mm: memcg: dump memcg protection info on oom or alloc failures

Currently kernel dumps memory state on oom and allocation failures. One of the question usually raised on those dumps is why the kernel has not reclaimed the reclaimable memory instead of triggering oom. One potential reason is the usage of memory protection provided by memcg. So, let's also dump the memory protected by the memcg in such reports to ease the debugging.

Signed-off-by Shakeel Butt <[email protected]>

---

mm/memcontrol.c +3 -0

index c34029e92bab..623446821b00 100644
@@ -5636,3 +5636,16 @@ bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid)
 {
 	return memcg ? cpuset_node_allowed(memcg->css.cgroup, nid) : true;
 }
+
+void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg)
+{

Quoted 9 lines · On Fri, 7 Nov 2025 15:40:41 -0800 Shakeel Butt <[email protected]> wrote:

Currently kernel dumps memory state on oom and allocation failures. One of the question usually raised on those dumps is why the kernel has not reclaimed the reclaimable memory instead of triggering oom. One potential reason is the usage of memory protection provided by memcg. So, let's also dump the memory protected by the memcg in such reports to ease the debugging.

Signed-off-by Shakeel Butt <[email protected]>

---

[...]

Quoted 11 lines

mm/memcontrol.c +3 -0

index c34029e92bab..623446821b00 100644
@@ -5636,3 +5636,16 @@ bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid)
 {
 	return memcg ? cpuset_node_allowed(memcg->css.cgroup, nid) : true;
 }
+
+void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg)
+{

mm/memcontrol.c bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid) · line 5651

Quoted 10 lines

mm/memcontrol.c +10 -0

+	if (mem_cgroup_disabled() || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return;
+
+	if (!memcg)
+		memcg = root_mem_cgroup;
+
+	pr_warn("Memory cgroup min protection %lukB -- low protection %lukB",
+		K(atomic_long_read(&memcg->memory.children_min_usage)*PAGE_SIZE),
+		K(atomic_long_read(&memcg->memory.children_low_usage)*PAGE_SIZE));
+}

I didn't expect this function is showing the information by calling pr_warn(). To me, "show" feels like something for file operations, like memory_min_show().

What about s/show/dump/ on the name? It makes it more consistent with the subject of this patch, and other similar functions like dump_page() ?

No strong opinion. The current name is also ok for me, but I'm just curious your thought.

Currently kernel dumps memory state on oom and allocation failures. One of the question usually raised on those dumps is why the kernel has not reclaimed the reclaimable memory instead of triggering oom. One potential reason is the usage of memory protection provided by memcg. So, let's also dump the memory protected by the memcg in such reports to ease the debugging.

Signed-off-by Shakeel Butt <[email protected]>

---
 include/linux/memcontrol.h |  5 +++++
 mm/memcontrol.c            | 13 +++++++++++++
 mm/oom_kill.c              |  1 +
 mm/page_alloc.c            |  1 +
 4 files changed, 20 insertions(+)

include/linux/memcontrol.h +5 -0

index 8d2e250535a8..6861f0ff02b5 100644
@@ -1779,6 +1779,7 @@ static inline bool memcg_is_dying(struct mem_cgroup *memcg)
 	return memcg ? css_is_dying(&memcg->css) : false;
 }
 
+void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg);
 #else
 static inline bool mem_cgroup_kmem_disabled(void)
 {

@@ -1850,6 +1851,10 @@ static inline bool memcg_is_dying(struct mem_cgroup *memcg)
 {
 	return false;
 }
+
+static inline void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg)
+{
+}
 #endif /* CONFIG_MEMCG */
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_ZSWAP)

mm/memcontrol.c +13 -0

index c34029e92bab..623446821b00 100644
@@ -5636,3 +5636,16 @@ bool mem_cgroup_node_allowed(struct mem_cgroup *memcg, int nid)
 {
 	return memcg ? cpuset_node_allowed(memcg->css.cgroup, nid) : true;
 }
+
+void mem_cgroup_show_protected_memory(struct mem_cgroup *memcg)
+{
+	if (mem_cgroup_disabled() || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
+		return;
+
+	if (!memcg)
+		memcg = root_mem_cgroup;
+
+	pr_warn("Memory cgroup min protection %lukB -- low protection %lukB",
+		K(atomic_long_read(&memcg->memory.children_min_usage)*PAGE_SIZE),
+		K(atomic_long_read(&memcg->memory.children_low_usage)*PAGE_SIZE));
+}

mm/oom_kill.c +1 -0

index c145b0feecc1..5eb11fbba704 100644
@@ -472,6 +472,7 @@ static void dump_header(struct oom_control *oc)
 		if (should_dump_unreclaim_slab())
 			dump_unreclaimable_slab();
 	}
+	mem_cgroup_show_protected_memory(oc->memcg);
 	if (sysctl_oom_dump_tasks)
 		dump_tasks(oc);
 }

mm/page_alloc.c +1 -0

index e4efda1158b2..26be5734253f 100644
@@ -3977,6 +3977,7 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
 		filter &= ~SHOW_MEM_FILTER_NODES;
 
 	__show_mem(filter, nodemask, gfp_zone(gfp_mask));
+	mem_cgroup_show_protected_memory(NULL);
 }
 
 void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)

Signature · 1 line

2.47.3

Currently kernel dumps memory state on oom and allocation failures. One of the question usually raised on those dumps is why the kernel has not reclaimed the reclaimable memory instead of triggering oom. One potential reason is the usage of memory protection provided by memcg. So, let's also dump the memory protected by the memcg in such reports to ease the debugging.

Signed-off-by Shakeel Butt <[email protected]>