Re: [linux-next:master] [mm/vmpressure] ea928e9e18: stress-ng.mremap.ops_per_sec 36.2% regression

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Aug 13, 2026 at 09:16:22PM +0800, kernel test robot wrote:
> 
> 
> Hello,
> 
> kernel test robot noticed a 36.2% regression of stress-ng.mremap.ops_per_sec on:
> 
> commit: ea928e9e18da682e9a5bc40aa862bff7ce5ae42e ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c") https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
> 
> in testcase: stress-ng
> version: stress-ng-x86_64-29ce10a2c-1_20260712
> with following parameters:
> 
> 	nr_threads: 100%
> 	testtime: 60s
> 	test: mremap
> 	cpufreq_governor: performance
> 
> 
> 
> config: x86_64-rhel-9.4 (CONFIG_MEMCG=y and CONFIG_MEMCG_V1 is not set)
> compiler: gcc-14
> test machine: 256 threads 4 sockets INTEL(R) XEON(R) PLATINUM 8592+ (Emerald Rapids) with 256G memory
> 
> (please refer to attached dmesg/kmsg for entire log/backtrace)
> 

Hi there,

Can you please test the following patch and see if it fixes the regression?


From 84c0b05b3bc5cf73ee66ead75aafb1ad684462c3 Mon Sep 17 00:00:00 2001
From: Shakeel Butt <shakeel.butt@linux.dev>
Date: Thu, 13 Aug 2026 09:38:28 -0700
Subject: [PATCH] memcg: keep vmstats_percpu off the memory_events[] cacheline

Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
---
 include/linux/memcontrol.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e78bc98ab229..e25d5b9a1db8 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -246,8 +246,13 @@ struct mem_cgroup {
 	/* handle for "memory.swap.events" */
 	struct cgroup_file swap_events_file;
 
-	/* memory.stat */
+	/* Read-mostly. */
 	struct memcg_vmstats	*vmstats;
+	struct memcg_vmstats_percpu __percpu *vmstats_percpu;
+	int			kmemcg_id;
+
+	/* Write-hot from here on; do not let it share with the above. */
+	CACHELINE_PADDING(_pad_);
 
 	/* memory.events */
 	atomic_long_t		memory_events[MEMCG_NR_MEMORY_EVENTS];
@@ -266,9 +271,6 @@ struct mem_cgroup {
 #if BITS_PER_LONG < 64
 	seqlock_t		socket_pressure_seqlock;
 #endif
-	int kmemcg_id;
-
-	struct memcg_vmstats_percpu __percpu *vmstats_percpu;
 
 #ifdef CONFIG_CGROUP_WRITEBACK
 	struct list_head cgwb_list;
-- 
2.53.0-Meta