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memcg-group-the-read-mostly-fields-of-struct-mem_cgroup.patch removed from -mm tree

merged mm-stable Andrew Morton 1 participant 1 message Oct 9

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The quilt patch titled
Subject: memcg: group the read-mostly fields of struct mem_cgroup
has been removed from the -mm tree. Its filename was
memcg-group-the-read-mostly-fields-of-struct-mem_cgroup.patch

This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Shakeel Butt <[email protected]>
Subject: memcg: group the read-mostly fields of struct mem_cgroup
Date: Fri, 4 Sep 2026 20:05:21 -0700

These fields are set when the memcg is created and only read after that:

vmstats_percpu read on every stat update
vmstats
zswap_max, zswap_writeback
private_id read on every eviction and refault
kmemcg_id read on every list_lru lookup
oom_group

Put them in one cache line group at the end of the struct, right before nodeinfo[]. nodeinfo[] is read-mostly too but it is a flexible array, so it cannot sit inside a group. The group ends without padding so the two share a line.

This also drops the ____cacheline_aligned_in_smp on vmstats_percpu added by commit c1afbd5de131 ("mm/memcontrol: avoid false sharing between vmstats and events"). That only aligned the start of the field. cgwb_domain followed it on the same line and is written on every writeout completion. A group boundary covers both sides.

No functional change.

Link https://lore.kernel.org/[email protected] open here
Signed-off-by Shakeel Butt <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Cc Johannes Weiner <[email protected]>
Cc Michal Hocko <[email protected]>
Cc Muchun Song <[email protected]>
Cc Roman Gushchin <[email protected]>

---

 include/linux/memcontrol.h |   62 +++++++++++++++++++----------------
 mm/memcontrol.c            |   17 +++++++++
 2 files changed, 52 insertions(+), 27 deletions(-)
include/linux/memcontrol.h renamed from include/linux/memcontrol.h~memcg-group-the-read-mostly-fields-of-struct-mem_cgroup +35 -27
@@ -183,9 +183,6 @@ struct obj_cgroup {
 struct mem_cgroup {
 	struct cgroup_subsys_state css;
 
-	/* Private memcg ID. Used to ID objects that outlive the cgroup */
-	int private_id;
-
 	/* Accounted resources */
 	struct page_counter memory;		/* Both v1 & v2 */
 

@@ -259,30 +256,6 @@ struct mem_cgroup {
 #endif
 	__cacheline_group_end_aligned(memcg_cold);
 
-#ifdef CONFIG_ZSWAP
-	unsigned long zswap_max;
-
-	/*
-	 * Prevent pages from this memcg from being written back from zswap to
-	 * swap, and from being swapped out on zswap store failures.
-	 */
-	bool zswap_writeback;
-#endif
-
-	/*
-	 * Should the OOM killer kill all belonging tasks, had it kill one?
-	 */
-	bool oom_group;
-
-	/* memory.stat */
-	struct memcg_vmstats	*vmstats;
-
-	int kmemcg_id;
-
-	/* Keep the hot per-CPU stats pointer away from memory event counters. */
-	struct memcg_vmstats_percpu __percpu *vmstats_percpu
-		____cacheline_aligned_in_smp;
-
 #ifdef CONFIG_MEMCG_V1
 	/* v1 only. Not grouped: v1 is legacy, sorting it is not worth it. */
 

@@ -322,6 +295,41 @@ struct mem_cgroup {
 	int swappiness;
 #endif /* CONFIG_MEMCG_V1 */
 
+	/*
+	 * Set when the memcg is created and cleared when it is offlined.
+	 * Never written on a hot path.
+	 */
+	__cacheline_group_begin_aligned(memcg_read_mostly);
+	/* Read on every stat update */
+	struct memcg_vmstats_percpu __percpu *vmstats_percpu;
+
+	/* memory.stat */
+	struct memcg_vmstats	*vmstats;
+
+#ifdef CONFIG_ZSWAP
+	unsigned long zswap_max;
+#endif
+
+	/* Private memcg ID. Used to ID objects that outlive the cgroup */
+	int private_id;
+
+	int kmemcg_id;
+
+	/*
+	 * Should the OOM killer kill all belonging tasks, had it kill one?
+	 */
+	bool oom_group;
+
+#ifdef CONFIG_ZSWAP
+	/*
+	 * Prevent pages from this memcg from being written back from zswap to
+	 * swap, and from being swapped out on zswap store failures.
+	 */
+	bool zswap_writeback;
+#endif
+	/* Not padded: nodeinfo[] is read-mostly too, let it share the line. */
+	__cacheline_group_end(memcg_read_mostly);
+
 	struct mem_cgroup_per_node *nodeinfo[];
 };
mm/memcontrol.c renamed from mm/memcontrol.c~memcg-group-the-read-mostly-fields-of-struct-mem_cgroup +17 -0
@@ -5753,6 +5753,23 @@ static void __init memcg_struct_check(vo
 	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_cold,
 				      mm_list);
 #endif
+
+	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_read_mostly,
+				      vmstats_percpu);
+	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_read_mostly,
+				      vmstats);
+#ifdef CONFIG_ZSWAP
+	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_read_mostly,
+				      zswap_max);
+	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_read_mostly,
+				      zswap_writeback);
+#endif
+	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_read_mostly,
+				      private_id);
+	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_read_mostly,
+				      kmemcg_id);
+	CACHELINE_ASSERT_GROUP_MEMBER(struct mem_cgroup, memcg_read_mostly,
+				      oom_group);
 }
 
 int __init mem_cgroup_init(void)

_

Patches currently in -mm which might be from [email protected] are