When we are called to relieve mempressue via the shrinker, the only way
we can make progress is either by discarding unwanted pages (those
objects that userspace has marked MADV_DONTNEED) or by reclaiming the
dirty objects via swap. As we know that is the only way to make further
progress, we can initiate the writeback as we invalidate the objects.
This means the objects we put onto the inactive anon lru list are
already marked for reclaim+writeback and so will trigger a wait upon the
writeback inside direct reclaim, greatly improving the success rate of
direct reclaim on i915 objects.
The corollary is that we may start a slow swap on opportunistic
mempressure from the likes of the compaction + migration kthreads. This
is limited by those threads only being allowed to shrink idle pages, but
also that if we reactivate the page before it is swapped out by gpu
activity, we only page the cost of repinning the page. The cost is most
felt when an object is reused after mempressure, which hopefully
excludes the latency sensitive tasks (as we are just extending the
impact of swap thrashing to them).
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
---
drivers/gpu/drm/i915/i915_drv.h | 2 +-
drivers/gpu/drm/i915/i915_gem.c | 27 ++--------------
drivers/gpu/drm/i915/i915_gem_shrinker.c | 55 +++++++++++++++++++++++++++++++-
3 files changed, 57 insertions(+), 27 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index c31c0cfe5c20..33ffec1e6c90 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3321,7 +3321,7 @@ enum i915_mm_subclass { /* lockdep subclass for obj->mm.lock */
void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
enum i915_mm_subclass subclass);
-void __i915_gem_object_invalidate(struct drm_i915_gem_object *obj);
+void __i915_gem_object_truncate(struct drm_i915_gem_object *obj);
enum i915_map_type {
I915_MAP_WB = 0,
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 845df6067e90..8cb811519db1 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2176,8 +2176,7 @@ i915_gem_mmap_gtt_ioctl(struct drm_device *dev, void *data,
}
/* Immediately discard the backing storage */
-static void
-i915_gem_object_truncate(struct drm_i915_gem_object *obj)
+void __i915_gem_object_truncate(struct drm_i915_gem_object *obj)
{
i915_gem_object_free_mmap_offset(obj);
@@ -2194,28 +2193,6 @@ i915_gem_object_truncate(struct drm_i915_gem_object *obj)
obj->mm.pages = ERR_PTR(-EFAULT);
}
-/* Try to discard unwanted pages */
-void __i915_gem_object_invalidate(struct drm_i915_gem_object *obj)
-{
- struct address_space *mapping;
-
- lockdep_assert_held(&obj->mm.lock);
- GEM_BUG_ON(obj->mm.pages);
-
- switch (obj->mm.madv) {
- case I915_MADV_DONTNEED:
- i915_gem_object_truncate(obj);
- case __I915_MADV_PURGED:
- return;
- }
-
- if (obj->base.filp == NULL)
- return;
-
- mapping = obj->base.filp->f_mapping,
- invalidate_mapping_pages(mapping, 0, (loff_t)-1);
-}
-
static void
i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj,
struct sg_table *pages)
@@ -4215,7 +4192,7 @@ i915_gem_madvise_ioctl(struct drm_device *dev, void *data,
/* if the object is no longer attached, discard its backing storage */
if (obj->mm.madv == I915_MADV_DONTNEED && !obj->mm.pages)
- i915_gem_object_truncate(obj);
+ __i915_gem_object_truncate(obj);
args->retained = obj->mm.madv != __I915_MADV_PURGED;
mutex_unlock(&obj->mm.lock);
diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
index 58f27369183c..026500ad6d35 100644
--- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
+++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
@@ -122,6 +122,59 @@ static bool unsafe_drop_pages(struct drm_i915_gem_object *obj)
return !READ_ONCE(obj->mm.pages);
}
+static void __start_writeback(struct drm_i915_gem_object *obj)
+{
+ struct address_space *mapping;
+ struct writeback_control wbc = {
+ .sync_mode = WB_SYNC_NONE,
+ .nr_to_write = SWAP_CLUSTER_MAX,
+ .range_start = 0,
+ .range_end = LLONG_MAX,
+ .for_reclaim = 1,
+ };
+ unsigned long i;
+
+ lockdep_assert_held(&obj->mm.lock);
+ GEM_BUG_ON(obj->mm.pages);
+
+ switch (obj->mm.madv) {
+ case I915_MADV_DONTNEED:
+ __i915_gem_object_truncate(obj);
+ case __I915_MADV_PURGED:
+ return;
+ }
+
+ if (!obj->base.filp)
+ return;
+
+ /* Force any other users of this object to refault */
+ mapping = obj->base.filp->f_mapping;
+ unmap_mapping_range(mapping, 0, (loff_t)-1, 0);
+
+ /* Begin writeback on each dirty page */
+ for (i = 0; i < obj->base.size >> PAGE_SHIFT; i++) {
+ struct page *page;
+
+ page = find_lock_entry(mapping, i);
+ if (radix_tree_exceptional_entry(page))
+ continue;
+
+ if (!page_mapped(page) && clear_page_dirty_for_io(page)) {
+ int ret;
+
+ SetPageReclaim(page);
+ ret = mapping->a_ops->writepage(page, &wbc);
+ if (!PageWriteback(page))
+ ClearPageReclaim(page);
+ if (!ret)
+ goto put;
+ }
+ unlock_page(page);
+put:
+ put_page(page);
+ }
+}
+
/**
* i915_gem_shrink - Shrink buffer object caches
* @dev_priv: i915 device
@@ -234,7 +287,7 @@ i915_gem_shrink(struct drm_i915_private *dev_priv,
mutex_lock_nested(&obj->mm.lock,
I915_MM_SHRINKER);
if (!obj->mm.pages) {
- __i915_gem_object_invalidate(obj);
+ __start_writeback(obj);
list_del_init(&obj->global_link);
count += obj->base.size >> PAGE_SHIFT;
}
--
2.11.0
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