[PATCH v3 1/5] cgroup/dmem: Add queries for protection values

Natalie Vock
2025-11-10T12:39:30Z

Callers can use this feedback to be more aggressive in making space for
allocations of a cgroup if they know it is protected.

These are counterparts to memcg's mem_cgroup_below_{min,low}.

Signed-off-by: Natalie Vock <natalie.vock@gmx.de>
---
include/linux/cgroup_dmem.h | 16 ++++++++++++
kernel/cgroup/dmem.c | 62 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 78 insertions(+)

diff --git a/include/linux/cgroup_dmem.h b/include/linux/cgroup_dmem.h
index dd4869f1d736e..1a88cd0c9eb00 100644
--- a/include/linux/cgroup_dmem.h
+++ b/include/linux/cgroup_dmem.h
@@ -24,6 +24,10 @@ 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 dmem_cgroup_below_min(struct dmem_cgroup_pool_state *root,
+ struct dmem_cgroup_pool_state *test);
+bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root,
+ struct dmem_cgroup_pool_state *test);

void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool);
#else
@@ -59,6 +63,18 @@ bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
return true;
}

+static inline bool dmem_cgroup_below_min(struct dmem_cgroup_pool_state *root,
+ struct dmem_cgroup_pool_state *test)
+{
+ return false;
+}
+
+static inline bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root,
+ struct dmem_cgroup_pool_state *test)
+{
+ return false;
+}
+
static inline void dmem_cgroup_pool_state_put(struct dmem_cgroup_pool_state *pool)
{ }

diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index 10b63433f0573..314c37c06f81e 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -641,6 +641,68 @@ int dmem_cgroup_try_charge(struct dmem_cgroup_region *region, u64 size,
}
EXPORT_SYMBOL_GPL(dmem_cgroup_try_charge);

+/**
+ * dmem_cgroup_below_min() - Tests whether current usage is within min limit.
+ *
+ * @root: Root of the subtree to calculate protection for, or NULL to calculate global protection.
+ * @test: The pool to test the usage/min limit of.
+ *
+ * Return: true if usage is below min and the cgroup is protected, false otherwise.
+ */
+bool dmem_cgroup_below_min(struct dmem_cgroup_pool_state *root,
+ struct dmem_cgroup_pool_state *test)
+{
+ if (root == test || !pool_parent(test))
+ return false;
+
+ if (!root) {
+ for (root = test; pool_parent(root); root = pool_parent(root))
+ {}
+ }
+
+ /*
+ * In mem_cgroup_below_min(), the memcg pendant, this call is missing.
+ * mem_cgroup_below_min() gets called during traversal of the cgroup tree, where
+ * protection is already calculated as part of the traversal. dmem cgroup eviction
+ * does not traverse the cgroup tree, so we need to recalculate effective protection
+ * here.
+ */
+ dmem_cgroup_calculate_protection(root, test);
+ return page_counter_read(&test->cnt) <= READ_ONCE(test->cnt.emin);
+}
+EXPORT_SYMBOL_GPL(dmem_cgroup_below_min);
+
+/**
+ * dmem_cgroup_below_low() - Tests whether current usage is within low limit.
+ *
+ * @root: Root of the subtree to calculate protection for, or NULL to calculate global protection.
+ * @test: The pool to test the usage/low limit of.
+ *
+ * Return: true if usage is below low and the cgroup is protected, false otherwise.
+ */
+bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root,
+ struct dmem_cgroup_pool_state *test)
+{
+ if (root == test || !pool_parent(test))
+ return false;
+
+ if (!root) {
+ for (root = test; pool_parent(root); root = pool_parent(root))
+ {}
+ }
+
+ /*
+ * In mem_cgroup_below_low(), the memcg pendant, this call is missing.
+ * mem_cgroup_below_low() gets called during traversal of the cgroup tree, where
+ * protection is already calculated as part of the traversal. dmem cgroup eviction
+ * does not traverse the cgroup tree, so we need to recalculate effective protection
+ * here.
+ */
+ dmem_cgroup_calculate_protection(root, test);
+ return page_counter_read(&test->cnt) <= READ_ONCE(test->cnt.elow);
+}
+EXPORT_SYMBOL_GPL(dmem_cgroup_below_low);
+
static int dmem_cgroup_region_capacity_show(struct seq_file *sf, void *v)
{
struct dmem_cgroup_region *region;

--
2.51.2