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

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

Am 05.06.22 um 18:47 schrieb Daniel Vetter:
> On Fri, 27 May 2022 at 01:55, 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>
> So I guess I get a price for being blind since forever, because this
> thing existed since at least 2013. I just stumbled over
> llist_lru.[hc], a purpose built list helper for shrinkers. I think we
> should try to adopt that so that our gpu shrinkers look more like
> shrinkers for everything else.

What the heck are you talking about?

I can't find any llist_lru.[hc] in the linux kernel sources.

Christian.

>
> Apologies for this, since I fear this might cause a bit of churn.
> Hopefully it's all contained to the list manipulation code in shmem
> helpers, I don't think this should leak any further.
> -Daniel
>
>> ---
>>   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);
>> +
>> +       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;
>> +               }
>> +
>> +               /* 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
>>
>