmem->eviction_enabled && shmem->pages_use_count &&
> + !shmem->pages_pin_count && !shmem->base.dma_buf &&
> + !shmem->base.import_attach && shmem->sgt && !shmem->evicted;
> +}
> +
> +static void
> +drm_gem_shmem_update_pages_state(struct drm_gem_shmem_object *shmem)
> +{
> + struct drm_gem_object *obj = &shmem->base;
> + struct drm_gem_shmem_shrinker *gem_shrinker = obj->dev->shmem_shrinker;
> +
> + dma_resv_assert_held(shmem->base.resv);
> +
> + if (!gem_shrinker || obj->import_attach)
> + return;
> +
> + mutex_lock(&gem_shrinker->lock);
> +
> + if (drm_gem_shmem_is_evictable(shmem) ||
> + drm_gem_shmem_is_purgeable(shmem))
> + list_move_tail(&shmem->madv_list, &gem_shrinker->lru_evictable);
> + else if (shmem->madv < 0)
> + list_del_init(&shmem->madv_list);
> + else if (shmem->evicted)
> + list_move_tail(&shmem->madv_list, &gem_shrinker->lru_evicted);
> + else if (!shmem->pages)
> + list_del_init(&shmem->madv_list);
> + else
> + list_move_tail(&shmem->madv_list, &gem_shrinker->lru_pinned);
> +
> + mutex_unlock(&gem_shrinker->lock);
> +}
> +
> /**
> * drm_gem_shmem_free - Free resources associated with a shmem GEM object
> * @shmem: shmem GEM object to free
> @@ -142,6 +178,9 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> } else {
> dma_resv_lock(shmem->base.resv, NULL);
>
> + /* take out shmem GEM object from the memory shrinker */
> + drm_gem_shmem_madvise(shmem, -1);
> +
> WARN_ON(shmem->vmap_use_count);
>
> if (shmem->sgt) {
> @@ -150,7 +189,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> sg_free_table(shmem->sgt);
> kfree(shmem->sgt);
> }
> - if (shmem->pages)
> + if (shmem->pages_use_count)
> drm_gem_shmem_put_pages(shmem);
>
> WARN_ON(shmem->pages_use_count);
> @@ -163,18 +202,82 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_free);
>
> -static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> +/**
> + * drm_gem_shmem_set_evictable() - Make GEM evictable by memory shrinker
> + * @shmem: shmem GEM object
> + *
> + * Tell memory shrinker that this GEM can be evicted. Initially eviction is
> + * disabled for all GEMs. If GEM was purged, then -ENOMEM is returned.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_shmem_set_evictable(struct drm_gem_shmem_object *shmem)
> +{
> + dma_resv_lock(shmem->base.resv, NULL);
> +
> + if (shmem->madv < 0)
> + return -ENOMEM;
> +
> + shmem->eviction_enabled = true;
> +
> + dma_resv_unlock(shmem->base.resv);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_set_evictable);
> +
> +/**
> + * drm_gem_shmem_set_purgeable() - Make GEM purgeable by memory shrinker
> + * @shmem: shmem GEM object
> + *
> + * Tell memory shrinker that this GEM can be purged. Initially purging is
> + * disabled for all GEMs. If GEM was purged, then -ENOMEM is returned.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_shmem_set_purgeable(struct drm_gem_shmem_object *shmem)
> +{
> + dma_resv_lock(shmem->base.resv, NULL);
> +
> + if (shmem->madv < 0)
> + return -ENOMEM;
> +
> + shmem->purge_enabled = true;
> +
> + drm_gem_shmem_update_pages_state(shmem);
> +
> + dma_resv_unlock(shmem->base.resv);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_set_purgeable);
> +
> +static int
> +drm_gem_shmem_acquire_pages(struct drm_gem_shmem_object *shmem)
> {
> struct drm_gem_object *obj = &shmem->base;
> struct page **pages;
>
> - if (shmem->pages_use_count++ > 0)
> + dma_resv_assert_held(shmem->base.resv);
> +
> + if (shmem->madv < 0) {
> + WARN_ON(shmem->pages);
> + return -ENOMEM;
> + }
> +
> + if (shmem->pages) {
> + WARN_ON(!shmem->evicted);
> return 0;
> + }
> +
> + if (WARN_ON(!shmem->pages_use_count))
> + return -EINVAL;
>
> pages = drm_gem_get_pages(obj);
> if (IS_ERR(pages)) {
> DRM_DEBUG_KMS("Failed to get pages (%ld)\n", PTR_ERR(pages));
> - shmem->pages_use_count = 0;
> return PTR_ERR(pages);
> }
>
> @@ -193,6 +296,58 @@ static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> return 0;
> }
>
> +static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> +{
> + int err;
> +
> + dma_resv_assert_held(shmem->base.resv);
> +
> + if (shmem->madv < 0)
> + return -ENOMEM;
> +
> + if (shmem->pages_use_count++ > 0) {
> + err = drm_gem_shmem_swap_in(shmem);
> + if (err)
> + goto err_zero_use;
> +
> + return 0;
> + }
> +
> + err = drm_gem_shmem_acquire_pages(shmem);
> + if (err)
> + goto err_zero_use;
> +
> + drm_gem_shmem_update_pages_state(shmem);
> +
> + return 0;
> +
> +err_zero_use:
> + shmem->pages_use_count = 0;
> +
> + return err;
> +}
> +
> +static void
> +drm_gem_shmem_release_pages(struct drm_gem_shmem_object *shmem)
> +{
> + struct drm_gem_object *obj = &shmem->base;
> +
> + if (!shmem->pages) {
> + WARN_ON(!shmem->evicted && shmem->madv >= 0);
> + return;
> + }
> +
> +#ifdef CONFIG_X86
> + if (shmem->map_wc)
> + set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
> +#endif
> +
> + drm_gem_put_pages(obj, shmem->pages,
> + shmem->pages_mark_dirty_on_put,
> + shmem->pages_mark_accessed_on_put);
> + shmem->pages = NULL;
> +}
> +
> /*
> * drm_gem_shmem_put_pages - Decrease use count on the backing pages for a shmem GEM object
> * @shmem: shmem GEM object
> @@ -201,8 +356,6 @@ static int drm_gem_shmem_get_pages(struct drm_gem_shmem_object *shmem)
> */
> void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
> {
> - struct drm_gem_object *obj = &shmem->base;
> -
> dma_resv_assert_held(shmem->base.resv);
>
> if (WARN_ON_ONCE(!shmem->pages_use_count))
> @@ -211,15 +364,9 @@ void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
> if (--shmem->pages_use_count > 0)
> return;
>
> -#ifdef CONFIG_X86
> - if (shmem->map_wc)
> - set_pages_array_wb(shmem->pages, obj->size >> PAGE_SHIFT);
> -#endif
> + drm_gem_shmem_release_pages(shmem);
>
> - drm_gem_put_pages(obj, shmem->pages,
> - shmem->pages_mark_dirty_on_put,
> - shmem->pages_mark_accessed_on_put);
> - shmem->pages = NULL;
> + drm_gem_shmem_update_pages_state(shmem);
> }
> EXPORT_SYMBOL(drm_gem_shmem_put_pages);
>
> @@ -235,11 +382,17 @@ EXPORT_SYMBOL(drm_gem_shmem_put_pages);
> */
> int drm_gem_shmem_pin(struct drm_gem_shmem_object *shmem)
> {
> + int ret;
> +
> dma_resv_assert_held(shmem->base.resv);
>
> WARN_ON(shmem->base.import_attach);
>
> - return drm_gem_shmem_get_pages(shmem);
> + ret = drm_gem_shmem_get_pages(shmem);
> + if (!ret)
> + shmem->pages_pin_count++;
> +
> + return ret;
> }
> EXPORT_SYMBOL(drm_gem_shmem_pin);
>
> @@ -257,6 +410,8 @@ void drm_gem_shmem_unpin(struct drm_gem_shmem_object *shmem)
> WARN_ON(shmem->base.import_attach);
>
> drm_gem_shmem_put_pages(shmem);
> +
> + shmem->pages_pin_count--;
> }
> EXPORT_SYMBOL(drm_gem_shmem_unpin);
>
> @@ -299,7 +454,7 @@ int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
> return 0;
> }
>
> - ret = drm_gem_shmem_get_pages(shmem);
> + ret = drm_gem_shmem_pin(shmem);
> if (ret)
> goto err_zero_use;
>
> @@ -322,7 +477,7 @@ int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
>
> err_put_pages:
> if (!obj->import_attach)
> - drm_gem_shmem_put_pages(shmem);
> + drm_gem_shmem_unpin(shmem);
> err_zero_use:
> shmem->vmap_use_count = 0;
>
> @@ -359,7 +514,7 @@ void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem,
> return;
>
> vunmap(shmem->vaddr);
> - drm_gem_shmem_put_pages(shmem);
> + drm_gem_shmem_unpin(shmem);
> }
>
> shmem->vaddr = NULL;
> @@ -403,41 +558,77 @@ int drm_gem_shmem_madvise(struct drm_gem_shmem_object *shmem, int madv)
>
> madv = shmem->madv;
>
> + drm_gem_shmem_update_pages_state(shmem);
> +
> return (madv >= 0);
> }
> EXPORT_SYMBOL(drm_gem_shmem_madvise);
>
> -void drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem)
> +/**
> + * drm_gem_shmem_swap_in() - Moves shmem GEM back to memory and enables
> + * hardware access to the memory.
> + * @shmem: shmem GEM object
> + *
> + * This function moves shmem GEM back to memory if it was previously evicted
> + * by the memory shrinker. The GEM is ready to use on success.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_shmem_swap_in(struct drm_gem_shmem_object *shmem)
> {
> struct drm_gem_object *obj = &shmem->base;
> - struct drm_device *dev = obj->dev;
> + struct sg_table *sgt;
> + int err;
>
> dma_resv_assert_held(shmem->base.resv);
>
> - WARN_ON(!drm_gem_shmem_is_purgeable(shmem));
> + if (shmem->evicted) {
> + err = drm_gem_shmem_acquire_pages(shmem);
> + if (err)
> + return err;
> +
> + sgt = drm_gem_shmem_get_sg_table(shmem);
> + if (IS_ERR(sgt))
> + return PTR_ERR(sgt);
> +
> + err = dma_map_sgtable(obj->dev->dev, sgt,
> + DMA_BIDIRECTIONAL, 0);
> + if (err) {
> + sg_free_table(sgt);
> + kfree(sgt);
> + return err;
> + }
>
> - dma_unmap_sgtable(dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
> - sg_free_table(shmem->sgt);
> - kfree(shmem->sgt);
> - shmem->sgt = NULL;
> + shmem->sgt = sgt;
> + shmem->evicted = false;
>
> - drm_gem_shmem_put_pages(shmem);
> + drm_gem_shmem_update_pages_state(shmem);
> + }
>
> - shmem->madv = -1;
> + if (!shmem->pages)
> + return -ENOMEM;
>
> - drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
> - drm_gem_free_mmap_offset(obj);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_swap_in);
>
> - /* Our goal here is to return as much of the memory as
> - * is possible back to the system as we are called from OOM.
> - * To do this we must instruct the shmfs to drop all of its
> - * backing pages, *now*.
> - */
> - shmem_truncate_range(file_inode(obj->filp), 0, (loff_t)-1);
> +static void drm_gem_shmem_unpin_pages(struct drm_gem_shmem_object *shmem)
> +{
> + struct drm_gem_object *obj = &shmem->base;
> + struct drm_device *dev = obj->dev;
>
> - invalidate_mapping_pages(file_inode(obj->filp)->i_mapping, 0, (loff_t)-1);
> + if (shmem->evicted)
> + return;
> +
> + dma_unmap_sgtable(dev->dev, shmem->sgt, DMA_BIDIRECTIONAL, 0);
> + drm_gem_shmem_release_pages(shmem);
> + drm_vma_node_unmap(&obj->vma_node, dev->anon_inode->i_mapping);
> +
> + sg_free_table(shmem->sgt);
> + kfree(shmem->sgt);
> + shmem->sgt = NULL;
> }
> -EXPORT_SYMBOL(drm_gem_shmem_purge);
>
> /**
> * drm_gem_shmem_dumb_create - Create a dumb shmem buffer object
> @@ -488,22 +679,33 @@ static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
> vm_fault_t ret;
> struct page *page;
> pgoff_t page_offset;
> + bool pages_unpinned;
> + int err;
>
> /* We don't use vmf->pgoff since that has the fake offset */
> page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
>
> dma_resv_lock(shmem->base.resv, NULL);
>
> - if (page_offset >= num_pages ||
> - WARN_ON_ONCE(!shmem->pages) ||
> - shmem->madv < 0) {
> + /* Sanity-check that we have the pages pointer when it should present */
> + pages_unpinned = (shmem->evicted || shmem->madv < 0 || !shmem->pages_use_count);
> + WARN_ON_ONCE(!shmem->pages ^ pages_unpinned);
> +
> + if (page_offset >= num_pages || (!shmem->pages && !shmem->evicted)) {
> ret = VM_FAULT_SIGBUS;
> } else {
> + err = drm_gem_shmem_swap_in(shmem);
> + if (err) {
> + ret = VM_FAULT_OOM;
> + goto unlock;
> + }
> +
> page = shmem->pages[page_offset];
>
> ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
> }
>
> +unlock:
> dma_resv_unlock(shmem->base.resv);
>
> return ret;
> @@ -513,13 +715,15 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)
> {
> struct drm_gem_object *obj = vma->vm_private_data;
> struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
> - int ret;
>
> WARN_ON(shmem->base.import_attach);
>
> dma_resv_lock(shmem->base.resv, NULL);
> - ret = drm_gem_shmem_get_pages(shmem);
> - WARN_ON_ONCE(ret != 0);
> +
> + if (drm_gem_shmem_get_pages(shmem))
> + shmem->pages_use_count++;
> +
> + drm_gem_shmem_update_pages_state(shmem);
> dma_resv_unlock(shmem->base.resv);
>
> drm_gem_vm_open(vma);
> @@ -583,6 +787,8 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_mmap);
> void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
> struct drm_printer *p, unsigned int indent)
> {
> + drm_printf_indent(p, indent, "eviction_enabled=%d\n", shmem->eviction_enabled);
> + drm_printf_indent(p, indent, "purge_enabled=%d\n", shmem->purge_enabled);
> drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
>
> if (shmem->base.import_attach)
> @@ -592,7 +798,9 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
> drm_printf_indent(p, indent, "vmap_use_count=%u\n",
> shmem->vmap_use_count);
>
> + drm_printf_indent(p, indent, "evicted=%d\n", shmem->evicted);
> drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
> + drm_printf_indent(p, indent, "madv=%d\n", shmem->madv);
> }
> EXPORT_SYMBOL(drm_gem_shmem_print_info);
>
> @@ -667,6 +875,8 @@ struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem)
>
> shmem->sgt = sgt;
>
> + drm_gem_shmem_update_pages_state(shmem);
> +
> dma_resv_unlock(shmem->base.resv);
>
> return sgt;
> @@ -717,6 +927,250 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
>
> +static struct drm_gem_shmem_shrinker *
> +to_drm_shrinker(struct shrinker *shrinker)
> +{
> + return container_of(shrinker, struct drm_gem_shmem_shrinker, base);
> +}
> +
> +static unsigned long
> +drm_gem_shmem_shrinker_count_objects(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + struct drm_gem_shmem_shrinker *gem_shrinker = to_drm_shrinker(shrinker);
> + struct drm_gem_shmem_object *shmem;
> + unsigned long count = 0;
> +
> + if (!mutex_trylock(&gem_shrinker->lock))
> + return 0;
> +
> + list_for_each_entry(shmem, &gem_shrinker->lru_evictable, madv_list) {
> + count += shmem->base.size;
> +
> + if (count >= SHRINK_EMPTY)
> + break;
> + }
> +
> + mutex_unlock(&gem_shrinker->lock);

As I mentioned on other thread, count_objects, being approximate but
lockless and fast is the important thing. Otherwise when you start
hitting the shrinker on many threads, you end up serializing them all,
even if you have no pages to return to the system at that point.

> +
> + if (count >= SHRINK_EMPTY)
> + return SHRINK_EMPTY - 1;
> +
> + return count ?: SHRINK_EMPTY;
> +}
> +
> +int drm_gem_shmem_evict(struct drm_gem_shmem_object *shmem)
> +{
> + WARN_ON(!drm_gem_shmem_is_evictable(shmem));
> + WARN_ON(shmem->evicted);
> +
> + drm_gem_shmem_unpin_pages(shmem);
> +
> + shmem->evicted = true;
> + drm_gem_shmem_update_pages_state(shmem);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_evict);
> +
> +int drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem)
> +{
> + struct drm_gem_object *obj = &shmem->base;
> +
> + WARN_ON(!drm_gem_shmem_is_purgeable(shmem));
> +
> + drm_gem_shmem_unpin_pages(shmem);
> + drm_gem_free_mmap_offset(obj);
> +
> + /* Our goal here is to return as much of the memory as
> + * is possible back to the system as we are called from OOM.
> + * To do this we must instruct the shmfs to drop all of its
> + * backing pages, *now*.
> + */
> + shmem_truncate_range(file_inode(obj->filp), 0, (loff_t)-1);
> +
> + invalidate_mapping_pages(file_inode(obj->filp)->i_mapping, 0, (loff_t)-1);
> +
> + shmem->madv = -1;
> + shmem->evicted = false;
> + drm_gem_shmem_update_pages_state(shmem);
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_purge);
> +
> +static unsigned long
> +drm_gem_shmem_shrinker_run_objects_scan(struct shrinker *shrinker,
> + unsigned long nr_to_scan,
> + bool *lock_contention,
> + bool evict)
> +{
> + struct drm_gem_shmem_shrinker *gem_shrinker = to_drm_shrinker(shrinker);
> + struct drm_gem_shmem_object *shmem;
> + struct list_head still_in_list;
> + struct drm_gem_object *obj;
> + unsigned long freed = 0;
> + size_t page_count;
> + int err;
> +
> + INIT_LIST_HEAD(&still_in_list);
> +
> + mutex_lock(&gem_shrinker->lock);
> +
> + while (freed < nr_to_scan) {
> + shmem = list_first_entry_or_null(&gem_shrinker->lru_evictable,
> + typeof(*shmem), madv_list);
> + if (!shmem)
> + break;
> +
> + obj = &shmem->base;
> + page_count = obj->size >> PAGE_SHIFT;
> + list_move_tail(&shmem->madv_list, &still_in_list);
> +
> + if (evict) {
> + if (!drm_gem_shmem_is_evictable(shmem) ||
> + get_nr_swap_pages() < page_count)
> + continue;
> + } else {
> + if (!drm_gem_shmem_is_purgeable(shmem))
> + continue;
> + }
> +
> + /*
> + * If it's in the process of being freed, gem_object->free()
> + * may be blocked on lock waiting to remove it. So just
> + * skip it.
> + */
> + if (!kref_get_unless_zero(&obj->refcount))
> + continue;
> +
> + mutex_unlock(&gem_shrinker->lock);
> +
> + /* prevent racing with job-submission code paths */
> + if (!dma_resv_trylock(obj->resv)) {
> + *lock_contention |= true;
> + goto shrinker_lock;
> + }
> +
> + /* prevent racing with the dma-buf importing/exporting */
> + if (!mutex_trylock(&gem_shrinker->dev->object_name_lock)) {
> + *lock_contention |= true;
> + goto resv_unlock;
> + }

I'm not sure this is a good idea to serialize on object_name_lock.
Purgeable buffers should never be shared (imported or exported). So
at best you are avoiding evicting and immediately swapping back in, in
a rare case, at the cost of serializing multiple threads trying to
reclaim pages in parallel.

BR,
-R

> +
> + /* check whether h/w uses this object */
> + if (!dma_resv_test_signaled(obj->resv, DMA_RESV_USAGE_WRITE))
> + goto object_name_unlock;
> +
> + /* re-check whether eviction status hasn't changed */
> + if (!drm_gem_shmem_is_evictable(shmem) &&
> + !drm_gem_shmem_is_purgeable(shmem))
> + goto object_name_unlock;
> +
> + err = shmem->evict(shmem);
> + if (!err)
> + freed += obj->size >> PAGE_SHIFT;
> +
> +object_name_unlock:
> + mutex_unlock(&gem_shrinker->dev->object_name_lock);
> +resv_unlock:
> + dma_resv_unlock(obj->resv);
> +shrinker_lock:
> + drm_gem_object_put(&shmem->base);
> + mutex_lock(&gem_shrinker->lock);
> + }
> +
> + list_splice_tail(&still_in_list, &gem_shrinker->lru_evictable);
> +
> + mutex_unlock(&gem_shrinker->lock);
> +
> + return freed;
> +}
> +
> +static unsigned long
> +drm_gem_shmem_shrinker_scan_objects(struct shrinker *shrinker,
> + struct shrink_control *sc)
> +{
> + unsigned long nr_to_scan = sc->nr_to_scan;
> + bool lock_contention = false;
> + unsigned long freed;
> +
> + /* purge as many objects as we can */
> + freed = drm_gem_shmem_shrinker_run_objects_scan(shrinker, nr_to_scan,
> + &lock_contention, false);
> +
> + /* evict as many objects as we can */
> + if (freed < nr_to_scan)
> + freed += drm_gem_shmem_shrinker_run_objects_scan(shrinker,
> + nr_to_scan - freed,
> + &lock_contention,
> + true);
> +
> + return (!freed && !lock_contention) ? SHRINK_STOP : freed;
> +}
> +
> +/**
> + * drm_gem_shmem_shrinker_register() - Register shmem shrinker
> + * @dev: DRM device
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_shmem_shrinker_register(struct drm_device *dev)
> +{
> + struct drm_gem_shmem_shrinker *gem_shrinker;
> + int err;
> +
> + if (WARN_ON(dev->shmem_shrinker))
> + return -EBUSY;
> +
> + gem_shrinker = kzalloc(sizeof(*gem_shrinker), GFP_KERNEL);
> + if (!gem_shrinker)
> + return -ENOMEM;
> +
> + gem_shrinker->base.count_objects = drm_gem_shmem_shrinker_count_objects;
> + gem_shrinker->base.scan_objects = drm_gem_shmem_shrinker_scan_objects;
> + gem_shrinker->base.seeks = DEFAULT_SEEKS;
> + gem_shrinker->dev = dev;
> +
> + INIT_LIST_HEAD(&gem_shrinker->lru_evictable);
> + INIT_LIST_HEAD(&gem_shrinker->lru_evicted);
> + INIT_LIST_HEAD(&gem_shrinker->lru_pinned);
> + mutex_init(&gem_shrinker->lock);
> +
> + dev->shmem_shrinker = gem_shrinker;
> +
> + err = register_shrinker(&gem_shrinker->base);
> + if (err) {
> + dev->shmem_shrinker = NULL;
> + kfree(gem_shrinker);
> + return err;
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_shrinker_register);
> +
> +/**
> + * drm_gem_shmem_shrinker_unregister() - Unregister shmem shrinker
> + * @dev: DRM device
> + */
> +void drm_gem_shmem_shrinker_unregister(struct drm_device *dev)
> +{
> + struct drm_gem_shmem_shrinker *gem_shrinker = dev->shmem_shrinker;
> +
> + if (gem_shrinker) {
> + unregister_shrinker(&gem_shrinker->base);
> + WARN_ON(!list_empty(&gem_shrinker->lru_evictable));
> + WARN_ON(!list_empty(&gem_shrinker->lru_evicted));
> + WARN_ON(!list_empty(&gem_shrinker->lru_pinned));
> + mutex_destroy(&gem_shrinker->lock);
> + dev->shmem_shrinker = NULL;
> + kfree(gem_shrinker);
> + }
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_shrinker_unregister);
> +
> MODULE_DESCRIPTION("DRM SHMEM memory-management helpers");
> MODULE_IMPORT_NS(DMA_BUF);
> MODULE_LICENSE("GPL v2");
> diff --git a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> index a4bedfeb2ec4..7cc32556f908 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_gem_shrinker.c
> @@ -15,6 +15,13 @@
> #include "panfrost_gem.h"
> #include "panfrost_mmu.h"
>
> +static bool panfrost_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
> +{
> + return (shmem->madv > 0) &&
> + !shmem->pages_pin_count && shmem->sgt &&
> + !shmem->base.dma_buf && !shmem->base.import_attach;
> +}
> +
> static unsigned long
> panfrost_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
> {
> @@ -27,7 +34,7 @@ panfrost_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc
> return 0;
>
> list_for_each_entry(shmem, &pfdev->shrinker_list, madv_list) {
> - if (drm_gem_shmem_is_purgeable(shmem))
> + if (panfrost_gem_shmem_is_purgeable(shmem))
> count += shmem->base.size >> PAGE_SHIFT;
> }
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> index b2d93cb12ebf..81bacc7e1873 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> @@ -89,6 +89,7 @@ struct virtio_gpu_object {
> uint32_t hw_res_handle;
> bool dumb;
> bool created;
> + bool detached;
> bool host3d_blob, guest_blob;
> uint32_t blob_mem, blob_flags;
>
> @@ -453,6 +454,8 @@ int virtio_gpu_object_create(struct virtio_gpu_device *vgdev,
>
> bool virtio_gpu_is_shmem(struct virtio_gpu_object *bo);
>
> +int virtio_gpu_reattach_shmem_object(struct virtio_gpu_object *bo);
> +
> int virtio_gpu_resource_id_get(struct virtio_gpu_device *vgdev,
> uint32_t *resid);
> /* virtgpu_prime.c */
> diff --git a/include/drm/drm_device.h b/include/drm/drm_device.h
> index 9923c7a6885e..929546cad894 100644
> --- a/include/drm/drm_device.h
> +++ b/include/drm/drm_device.h
> @@ -16,6 +16,7 @@ struct drm_vblank_crtc;
> struct drm_vma_offset_manager;
> struct drm_vram_mm;
> struct drm_fb_helper;
> +struct drm_gem_shmem_shrinker;
>
> struct inode;
>
> @@ -277,6 +278,9 @@ struct drm_device {
> /** @vram_mm: VRAM MM memory manager */
> struct drm_vram_mm *vram_mm;
>
> + /** @shmem_shrinker: SHMEM GEM memory shrinker */
> + struct drm_gem_shmem_shrinker *shmem_shrinker;
> +
> /**
> * @switch_power_state:
> *
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index 9a8983ee8abe..62c640678a91 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -6,6 +6,7 @@
> #include <linux/fs.h>
> #include <linux/mm.h>
> #include <linux/mutex.h>
> +#include <linux/shrinker.h>
>
> #include <drm/drm_file.h>
> #include <drm/drm_gem.h>
> @@ -15,6 +16,7 @@
> struct dma_buf_attachment;
> struct drm_mode_create_dumb;
> struct drm_printer;
> +struct drm_device;
> struct sg_table;
>
> /**
> @@ -39,12 +41,21 @@ struct drm_gem_shmem_object {
> */
> unsigned int pages_use_count;
>
> + /**
> + * @pages_pin_count:
> + *
> + * Reference count on the pinned pages table.
> + * The pages can be evicted by memory shrinker
> + * when the count reaches zero.
> + */
> + unsigned int pages_pin_count;
> +
> /**
> * @madv: State for madvise
> *
> * 0 is active/inuse.
> + * 1 is not-needed/can-be-purged
> * A negative value is the object is purged.
> - * Positive values are driver specific and not used by the helpers.
> */
> int madv;
>
> @@ -91,6 +102,39 @@ struct drm_gem_shmem_object {
> * @map_wc: map object write-combined (instead of using shmem defaults).
> */
> bool map_wc;
> +
> + /**
> + * @eviction_enabled:
> + *
> + * The shmem pages can be evicted only if @eviction_enabled is set to true.
> + * Used internally by memory shrinker.
> + */
> + bool eviction_enabled;
> +
> + /**
> + * @purge_enabled:
> + *
> + * The shmem pages can be purged only if @purge_enabled is set to true.
> + * Used internally by memory shrinker.
> + */
> + bool purge_enabled;
> +
> + /**
> + * @evicted: True if shmem pages are evicted by the memory shrinker.
> + * Used internally by memory shrinker.
> + */
> + bool evicted;
> +
> + /**
> + * @evict:
> + *
> + * Invoked by shmem shrinker before evicting shmem GEM from memory.
> + * GEM's DMA reservation is kept locked by the shrinker. This is
> + * optional callback that should be specified by drivers.
> + *
> + * Returns 0 on success, or -errno on error.
> + */
> + int (*evict)(struct drm_gem_shmem_object *shmem);
> };
>
> #define to_drm_gem_shmem_obj(obj) \
> @@ -110,14 +154,21 @@ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct
>
> int drm_gem_shmem_madvise(struct drm_gem_shmem_object *shmem, int madv);
>
> +int drm_gem_shmem_set_purgeable(struct drm_gem_shmem_object *shmem);
> +int drm_gem_shmem_set_evictable(struct drm_gem_shmem_object *shmem);
> +
> static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
> {
> - return (shmem->madv > 0) &&
> - !shmem->vmap_use_count && shmem->sgt &&
> - !shmem->base.dma_buf && !shmem->base.import_attach;
> + return (shmem->madv > 0) && shmem->evict &&
> + shmem->purge_enabled && shmem->pages_use_count &&
> + !shmem->pages_pin_count && !shmem->base.dma_buf &&
> + !shmem->base.import_attach && (shmem->sgt || shmem->evicted);
> }
>
> -void drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem);
> +int drm_gem_shmem_swap_in(struct drm_gem_shmem_object *shmem);
> +
> +int drm_gem_shmem_evict(struct drm_gem_shmem_object *shmem);
> +int drm_gem_shmem_purge(struct drm_gem_shmem_object *shmem);
>
> struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_shmem_object *shmem);
> struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem);
> @@ -260,6 +311,32 @@ static inline int drm_gem_shmem_object_mmap(struct drm_gem_object *obj, struct v
> return drm_gem_shmem_mmap(shmem, vma);
> }
>
> +/**
> + * struct drm_gem_shmem_shrinker - Generic memory shrinker for shmem GEMs
> + */
> +struct drm_gem_shmem_shrinker {
> + /** @base: Shrinker for purging shmem GEM objects */
> + struct shrinker base;
> +
> + /** @lock: Protects @lru_* */
> + struct mutex lock;
> +
> + /** @lru_pinned: List of pinned shmem GEM objects */
> + struct list_head lru_pinned;
> +
> + /** @lru_evictable: List of shmem GEM objects to be evicted */
> + struct list_head lru_evictable;
> +
> + /** @lru_evicted: List of evicted shmem GEM objects */
> + struct list_head lru_evicted;
> +
> + /** @dev: DRM device that uses this shrinker */
> + struct drm_device *dev;
> +};
> +
> +int drm_gem_shmem_shrinker_register(struct drm_device *dev);
> +void drm_gem_shmem_shrinker_unregister(struct drm_device *dev);
> +
> /*
> * Driver ops
> */
> --
> 2.35.3
>