+ mm-memcontrol-avoid-false-sharing-between-vmstats-and-events.patch added to mm-unstable branch

The patch titled
     Subject: mm/memcontrol: avoid false sharing between vmstats and events
has been added to the -mm mm-unstable branch.  Its filename is
     mm-memcontrol-avoid-false-sharing-between-vmstats-and-events.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcontrol-avoid-false-sharing-between-vmstats-and-events.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Usama Arif <[email protected]>
Subject: mm/memcontrol: avoid false sharing between vmstats and events
Date: Mon, 17 Aug 2026 03:38:35 -0700

Moving v1 userspace eventfd handling into memcontrol-v1.c shrank struct
vmpressure from 112 to 24 bytes when CONFIG_MEMCG_V1 is disabled.  This
moved memory_events_local[MEMCG_SWAP_FAIL] and the hot vmstats_percpu
pointer onto the same cacheline.

The stress-ng mremap stressor exercises MADV_PAGEOUT with swap disabled,
generating about 20 million MEMCG_SWAP_FAIL updates per 60-second run on a
176-CPU test system.  Those writes bounce the line while memcg statistics
paths load vmstats_percpu.

Move cgwb_list into the existing alignment gap and cacheline-align
vmstats_percpu.  This separates the pointer from the event counters
without increasing the size of struct mem_cgroup in the tested
configuration.

The blamed commit reduced median mremap throughput by 4.38% on the test
system with one socket.  The patched kernel brings the performance to
within 0.5% of the parent which is within the observed boot-to-boot spread
(up to 1.2%).

Link: https://lore.kernel.org/[email protected]
Fixes: ea928e9e18da ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c")
Signed-off-by: Usama Arif <[email protected]>
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-lkp/[email protected]
Acked-by: Shakeel Butt <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Yi Lai <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 include/linux/memcontrol.h |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/include/linux/memcontrol.h~mm-memcontrol-avoid-false-sharing-between-vmstats-and-events
+++ a/include/linux/memcontrol.h
@@ -268,10 +268,15 @@ struct mem_cgroup {
 #endif
 	int kmemcg_id;
 
-	struct memcg_vmstats_percpu __percpu *vmstats_percpu;
-
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct list_head cgwb_list;
+#endif
+
+	/* 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_CGROUP_WRITEBACK
 	struct wb_domain cgwb_domain;
 	struct memcg_cgwb_frn cgwb_frn[MEMCG_CGWB_FRN_CNT];
 #endif
_

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

mm-vmstat-mm-memcontrol-add-_monotonic-vmstat-readers.patch
mm-vmscan-add-pgrotate_anon-and-pgrotate_file-vmstat-counters.patch
mm-vmscan-reduce-lru_lock-contention-via-vmstat-derived-scan-balance-cost.patch
mm-memcontrol-avoid-false-sharing-between-vmstats-and-events.patch
squashfs-avoid-thundering-herd-cache-wakeups.patch