From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> On a long run of more than 2-3 days, physical memory tends to get fragmented severely, which considerably slows down the system. In such a scenario, the shrinker is also unable to help as lack of memory is not the actual problem, since it has been observed that there are enough free pages of 0 order. This also manifests itself when an indiviual zone in the mm runs out of pages and if we cannot migrate pages between zones, the kernel hits an out-of-memory even though there are free pages (and often all of swap) available. To address the issue of external fragementation, kernel does a compaction (which involves migration of pages) but it's efficacy depends upon how many pages are marked as MOVABLE, as only those pages can be migrated. Currently the backing pages for GPU buffers are allocated from shmemfs with GFP_RECLAIMABLE flag, in units of 4KB pages. In the case of limited swap space, it may not be possible always to reclaim or swap-out pages of all the inactive objects, to make way for free space allowing formation of higher order groups of physically-contiguous pages on compaction. Just marking the GPU pages as MOVABLE will not suffice, as i915.ko has to pin the pages if they are in use by GPU, which will prevent their migration. So the migratepage callback in shmem is also hooked up to get a notification when kernel initiates the page migration. On the notification, i915.ko appropriately unpin the pages. With this we can effectively mark the GPU pages as MOVABLE and hence mitigate the fragmentation problem. v2: - Rename the migration routine to gem_shrink_migratepage, move it to the shrinker file, and use the existing constructs (Chris) - To cleanup, add a new helper function to encapsulate all page migration skip conditions (Chris) - Add a new local helper function in shrinker file, for dropping the backing pages, and call the same from gem_shrink() also (Chris) v3: - Fix/invert the check on the return value of unsafe_drop_pages (Chris) v4: - Minor tidy v5: - Fix unsafe usage of unsafe_drop_pages() - Rebase onto vmap-notifier Testcase: igt/gem_shrink Bugzilla: (e.g.) https://bugs.freedesktop.org/show_bug.cgi?id=90254 Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: linux-mm@xxxxxxxxx Signed-off-by: Sourab Gupta <sourab.gupta@xxxxxxxxx> Signed-off-by: Akash Goel <akash.goel@xxxxxxxxx> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/i915_drv.h | 2 + drivers/gpu/drm/i915/i915_gem.c | 9 ++- drivers/gpu/drm/i915/i915_gem_shrinker.c | 134 +++++++++++++++++++++++++++++++ 3 files changed, 144 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index 4735b417..7f2717b 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -1357,6 +1357,8 @@ struct intel_l3_parity { }; struct i915_gem_mm { + struct shmem_dev_info shmem_info; + /** Memory allocator for GTT stolen memory */ struct drm_mm stolen; /** Protects the usage of the GTT stolen memory allocator. This is diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 1f995ce..f0d4ce7 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -2164,6 +2164,7 @@ void __i915_gem_object_invalidate(struct drm_i915_gem_object *obj) if (obj->mm.madv == I915_MADV_WILLNEED) mark_page_accessed(page); + set_page_private(page, 0); put_page(page); } obj->mm.dirty = false; @@ -2310,6 +2311,7 @@ static unsigned int swiotlb_max_size(void) sg->length += PAGE_SIZE; } last_pfn = page_to_pfn(page); + set_page_private(page, (unsigned long)obj); /* Check that the i965g/gm workaround works. */ WARN_ON((gfp & __GFP_DMA32) && (last_pfn >= 0x00100000UL)); @@ -2334,8 +2336,10 @@ static unsigned int swiotlb_max_size(void) err_pages: sg_mark_end(sg); - for_each_sgt_page(page, sgt_iter, st) + for_each_sgt_page(page, sgt_iter, st) { + set_page_private(page, 0); put_page(page); + } sg_free_table(st); kfree(st); @@ -4185,6 +4189,8 @@ struct drm_i915_gem_object * goto fail; mask = GFP_HIGHUSER | __GFP_RECLAIMABLE; + if (IS_ENABLED(MIGRATION)) + mask |= __GFP_MOVABLE; if (IS_CRESTLINE(dev_priv) || IS_BROADWATER(dev_priv)) { /* 965gm cannot relocate objects above 4GiB. */ mask &= ~__GFP_HIGHMEM; @@ -4193,6 +4199,7 @@ struct drm_i915_gem_object * mapping = obj->base.filp->f_mapping; mapping_set_gfp_mask(mapping, mask); + shmem_set_dev_info(mapping, &dev_priv->mm.shmem_info); i915_gem_object_init(obj, &i915_gem_object_ops); diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c index a6fc1bd..2862523 100644 --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c @@ -24,6 +24,7 @@ #include <linux/oom.h> #include <linux/shmem_fs.h> +#include <linux/migrate.h> #include <linux/slab.h> #include <linux/swap.h> #include <linux/pci.h> @@ -473,6 +474,134 @@ struct shrinker_lock_uninterruptible { return NOTIFY_DONE; } +#ifdef CONFIG_MIGRATION +static bool can_migrate_page(struct drm_i915_gem_object *obj) +{ + /* Avoid the migration of page if being actively used by GPU */ + if (i915_gem_object_is_active(obj)) + return false; + + /* Skip the migration for purgeable objects otherwise there + * will be a deadlock when shmem will try to lock the page for + * truncation, which is already locked by the caller before + * migration. + */ + if (obj->mm.madv == I915_MADV_DONTNEED) + return false; + + /* Skip the migration for a pinned object */ + if (atomic_read(&obj->mm.pages_pin_count) > obj->bind_count) + return false; + + if (any_vma_pinned(obj)) + return false; + + return true; +} + +static int do_migrate_page(struct drm_i915_gem_object *obj) +{ + struct drm_i915_private *dev_priv = to_i915(obj->base.dev); + int ret = 0; + + if (!can_migrate_page(obj)) + return -EBUSY; + + /* HW access would be required for a GGTT bound object, for which + * device has to be kept awake. But a deadlock scenario can arise if + * the attempt is made to resume the device, when either a suspend + * or a resume operation is already happening concurrently from some + * other path and that only also triggers compaction. So only unbind + * if the device is currently awake. + */ + if (!intel_runtime_pm_get_if_in_use(dev_priv)) + return -EBUSY; + + i915_gem_object_get(obj); + if (!unsafe_drop_pages(obj)) + ret = -EBUSY; + i915_gem_object_put(obj); + + intel_runtime_pm_put(dev_priv); + return ret; +} + +static int i915_gem_shrinker_migratepage(struct address_space *mapping, + struct page *newpage, + struct page *page, + enum migrate_mode mode, + void *dev_priv_data) +{ + struct drm_i915_private *dev_priv = dev_priv_data; + struct shrinker_lock_uninterruptible slu; + int ret; + + /* + * Clear the private field of the new target page as it could have a + * stale value in the private field. Otherwise later on if this page + * itself gets migrated, without getting referred by the Driver + * in between, the stale value would cause the i915_migratepage + * function to go for a toss as object pointer is derived from it. + * This should be safe since at the time of migration, private field + * of the new page (which is actually an independent free 4KB page now) + * should be like a don't care for the kernel. + */ + set_page_private(newpage, 0); + + if (!page_private(page)) + goto migrate; + + /* + * Check the page count, if Driver also has a reference then it should + * be more than 2, as shmem will have one reference and one reference + * would have been taken by the migration path itself. So if reference + * is <=2, we can directly invoke the migration function. + */ + if (page_count(page) <= 2) + goto migrate; + + /* + * Use trylock here, with a timeout, for struct_mutex as + * otherwise there is a possibility of deadlock due to lock + * inversion. This path, which tries to migrate a particular + * page after locking that page, can race with a path which + * truncate/purge pages of the corresponding object (after + * acquiring struct_mutex). Since page truncation will also + * try to lock the page, a scenario of deadlock can arise. + */ + if (!i915_gem_shrinker_lock_uninterruptible(dev_priv, &slu, 10)) + return -EBUSY; + + ret = 0; + if (!PageSwapCache(page) && page_private(page)) { + struct drm_i915_gem_object *obj = + (struct drm_i915_gem_object *)page_private(page); + + ret = do_migrate_page(obj); + } + + i915_gem_shrinker_unlock_uninterruptible(dev_priv, &slu); + if (ret) + return ret; + + /* + * Ideally here we don't expect the page count to be > 2, as driver + * would have dropped its reference, but occasionally it has been seen + * coming as 3 & 4. This leads to a situation of unexpected page count, + * causing migration failure, with -EGAIN error. This then leads to + * multiple attempts by the kernel to migrate the same set of pages. + * And sometimes the repeated attempts proves detrimental for stability. + * Also since we don't know who is the other owner, and for how long its + * gonna keep the reference, its better to return -EBUSY. + */ + if (page_count(page) > 2) + return -EBUSY; + +migrate: + return migrate_page(mapping, newpage, page, mode); +} +#endif + /** * i915_gem_shrinker_init - Initialize i915 shrinker * @dev_priv: i915 device @@ -491,6 +620,11 @@ void i915_gem_shrinker_init(struct drm_i915_private *dev_priv) dev_priv->mm.vmap_notifier.notifier_call = i915_gem_shrinker_vmap; WARN_ON(register_vmap_purge_notifier(&dev_priv->mm.vmap_notifier)); + + dev_priv->mm.shmem_info.private_data = dev_priv; +#ifdef CONFIG_MIGRATION + dev_priv->mm.shmem_info.migratepage = i915_gem_shrinker_migratepage; +#endif } /** -- 1.9.2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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