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* [PATCH v7] cgroup/dmem: implement dmem.high soft limit with proactive reclaim
@ 2026-07-09  4:02 Qiliang Yuan
  2026-07-09  5:44 ` Matthew Brost
  0 siblings, 1 reply; 4+ messages in thread
From: Qiliang Yuan @ 2026-07-09  4:02 UTC (permalink / raw)
  To: Christian Koenig, Huang Rui, Matthew Auld, Matthew Brost,
	Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
	Simona Vetter, Tejun Heo, Johannes Weiner, Michal Koutný,
	Natalie Vock
  Cc: Michal Hocko, Roman Gushchin, Shakeel Butt, Muchun Song,
	dri-devel, linux-kernel, cgroups, linux-mm, Qiliang Yuan, Jing Wu

The dmem cgroup v2 controller currently only provides a hard "max"
limit, which causes immediate allocation failures when a cgroup's
device memory usage reaches its quota.  GPU-bound AI workloads need
smoother over-subscription support: a soft limit that provides
backpressure through reclaim before the hard limit is reached.

Implement dmem.high as a proper soft limit following the memory.high
semantics: the limit is checked in the charge path on every successful
allocation, and proactive reclaim is triggered when usage crosses the
threshold, rather than waiting for a dmem.max hit to drive eviction.

Expose "high" as a new cgroupfs control file per region via
set_resource_high() and get_resource_high(), initialized to
PAGE_COUNTER_MAX in reset_all_resource_limits().  Like get_resource_max(),
get_resource_high() returns PAGE_COUNTER_MAX when the pool is NULL.

Extend dmem_cgroup_try_charge() with a ret_over_high_pool output
parameter.  On a successful charge, if the pool's usage now exceeds its
dmem.high threshold, ret_over_high_pool is set so the caller can
trigger proactive reclaim.  Propagate this signal through
ttm_resource_alloc() up to ttm_bo_alloc_resource().

Add ttm_bo_proactive_evict_high() in TTM, which walks the LRU and
evicts one BO from the over-limit cgroup (using the existing try_high
logic in dmem_cgroup_state_evict_valuable()).  This is best-effort:
the allocation already succeeded since dmem.high is a soft limit.
A blocking lock is used when a ww_acquire_ctx ticket is available,
trylock otherwise.

Remove the try_high first pass from ttm_bo_evict_alloc(): that pass
tied the interface semantics to a specific eviction ordering detail
rather than a proper soft limit.  Proactive reclaim in the charge
path is the correct place to enforce the soft limit.

Co-developed-by: Qiliang Yuan <yuanql9@chinatelecom.cn>
Signed-off-by: Qiliang Yuan <yuanql9@chinatelecom.cn>
Signed-off-by: Jing Wu <realwujing@gmail.com>
---
Implement dmem.high as a proper soft limit for the dmem cgroup v2
controller, following memory.high semantics: the limit is checked in
the charge path on every successful allocation, and proactive reclaim
is triggered when usage crosses the threshold.

The dmem cgroup currently only supports a hard "max" limit, which causes
allocation failures for GPU-bound workloads.  A soft limit enables
smoother over-subscription by providing backpressure through reclaim
before the hard limit is reached.

The implementation extends dmem_cgroup_try_charge() with a
ret_over_high_pool output parameter that signals callers when a
successful charge pushes usage above the dmem.high threshold.
ttm_resource_alloc() propagates this signal up to
ttm_bo_alloc_resource(), where ttm_bo_proactive_evict_high() evicts
one BO from the over-limit cgroup on a best-effort basis.
---
V6 -> V7:
- Replace prioritized eviction (eviction-time ordering) with proactive
  reclaim (charge-time enforcement): dmem.high is now checked in
  dmem_cgroup_try_charge() on every successful allocation, matching
  memory.high semantics as requested by Tejun Heo.
- Add ret_over_high_pool output parameter to dmem_cgroup_try_charge()
  to signal callers when a successful charge crosses the high threshold.
- Add ttm_bo_proactive_evict_high() to evict one BO from the over-limit
  cgroup on each allocation that crosses dmem.high (best-effort; the
  allocation already succeeded since dmem.high is a soft limit).
- Remove the try_high first pass from ttm_bo_evict_alloc(): the high
  limit is no longer enforced via eviction ordering in the max path.
- Propagate ret_over_high_pool through ttm_resource_alloc() and update
  all callers (including TTM test files) to pass the new parameter.
- Add Michal Hocko, Roman Gushchin, Shakeel Butt, Muchun Song to Cc
  per Tejun's request for memcg input on soft limit semantics.

V5 -> V6:
- Guard the try_high dereference of test_pool->cnt with a NULL check
  to prevent a kernel panic during global memory pressure eviction
  when a BO has no associated cgroup.
- Make the disabled-cgroup stub for dmem_cgroup_state_evict_valuable()
  return false in try_high mode so the stub does not incorrectly
  enable Pass 1 when CONFIG_CGROUP_DMEM=n.

V4 -> V5:
- Restore the original control flow in dmem_cgroup_state_evict_valuable():
  test_pool is no longer dereferenced before the ancestry checks, fixing
  a NULL pointer dereference on BOs without a cgroup.  The limit_pool
  NULL-to-root-cgroup resolution is now performed before the try_high
  block, fixing a panic during global memory pressure eviction.
- Keep the try_high check for limit_pool == test_pool inside the existing
  early-return branch to avoid bypassing the hierarchy constraint check
  that prevents cross-cgroup eviction.
- Use a blocking lock in Pass 1 only when a ticket is available
  (trylock otherwise), addressing the deadlock risk of blocking without
  a valid ww_acquire_ctx.
- Explicitly reset trylock_only to true before Pass 2 so it does not
  inherit Pass 1's blocking behavior.

V3 -> V4:
- Use a blocking lock in Pass 1 instead of trylock to ensure
  over-limit cgroups are penalized even when their BOs are actively
  in use, as requested by Maarten Lankhorst.
- Evaluate the try_high condition before the limit_pool == test_pool
  early-return so that the limit-hitting cgroup's own BOs are also
  filtered by dmem.high.
- Remove the high-priority compensation retry at the start of Pass 3,
  which is no longer needed now that Pass 1 uses a blocking lock.

V2 -> V3:
- Walk the page_counter parent chain in the try_high pass to prevent
  child cgroups from evading the penalty when a parent cgroup exceeds
  its dmem.high limit.
- Check dmem.min protection in the try_high pass to avoid evicting
  BOs below the effective minimum.
- Add a properly-locked high-priority retry at the beginning of Pass 3
  so that actively-used over-limit BOs (which failed trylock in Pass 1)
  are not skipped while innocent cgroups are evicted.
- Fix get_resource_high(NULL) returning 0 instead of PAGE_COUNTER_MAX
  to match the behavior of get_resource_max().

V1 -> V2:
- Replace sleep-on-allocation throttling with prioritized eviction.
- Remove task throttling entirely.
- Add dmem.high cgroupfs control file per region.
- Extend dmem_cgroup_state_evict_valuable() with try_high parameter.
- Refactor ttm_bo_evict_alloc() into a 3-pass eviction strategy.
- Initialize high to PAGE_COUNTER_MAX in reset_all_resource_limits().

v6: https://lore.kernel.org/r/20260531-feature-dmem-high-v6-1-20563ecd6dc7@gmail.com
v5: https://lore.kernel.org/r/20260531-feature-dmem-high-v5-1-1c6c532b26a9@gmail.com
v4: https://lore.kernel.org/r/20260530-feature-dmem-high-v4-1-ee7c6ec1c8da@gmail.com
v3: https://lore.kernel.org/r/20260528-feature-dmem-high-v3-1-c642b34bcb2f@gmail.com
v2: https://lore.kernel.org/r/20260522-feature-dmem-high-v2-1-1d7d4a0fa5da@gmail.com
v1: https://lore.kernel.org/all/20260520-feature-dmem-high-v1-1-97ca0cb7f95a@gmail.com
---
 drivers/gpu/drm/ttm/tests/ttm_bo_test.c          |  18 ++--
 drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c |   4 +-
 drivers/gpu/drm/ttm/tests/ttm_resource_test.c    |   2 +-
 drivers/gpu/drm/ttm/ttm_bo.c                     |  60 ++++++++++---
 drivers/gpu/drm/ttm/ttm_resource.c               |   8 +-
 include/drm/ttm/ttm_resource.h                   |   3 +-
 include/linux/cgroup_dmem.h                      |  15 +++-
 kernel/cgroup/dmem.c                             | 104 +++++++++++++++++++++--
 8 files changed, 179 insertions(+), 35 deletions(-)

diff --git a/drivers/gpu/drm/ttm/tests/ttm_bo_test.c b/drivers/gpu/drm/ttm/tests/ttm_bo_test.c
index f3103307b5df9..7a03f6a04f4e8 100644
--- a/drivers/gpu/drm/ttm/tests/ttm_bo_test.c
+++ b/drivers/gpu/drm/ttm/tests/ttm_bo_test.c
@@ -258,13 +258,13 @@ static void ttm_bo_unreserve_basic(struct kunit *test)
 	bo = ttm_bo_kunit_init(test, test->priv, BO_SIZE, NULL);
 	bo->priority = bo_prio;
 
-	err = ttm_resource_alloc(bo, place, &res1, NULL);
+	err = ttm_resource_alloc(bo, place, &res1, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 
 	bo->resource = res1;
 
 	/* Add a dummy resource to populate LRU */
-	ttm_resource_alloc(bo, place, &res2, NULL);
+	ttm_resource_alloc(bo, place, &res2, NULL, NULL);
 
 	dma_resv_lock(bo->base.resv, NULL);
 	ttm_bo_unreserve(bo);
@@ -300,12 +300,12 @@ static void ttm_bo_unreserve_pinned(struct kunit *test)
 	dma_resv_lock(bo->base.resv, NULL);
 	ttm_bo_pin(bo);
 
-	err = ttm_resource_alloc(bo, place, &res1, NULL);
+	err = ttm_resource_alloc(bo, place, &res1, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	bo->resource = res1;
 
 	/* Add a dummy resource to the pinned list */
-	err = ttm_resource_alloc(bo, place, &res2, NULL);
+	err = ttm_resource_alloc(bo, place, &res2, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	KUNIT_ASSERT_EQ(test,
 			list_is_last(&res2->lru.link, &priv->ttm_dev->unevictable), 1);
@@ -355,7 +355,7 @@ static void ttm_bo_unreserve_bulk(struct kunit *test)
 	ttm_bo_set_bulk_move(bo1, &lru_bulk_move);
 	dma_resv_unlock(bo1->base.resv);
 
-	err = ttm_resource_alloc(bo1, place, &res1, NULL);
+	err = ttm_resource_alloc(bo1, place, &res1, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	bo1->resource = res1;
 
@@ -363,7 +363,7 @@ static void ttm_bo_unreserve_bulk(struct kunit *test)
 	ttm_bo_set_bulk_move(bo2, &lru_bulk_move);
 	dma_resv_unlock(bo2->base.resv);
 
-	err = ttm_resource_alloc(bo2, place, &res2, NULL);
+	err = ttm_resource_alloc(bo2, place, &res2, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	bo2->resource = res2;
 
@@ -401,7 +401,7 @@ static void ttm_bo_fini_basic(struct kunit *test)
 	bo = ttm_bo_kunit_init(test, test->priv, BO_SIZE, NULL);
 	bo->type = ttm_bo_type_device;
 
-	err = ttm_resource_alloc(bo, place, &res, NULL);
+	err = ttm_resource_alloc(bo, place, &res, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	bo->resource = res;
 
@@ -518,7 +518,7 @@ static void ttm_bo_pin_unpin_resource(struct kunit *test)
 
 	bo = ttm_bo_kunit_init(test, test->priv, BO_SIZE, NULL);
 
-	err = ttm_resource_alloc(bo, place, &res, NULL);
+	err = ttm_resource_alloc(bo, place, &res, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	bo->resource = res;
 
@@ -569,7 +569,7 @@ static void ttm_bo_multiple_pin_one_unpin(struct kunit *test)
 
 	bo = ttm_bo_kunit_init(test, test->priv, BO_SIZE, NULL);
 
-	err = ttm_resource_alloc(bo, place, &res, NULL);
+	err = ttm_resource_alloc(bo, place, &res, NULL, NULL);
 	KUNIT_ASSERT_EQ(test, err, 0);
 	bo->resource = res;
 
diff --git a/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c b/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c
index 2db221f6fc3a1..cd40f5b2ab4f1 100644
--- a/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c
+++ b/drivers/gpu/drm/ttm/tests/ttm_bo_validate_test.c
@@ -547,7 +547,7 @@ static void ttm_bo_validate_no_placement_signaled(struct kunit *test)
 
 	ttm_bo_reserve(bo, false, false, NULL);
 
-	err = ttm_resource_alloc(bo, place, &bo->resource, NULL);
+	err = ttm_resource_alloc(bo, place, &bo->resource, NULL, NULL);
 	KUNIT_EXPECT_EQ(test, err, 0);
 	KUNIT_ASSERT_EQ(test, man->usage, size);
 
@@ -604,7 +604,7 @@ static void ttm_bo_validate_no_placement_not_signaled(struct kunit *test)
 	bo = ttm_bo_kunit_init(test, test->priv, size, NULL);
 	bo->type = params->bo_type;
 
-	err = ttm_resource_alloc(bo, place, &bo->resource, NULL);
+	err = ttm_resource_alloc(bo, place, &bo->resource, NULL, NULL);
 	KUNIT_EXPECT_EQ(test, err, 0);
 
 	placement = kunit_kzalloc(test, sizeof(*placement), GFP_KERNEL);
diff --git a/drivers/gpu/drm/ttm/tests/ttm_resource_test.c b/drivers/gpu/drm/ttm/tests/ttm_resource_test.c
index c0e4e35e04426..41fe4d89cd714 100644
--- a/drivers/gpu/drm/ttm/tests/ttm_resource_test.c
+++ b/drivers/gpu/drm/ttm/tests/ttm_resource_test.c
@@ -303,7 +303,7 @@ static void ttm_sys_man_free_basic(struct kunit *test)
 	res = kunit_kzalloc(test, sizeof(*res), GFP_KERNEL);
 	KUNIT_ASSERT_NOT_NULL(test, res);
 
-	ttm_resource_alloc(bo, place, &res, NULL);
+	ttm_resource_alloc(bo, place, &res, NULL, NULL);
 
 	man = ttm_manager_type(priv->devs->ttm_dev, mem_type);
 	man->func->free(man, res);
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bcd76f6bb7f02..bdfcfe5c7d1e2 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -505,6 +505,8 @@ struct ttm_bo_evict_walk {
 
 	/** @limit_pool: Which pool limit we should test against */
 	struct dmem_cgroup_pool_state *limit_pool;
+	/** @try_high: Whether to only evict BO's above the high watermark (first pass) */
+	bool try_high;
 	/** @try_low: Whether we should attempt to evict BO's with low watermark threshold */
 	bool try_low;
 	/** @hit_low: If we cannot evict a bo when @try_low is false (first pass) */
@@ -518,7 +520,8 @@ static s64 ttm_bo_evict_cb(struct ttm_lru_walk *walk, struct ttm_buffer_object *
 	s64 lret;
 
 	if (!dmem_cgroup_state_evict_valuable(evict_walk->limit_pool, bo->resource->css,
-					      evict_walk->try_low, &evict_walk->hit_low))
+					      evict_walk->try_high, evict_walk->try_low,
+					      &evict_walk->hit_low))
 		return 0;
 
 	if (bo->pin_count || !bo->bdev->funcs->eviction_valuable(bo, evict_walk->place))
@@ -538,7 +541,7 @@ static s64 ttm_bo_evict_cb(struct ttm_lru_walk *walk, struct ttm_buffer_object *
 	evict_walk->evicted++;
 	if (evict_walk->res)
 		lret = ttm_resource_alloc(evict_walk->evictor, evict_walk->place,
-					  evict_walk->res, NULL);
+					  evict_walk->res, NULL, NULL);
 	if (lret == 0)
 		return 1;
 out:
@@ -553,6 +556,38 @@ static const struct ttm_lru_walk_ops ttm_evict_walk_ops = {
 	.process_bo = ttm_bo_evict_cb,
 };
 
+/*
+ * Proactive reclaim: evict one BO from a cgroup that exceeds its dmem.high
+ * soft limit.  Called after a successful charge that pushed usage over the
+ * high threshold.  Best-effort; allocation already succeeded (soft limit).
+ */
+static void ttm_bo_proactive_evict_high(struct ttm_device *bdev,
+					struct ttm_resource_manager *man,
+					const struct ttm_place *place,
+					struct ttm_buffer_object *evictor,
+					struct ttm_operation_ctx *ctx,
+					struct ww_acquire_ctx *ticket,
+					struct dmem_cgroup_pool_state *over_high_pool)
+{
+	struct ttm_bo_evict_walk evict_walk = {
+		.walk = {
+			.ops = &ttm_evict_walk_ops,
+			.arg = {
+				.ctx = ctx,
+				.ticket = ticket,
+				.trylock_only = !ticket,
+			}
+		},
+		.place = place,
+		.evictor = evictor,
+		.res = NULL,
+		.limit_pool = over_high_pool,
+		.try_high = true,
+	};
+
+	ttm_lru_walk_for_evict(&evict_walk.walk, bdev, man, 1);
+}
+
 static int ttm_bo_evict_alloc(struct ttm_device *bdev,
 			      struct ttm_resource_manager *man,
 			      const struct ttm_place *place,
@@ -579,29 +614,24 @@ static int ttm_bo_evict_alloc(struct ttm_device *bdev,
 
 	evict_walk.walk.arg.trylock_only = true;
 	lret = ttm_lru_walk_for_evict(&evict_walk.walk, bdev, man, 1);
-
-	/* One more attempt if we hit low limit? */
 	if (!lret && evict_walk.hit_low) {
 		evict_walk.try_low = true;
 		lret = ttm_lru_walk_for_evict(&evict_walk.walk, bdev, man, 1);
 	}
+
 	if (lret || !ticket)
 		goto out;
 
-	/* Reset low limit */
 	evict_walk.try_low = evict_walk.hit_low = false;
-	/* If ticket-locking, repeat while making progress. */
 	evict_walk.walk.arg.trylock_only = false;
 
 retry:
 	do {
-		/* The walk may clear the evict_walk.walk.ticket field */
 		evict_walk.walk.arg.ticket = ticket;
 		evict_walk.evicted = 0;
 		lret = ttm_lru_walk_for_evict(&evict_walk.walk, bdev, man, 1);
 	} while (!lret && evict_walk.evicted);
 
-	/* We hit the low limit? Try once more */
 	if (!lret && evict_walk.hit_low && !evict_walk.try_low) {
 		evict_walk.try_low = true;
 		goto retry;
@@ -737,7 +767,17 @@ static int ttm_bo_alloc_resource(struct ttm_buffer_object *bo,
 			continue;
 
 		may_evict = (force_space && place->mem_type != TTM_PL_SYSTEM);
-		ret = ttm_resource_alloc(bo, place, res, force_space ? &limit_pool : NULL);
+		{
+			struct dmem_cgroup_pool_state *over_high_pool = NULL;
+
+			ret = ttm_resource_alloc(bo, place, res,
+						 force_space ? &limit_pool : NULL,
+						 &over_high_pool);
+			if (!ret && over_high_pool)
+				ttm_bo_proactive_evict_high(bdev, man, place, bo,
+							    ctx, ticket, over_high_pool);
+			dmem_cgroup_pool_state_put(over_high_pool);
+		}
 		if (ret) {
 			if (ret != -ENOSPC) {
 				dmem_cgroup_pool_state_put(limit_pool);
@@ -1152,7 +1192,7 @@ ttm_bo_swapout_cb(struct ttm_lru_walk *walk, struct ttm_buffer_object *bo)
 
 		memset(&hop, 0, sizeof(hop));
 		place.mem_type = TTM_PL_SYSTEM;
-		ret = ttm_resource_alloc(bo, &place, &evict_mem, NULL);
+		ret = ttm_resource_alloc(bo, &place, &evict_mem, NULL, NULL);
 		if (ret)
 			goto out;
 
diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
index 154d6739256f8..e6ad46d9ff181 100644
--- a/drivers/gpu/drm/ttm/ttm_resource.c
+++ b/drivers/gpu/drm/ttm/ttm_resource.c
@@ -389,7 +389,8 @@ EXPORT_SYMBOL(ttm_resource_fini);
 int ttm_resource_alloc(struct ttm_buffer_object *bo,
 		       const struct ttm_place *place,
 		       struct ttm_resource **res_ptr,
-		       struct dmem_cgroup_pool_state **ret_limit_pool)
+		       struct dmem_cgroup_pool_state **ret_limit_pool,
+		       struct dmem_cgroup_pool_state **ret_over_high_pool)
 {
 	struct ttm_resource_manager *man =
 		ttm_manager_type(bo->bdev, place->mem_type);
@@ -397,7 +398,8 @@ int ttm_resource_alloc(struct ttm_buffer_object *bo,
 	int ret;
 
 	if (man->cg) {
-		ret = dmem_cgroup_try_charge(man->cg, bo->base.size, &pool, ret_limit_pool);
+		ret = dmem_cgroup_try_charge(man->cg, bo->base.size, &pool,
+					     ret_limit_pool, ret_over_high_pool);
 		if (ret) {
 			if (ret == -EAGAIN)
 				ret = -ENOSPC;
@@ -409,6 +411,8 @@ int ttm_resource_alloc(struct ttm_buffer_object *bo,
 	if (ret) {
 		if (pool)
 			dmem_cgroup_uncharge(pool, bo->base.size);
+		if (ret_over_high_pool)
+			dmem_cgroup_pool_state_put(*ret_over_high_pool);
 		return ret;
 	}
 
diff --git a/include/drm/ttm/ttm_resource.h b/include/drm/ttm/ttm_resource.h
index a5d386583fb6e..88fb402acfdc6 100644
--- a/include/drm/ttm/ttm_resource.h
+++ b/include/drm/ttm/ttm_resource.h
@@ -461,7 +461,8 @@ void ttm_resource_fini(struct ttm_resource_manager *man,
 int ttm_resource_alloc(struct ttm_buffer_object *bo,
 		       const struct ttm_place *place,
 		       struct ttm_resource **res,
-		       struct dmem_cgroup_pool_state **ret_limit_pool);
+		       struct dmem_cgroup_pool_state **ret_limit_pool,
+		       struct dmem_cgroup_pool_state **ret_over_high_pool);
 void ttm_resource_free(struct ttm_buffer_object *bo, struct ttm_resource **res);
 bool ttm_resource_intersects(struct ttm_device *bdev,
 			     struct ttm_resource *res,
diff --git a/include/linux/cgroup_dmem.h b/include/linux/cgroup_dmem.h
index dd4869f1d736e..1808bfbbc9a31 100644
--- a/include/linux/cgroup_dmem.h
+++ b/include/linux/cgroup_dmem.h
@@ -19,11 +19,12 @@ struct dmem_cgroup_region *dmem_cgroup_register_region(u64 size, const char *nam
 void dmem_cgroup_unregister_region(struct dmem_cgroup_region *region);
 int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size,
 			   struct dmem_cgroup_pool_state **ret_pool,
-			   struct dmem_cgroup_pool_state **ret_limit_pool);
+			   struct dmem_cgroup_pool_state **ret_limit_pool,
+			   struct dmem_cgroup_pool_state **ret_over_high_pool);
 void dmem_cgroup_uncharge(struct dmem_cgroup_pool_state *pool, u64 size);
 bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
 				      struct dmem_cgroup_pool_state *test_pool,
-				      bool ignore_low, bool *ret_hit_low);
+				      bool try_high, bool ignore_low, bool *ret_hit_low);
 
 void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool);
 #else
@@ -38,13 +39,17 @@ static inline void dmem_cgroup_unregister_region(struct dmem_cgroup_region *regi
 
 static inline int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size,
 					 struct dmem_cgroup_pool_state **ret_pool,
-					 struct dmem_cgroup_pool_state **ret_limit_pool)
+					 struct dmem_cgroup_pool_state **ret_limit_pool,
+					 struct dmem_cgroup_pool_state **ret_over_high_pool)
 {
 	*ret_pool = NULL;
 
 	if (ret_limit_pool)
 		*ret_limit_pool = NULL;
 
+	if (ret_over_high_pool)
+		*ret_over_high_pool = NULL;
+
 	return 0;
 }
 
@@ -54,8 +59,10 @@ static inline void dmem_cgroup_uncharge(struct dmem_cgroup_pool_state *pool, u64
 static inline
 bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
 				      struct dmem_cgroup_pool_state *test_pool,
-				      bool ignore_low, bool *ret_hit_low)
+				      bool try_high, bool ignore_low, bool *ret_hit_low)
 {
+	if (try_high)
+		return false;
 	return true;
 }
 
diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index 4753a67d0f0f2..b322c8a7e2a67 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -156,6 +156,12 @@ set_resource_low(struct dmem_cgroup_pool_state *pool, u64 val)
 	page_counter_set_low(&pool->cnt, val);
 }
 
+static void
+set_resource_high(struct dmem_cgroup_pool_state *pool, u64 val)
+{
+	page_counter_set_high(&pool->cnt, val);
+}
+
 static void
 set_resource_max(struct dmem_cgroup_pool_state *pool, u64 val)
 {
@@ -167,6 +173,11 @@ static u64 get_resource_low(struct dmem_cgroup_pool_state *pool)
 	return pool ? READ_ONCE(pool->cnt.low) : 0;
 }
 
+static u64 get_resource_high(struct dmem_cgroup_pool_state *pool)
+{
+	return pool ? READ_ONCE(pool->cnt.high) : PAGE_COUNTER_MAX;
+}
+
 static u64 get_resource_min(struct dmem_cgroup_pool_state *pool)
 {
 	return pool ? READ_ONCE(pool->cnt.min) : 0;
@@ -186,6 +197,7 @@ static void reset_all_resource_limits(struct dmem_cgroup_pool_state *rpool)
 {
 	set_resource_min(rpool, 0);
 	set_resource_low(rpool, 0);
+	set_resource_high(rpool, PAGE_COUNTER_MAX);
 	set_resource_max(rpool, PAGE_COUNTER_MAX);
 }
 
@@ -289,10 +301,13 @@ dmem_cgroup_calculate_protection(struct dmem_cgroup_pool_state *limit_pool,
  * dmem_cgroup_state_evict_valuable() - Check if we should evict from test_pool
  * @limit_pool: The pool for which we hit limits
  * @test_pool: The pool for which to test
+ * @try_high: Only evict BOs whose usage exceeds the high limit (first pass)
  * @ignore_low: Whether we have to respect low watermarks.
  * @ret_hit_low: Pointer to whether it makes sense to consider low watermark.
  *
  * This function returns true if we can evict from @test_pool, false if not.
+ * When @try_high is set, only pools with usage above their high limit are
+ * evictable, enabling prioritized eviction of over-limit cgroups.
  * When returning false and @ignore_low is false, @ret_hit_low may
  * be set to true to indicate this function can be retried with @ignore_low
  * set to true.
@@ -301,15 +316,26 @@ dmem_cgroup_calculate_protection(struct dmem_cgroup_pool_state *limit_pool,
  */
 bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
 				      struct dmem_cgroup_pool_state *test_pool,
-				      bool ignore_low, bool *ret_hit_low)
+				      bool try_high, bool ignore_low, bool *ret_hit_low)
 {
 	struct dmem_cgroup_pool_state *pool = test_pool;
 	struct page_counter *ctest;
 	u64 used, min, low;
 
-	/* Can always evict from current pool, despite limits */
-	if (limit_pool == test_pool)
+	/*
+	 * When the limit-hitting cgroup's own BOs are being considered
+	 * in try_high mode, only evict them if their pool exceeds its
+	 * own dmem.high limit.  For non-try_high mode, maintain the
+	 * existing behavior: always evict from the limit-hitting pool.
+	 */
+	if (limit_pool == test_pool) {
+		if (try_high && test_pool) {
+			ctest = &test_pool->cnt;
+			used = page_counter_read(ctest);
+			return used > READ_ONCE(ctest->high);
+		}
 		return true;
+	}
 
 	if (limit_pool) {
 		if (!parent_dmemcs(limit_pool->cs))
@@ -330,10 +356,38 @@ bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
 	}
 
 	ctest = &test_pool->cnt;
+	used = page_counter_read(ctest);
+
+	if (try_high) {
+		struct page_counter *c;
+
+		/*
+		 * Walk the page_counter parent chain to check whether any
+		 * ancestor cgroup exceeds its dmem.high limit.  This prevents
+		 * child cgroups from evading the penalty when a parent cgroup
+		 * is over its high limit.
+		 */
+		if (used <= READ_ONCE(ctest->high)) {
+			for (c = ctest->parent; c; c = c->parent) {
+				if (page_counter_read(c) > READ_ONCE(c->high))
+					break;
+			}
+			if (!c)
+				return false;
+		}
+
+		/*
+		 * Respect dmem.min protection: do not evict BOs below the
+		 * effective minimum even during the high-priority pass.
+		 */
+		dmem_cgroup_calculate_protection(limit_pool, test_pool);
+		min = READ_ONCE(ctest->emin);
+
+		return used > min;
+	}
 
 	dmem_cgroup_calculate_protection(limit_pool, test_pool);
 
-	used = page_counter_read(ctest);
 	min = READ_ONCE(ctest->emin);
 
 	if (used <= min)
@@ -634,8 +688,9 @@ EXPORT_SYMBOL_GPL(dmem_cgroup_uncharge);
  * dmem_cgroup_try_charge() - Try charging a new allocation to a region.
  * @region: dmem region to charge
  * @size: Size (in bytes) to charge.
- * @ret_pool: On succesfull allocation, the pool that is charged.
+ * @ret_pool: On successful allocation, the pool that is charged.
  * @ret_limit_pool: On a failed allocation, the limiting pool.
+ * @ret_over_high_pool: On successful allocation, set if usage exceeds dmem.high.
  *
  * This function charges the @region region for a size of @size bytes.
  *
@@ -647,11 +702,17 @@ EXPORT_SYMBOL_GPL(dmem_cgroup_uncharge);
  * eviction as argument to dmem_cgroup_evict_valuable(). This reference must be freed
  * with @dmem_cgroup_pool_state_put().
  *
+ * When the function succeeds and @ret_over_high_pool is non-null, it will be
+ * set if the charged pool's usage now exceeds its dmem.high soft limit. The
+ * caller should trigger proactive eviction to bring usage back under the limit.
+ * This reference must be freed with @dmem_cgroup_pool_state_put().
+ *
  * Return: 0 on success, -EAGAIN on hitting a limit, or a negative errno on failure.
  */
 int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size,
 			  struct dmem_cgroup_pool_state **ret_pool,
-			  struct dmem_cgroup_pool_state **ret_limit_pool)
+			  struct dmem_cgroup_pool_state **ret_limit_pool,
+			  struct dmem_cgroup_pool_state **ret_over_high_pool)
 {
 	struct dmemcg_state *cg;
 	struct dmem_cgroup_pool_state *pool;
@@ -661,6 +722,8 @@ int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size,
 	*ret_pool = NULL;
 	if (ret_limit_pool)
 		*ret_limit_pool = NULL;
+	if (ret_over_high_pool)
+		*ret_over_high_pool = NULL;
 
 	/*
 	 * hold on to css, as cgroup can be removed but resource
@@ -685,6 +748,18 @@ int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size,
 		goto err;
 	}
 
+	/*
+	 * Charge succeeded. Check if usage now exceeds the soft high limit so
+	 * the caller can trigger proactive reclaim to bring the cgroup back
+	 * under its dmem.high threshold.
+	 */
+	if (ret_over_high_pool &&
+	    page_counter_read(&pool->cnt) > READ_ONCE(pool->cnt.high)) {
+		*ret_over_high_pool = pool;
+		css_get(&pool->cs->css);
+		dmemcg_pool_get(*ret_over_high_pool);
+	}
+
 	/* On success, reference from get_current_dmemcs is transferred to *ret_pool */
 	*ret_pool = pool;
 	return 0;
@@ -835,6 +910,17 @@ static ssize_t dmem_cgroup_region_low_write(struct kernfs_open_file *of,
 	return dmemcg_limit_write(of, buf, nbytes, off, set_resource_low);
 }
 
+static int dmem_cgroup_region_high_show(struct seq_file *sf, void *v)
+{
+	return dmemcg_limit_show(sf, v, get_resource_high);
+}
+
+static ssize_t dmem_cgroup_region_high_write(struct kernfs_open_file *of,
+					  char *buf, size_t nbytes, loff_t off)
+{
+	return dmemcg_limit_write(of, buf, nbytes, off, set_resource_high);
+}
+
 static int dmem_cgroup_region_max_show(struct seq_file *sf, void *v)
 {
 	return dmemcg_limit_show(sf, v, get_resource_max);
@@ -868,6 +954,12 @@ static struct cftype files[] = {
 		.seq_show = dmem_cgroup_region_low_show,
 		.flags = CFTYPE_NOT_ON_ROOT,
 	},
+	{
+		.name = "high",
+		.write = dmem_cgroup_region_high_write,
+		.seq_show = dmem_cgroup_region_high_show,
+		.flags = CFTYPE_NOT_ON_ROOT,
+	},
 	{
 		.name = "max",
 		.write = dmem_cgroup_region_max_write,

---
base-commit: ab5fce87a778cb780a05984a2ca448f2b41aafbf
change-id: 20260519-feature-dmem-high-16997148dc38

Best regards,
-- 
Jing Wu <realwujing@gmail.com>



^ permalink raw reply related	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-07-09  9:47 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-07-09  4:02 [PATCH v7] cgroup/dmem: implement dmem.high soft limit with proactive reclaim Qiliang Yuan
2026-07-09  5:44 ` Matthew Brost
2026-07-09  6:11   ` Jing Wu
2026-07-09  9:47     ` Thomas Hellström

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