From: Andrew Morton <akpm@linux-foundation.org>
To: Usama Arif <usama.arif@linux.dev>
Cc: shakeel.butt@linux.dev, cgroups@vger.kernel.org,
hannes@cmpxchg.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, mhocko@kernel.org, muchun.song@linux.dev,
roman.gushchin@linux.dev, david@kernel.org, kernel-team@meta.com,
kernel test robot <yi1.lai@intel.com>
Subject: Re: [PATCH] mm/memcontrol: avoid false sharing between vmstats and events
Date: Mon, 17 Aug 2026 10:43:40 -0700 [thread overview]
Message-ID: <20260817104340.c9bd2dae70d4fa31fd66b216@linux-foundation.org> (raw)
In-Reply-To: <20260817103835.2937733-1-usama.arif@linux.dev>
On Mon, 17 Aug 2026 03:38:35 -0700 Usama Arif <usama.arif@linux.dev> wrote:
> 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%).
Cool, thanks.
> Fixes: ea928e9e18da ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c")
That's in mm-stable so I'll squeeze this fix into next week's 7.3-rc1
merge pile.
next prev parent reply other threads:[~2026-08-17 17:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-17 10:38 [PATCH] mm/memcontrol: avoid false sharing between vmstats and events Usama Arif
2026-08-17 17:43 ` Andrew Morton [this message]
2026-08-17 17:54 ` Shakeel Butt
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