[PATCH 2/3] mm: page_counter: track protection state in page_counter_protection

From: linuszeng <hidden>
Date: 2026-09-09 08:08:53
Also in: cgroups, dri-devel, linux-mm, lkml
Subsystem: control group (cgroup), control group - device memory controller (dmem), control group - memory resource controller (memcg), memory management, the rest · Maintainers: Tejun Heo, Johannes Weiner, Michal Koutný, Maarten Lankhorst, Maxime Ripard, Natalie Vock, Michal Hocko, Roman Gushchin, Shakeel Butt, Andrew Morton, Linus Torvalds

Move the read/write side of hierarchical protection from struct
page_counter to struct page_counter_protection: propagate_protected_usage()
updates the protection context of the parent, page_counter_set_min()/low()
and page_counter_calculate_protection() operate on it, and memcg and dmem
accessors (including dmem_cgroup_below_min()/below_low()) read
min/low/emin/elow and children_*_usage from it.

struct page_counter keeps its now-unused protection fields for now; they
are removed in a follow-up commit.

No functional change.
---
 include/linux/memcontrol.h |  8 +++----
 kernel/cgroup/dmem.c       | 12 +++++-----
 mm/memcontrol.c            |  8 +++----
 mm/page_counter.c          | 59 +++++++++++++++++++++++++++++-----------------
 4 files changed, 52 insertions(+), 35 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index ed863f4ed233..44065001a66a 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h

@@ -591,8 +591,8 @@ static inline void mem_cgroup_protection(struct mem_cgroup *root,
 	if (root == memcg)
 		return;
 
-	*min = READ_ONCE(memcg->memory.emin);
-	*low = READ_ONCE(memcg->memory.elow);
+	*min = READ_ONCE(memcg->memory_prot.emin);
+	*low = READ_ONCE(memcg->memory_prot.elow);
 }
 
 void mem_cgroup_calculate_protection(struct mem_cgroup *root,

@@ -616,7 +616,7 @@ static inline bool mem_cgroup_below_low(struct mem_cgroup *target,
 	if (mem_cgroup_unprotected(target, memcg))
 		return false;
 
-	return READ_ONCE(memcg->memory.elow) >=
+	return READ_ONCE(memcg->memory_prot.elow) >=
 		page_counter_read(&memcg->memory);
 }

@@ -626,7 +626,7 @@ static inline bool mem_cgroup_below_min(struct mem_cgroup *target,
 	if (mem_cgroup_unprotected(target, memcg))
 		return false;
 
-	return READ_ONCE(memcg->memory.emin) >=
+	return READ_ONCE(memcg->memory_prot.emin) >=
 		page_counter_read(&memcg->memory);
 }

diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index e33d807cdea8..10321f1f0330 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c

@@ -212,12 +212,12 @@ set_resource_max(struct dmem_cgroup_pool_state *pool, u64 val, bool nonblock)
 
 static u64 get_resource_low(struct dmem_cgroup_pool_state *pool)
 {
-	return pool ? READ_ONCE(pool->cnt.low) : 0;
+	return pool ? READ_ONCE(pool->cnt.prot->low) : 0;
 }
 
 static u64 get_resource_min(struct dmem_cgroup_pool_state *pool)
 {
-	return pool ? READ_ONCE(pool->cnt.min) : 0;
+	return pool ? READ_ONCE(pool->cnt.prot->min) : 0;
 }
 
 static u64 get_resource_max(struct dmem_cgroup_pool_state *pool)

@@ -388,13 +388,13 @@ bool dmem_cgroup_state_evict_valuable(struct dmem_cgroup_pool_state *limit_pool,
 	dmem_cgroup_calculate_protection(limit_pool, test_pool);
 
 	used = page_counter_read(ctest);
-	min = READ_ONCE(ctest->emin);
+	min = READ_ONCE(ctest->prot->emin);
 
 	if (used <= min)
 		return false;
 
 	if (!ignore_low) {
-		low = READ_ONCE(ctest->elow);
+		low = READ_ONCE(ctest->prot->elow);
 		if (used > low)
 			return true;

@@ -786,7 +786,7 @@ bool dmem_cgroup_below_min(struct dmem_cgroup_pool_state *root,
 	 * here.
 	 */
 	dmem_cgroup_calculate_protection(root, test);
-	return page_counter_read(&test->cnt) <= READ_ONCE(test->cnt.emin);
+	return page_counter_read(&test->cnt) <= READ_ONCE(test->cnt.prot->emin);
 }
 EXPORT_SYMBOL_GPL(dmem_cgroup_below_min);

@@ -817,7 +817,7 @@ bool dmem_cgroup_below_low(struct dmem_cgroup_pool_state *root,
 	 * here.
 	 */
 	dmem_cgroup_calculate_protection(root, test);
-	return page_counter_read(&test->cnt) <= READ_ONCE(test->cnt.elow);
+	return page_counter_read(&test->cnt) <= READ_ONCE(test->cnt.prot->elow);
 }
 EXPORT_SYMBOL_GPL(dmem_cgroup_below_low);

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ffa1ced3baae..b4c01a0dfd4f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c

@@ -4823,7 +4823,7 @@ static ssize_t memory_peak_write(struct kernfs_open_file *of, char *buf,
 static int memory_min_show(struct seq_file *m, void *v)
 {
 	return seq_puts_memcg_tunable(m,
-		READ_ONCE(mem_cgroup_from_seq(m)->memory.min));
+		READ_ONCE(mem_cgroup_from_seq(m)->memory_prot.min));
 }
 
 static ssize_t memory_min_write(struct kernfs_open_file *of,

@@ -4846,7 +4846,7 @@ static ssize_t memory_min_write(struct kernfs_open_file *of,
 static int memory_low_show(struct seq_file *m, void *v)
 {
 	return seq_puts_memcg_tunable(m,
-		READ_ONCE(mem_cgroup_from_seq(m)->memory.low));
+		READ_ONCE(mem_cgroup_from_seq(m)->memory_prot.low));
 }
 
 static ssize_t memory_low_write(struct kernfs_open_file *of,

@@ -6271,6 +6271,6 @@ void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg)
 		memcg = root_mem_cgroup;
 
 	pr_warn("Memory cgroup min protection %lukB -- low protection %lukB",
-		K(atomic_long_read(&memcg->memory.children_min_usage)),
-		K(atomic_long_read(&memcg->memory.children_low_usage)));
+		K(atomic_long_read(&memcg->memory_prot.children_min_usage)),
+		K(atomic_long_read(&memcg->memory_prot.children_low_usage)));
 }

diff --git a/mm/page_counter.c b/mm/page_counter.c
index 38cb99f5f50e..401201c8e390 100644
--- a/mm/page_counter.c
+++ b/mm/page_counter.c

@@ -21,28 +21,29 @@ static bool track_protection(struct page_counter *c)
 static void propagate_protected_usage(struct page_counter *c,
 				      unsigned long usage)
 {
+	struct page_counter_protection *prot = c->prot;
 	unsigned long protected, old_protected;
 	long delta;
 
-	if (!c->parent)
+	if (!prot || !prot->parent)
 		return;
 
-	protected = min(usage, READ_ONCE(c->min));
-	old_protected = atomic_long_read(&c->min_usage);
+	protected = min(usage, READ_ONCE(prot->min));
+	old_protected = atomic_long_read(&prot->min_usage);
 	if (protected != old_protected) {
-		old_protected = atomic_long_xchg(&c->min_usage, protected);
+		old_protected = atomic_long_xchg(&prot->min_usage, protected);
 		delta = protected - old_protected;
 		if (delta)
-			atomic_long_add(delta, &c->parent->children_min_usage);
+			atomic_long_add(delta, &prot->parent->children_min_usage);
 	}
 
-	protected = min(usage, READ_ONCE(c->low));
-	old_protected = atomic_long_read(&c->low_usage);
+	protected = min(usage, READ_ONCE(prot->low));
+	old_protected = atomic_long_read(&prot->low_usage);
 	if (protected != old_protected) {
-		old_protected = atomic_long_xchg(&c->low_usage, protected);
+		old_protected = atomic_long_xchg(&prot->low_usage, protected);
 		delta = protected - old_protected;
 		if (delta)
-			atomic_long_add(delta, &c->parent->children_low_usage);
+			atomic_long_add(delta, &prot->parent->children_low_usage);
 	}
 }

@@ -257,7 +258,10 @@ void page_counter_set_min(struct page_counter *counter, unsigned long nr_pages)
 {
 	struct page_counter *c;
 
-	WRITE_ONCE(counter->min, nr_pages);
+	if (!counter->prot)
+		return;
+
+	WRITE_ONCE(counter->prot->min, nr_pages);
 
 	for (c = counter; c; c = c->parent)
 		propagate_protected_usage(c, atomic_long_read(&c->usage));

@@ -274,7 +278,10 @@ void page_counter_set_low(struct page_counter *counter, unsigned long nr_pages)
 {
 	struct page_counter *c;
 
-	WRITE_ONCE(counter->low, nr_pages);
+	if (!counter->prot)
+		return;
+
+	WRITE_ONCE(counter->prot->low, nr_pages);
 
 	for (c = counter; c; c = c->parent)
 		propagate_protected_usage(c, atomic_long_read(&c->usage));

@@ -445,9 +452,18 @@ void page_counter_calculate_protection(struct page_counter *root,
 				       struct page_counter *counter,
 				       bool recursive_protection)
 {
+	struct page_counter_protection *prot = counter->prot;
+	struct page_counter_protection *parent_prot;
 	unsigned long usage, parent_usage;
 	struct page_counter *parent = counter->parent;
 
+	/*
+	 * Only counters with protection support (memory, dmem pools) are
+	 * ever passed here, but guard anyway.
+	 */
+	if (!prot)
+		return;
+
 	/*
 	 * Effective values of the reclaim targets are ignored so they
 	 * can be stale. Have a look at mem_cgroup_protection for more

@@ -463,23 +479,24 @@ void page_counter_calculate_protection(struct page_counter *root,
 		return;
 
 	if (parent == root) {
-		counter->emin = READ_ONCE(counter->min);
-		counter->elow = READ_ONCE(counter->low);
+		prot->emin = READ_ONCE(prot->min);
+		prot->elow = READ_ONCE(prot->low);
 		return;
 	}
 
+	parent_prot = parent->prot;
 	parent_usage = page_counter_read(parent);
 
-	WRITE_ONCE(counter->emin, effective_protection(usage, parent_usage,
-			READ_ONCE(counter->min),
-			READ_ONCE(parent->emin),
-			atomic_long_read(&parent->children_min_usage),
+	WRITE_ONCE(prot->emin, effective_protection(usage, parent_usage,
+			READ_ONCE(prot->min),
+			READ_ONCE(parent_prot->emin),
+			atomic_long_read(&parent_prot->children_min_usage),
 			recursive_protection));
 
-	WRITE_ONCE(counter->elow, effective_protection(usage, parent_usage,
-			READ_ONCE(counter->low),
-			READ_ONCE(parent->elow),
-			atomic_long_read(&parent->children_low_usage),
+	WRITE_ONCE(prot->elow, effective_protection(usage, parent_usage,
+			READ_ONCE(prot->low),
+			READ_ONCE(parent_prot->elow),
+			atomic_long_read(&parent_prot->children_low_usage),
 			recursive_protection));
 }
 #endif /* CONFIG_MEMCG || CONFIG_CGROUP_DMEM */

-- 
2.43.7

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