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References: <20220526235040.678984-1-dmitry.osipenko@collabora.com> <20220526235040.678984-18-dmitry.osipenko@collabora.com>
In-Reply-To: <20220526235040.678984-18-dmitry.osipenko@collabora.com>
From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Sun, 5 Jun 2022 18:47:46 +0200
Message-ID: <CAKMK7uHQ+iMkXtrsCWiJL9X1AM9Xkq-wNmj=hhfnenf0r9717g@mail.gmail.com>
Subject: Re: [PATCH v6 17/22] drm/shmem-helper: Add generic memory shrinker
To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc:     David Airlie <airlied@linux.ie>, Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>,
        Daniel Almeida <daniel.almeida@collabora.com>,
        Gert Wollny <gert.wollny@collabora.com>,
        Gustavo Padovan <gustavo.padovan@collabora.com>,
        Daniel Stone <daniel@fooishbar.org>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Rob Herring <robh@kernel.org>,
        Steven Price <steven.price@arm.com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
        Rob Clark <robdclark@gmail.com>,
        Emil Velikov <emil.l.velikov@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Qiang Yu <yuq825@gmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Tomasz Figa <tfiga@chromium.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        Dmitry Osipenko <digetx@gmail.com>,
        linux-tegra@vger.kernel.org, linux-media@vger.kernel.org,
        linaro-mm-sig@lists.linaro.org, amd-gfx@lists.freedesktop.org,
        intel-gfx@lists.freedesktop.org, kernel@collabora.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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.

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
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch