[merged mm-stable] mm-memcontrol-avoid-false-sharing-between-vmstats-and-events.patch removed from -mm tree

[merged mm-stable] mm-memcontrol-avoid-false-sharing-between-vmstats-and-events.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: mm/memcontrol: avoid false sharing between vmstats and events
has been removed from the -mm tree.  Its filename was
     mm-memcontrol-avoid-false-sharing-between-vmstats-and-events.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: Usama Arif <usama.arif@linux.dev>
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/20260817103835.2937733-1-usama.arif@linux.dev
Fixes: ea928e9e18da ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c")
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Reported-by: kernel test robot <yi1.lai@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202608131743.c6a7dda4-lkp@intel.com
Tested-by: kernel test robot <yi1.lai@intel.com>
  Link: http://lore.kernel.org/aoAABX59IzUXz/Rv@ly-workstation
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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 usama.arif@linux.dev are

mm-huge_memory-transfer-the-pmd-dirty-bit-to-the-folio-on-zap.patch