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h=Date:From:To:Cc:Subject:In-Reply-To:References; b=eKkxo1KRikpizP51WbuqCMzjbpsMC2EB66RDsQvKs8ZF6hUQ2yzOxhKRJwpwRk0RM SvRpNBy0qrEWJRYHQvfYbb1gFQvJzRVbAKrWOX+MYnlTSghqalzzxK+zA3VajtvzZO mx/iPyqBLKgzIfRv2Gax1+Ob7z8N7wH2yITp70mc= Date: Mon, 17 Aug 2026 10:43:40 -0700 From: Andrew Morton To: Usama Arif 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 Subject: Re: [PATCH] mm/memcontrol: avoid false sharing between vmstats and events Message-Id: <20260817104340.c9bd2dae70d4fa31fd66b216@linux-foundation.org> In-Reply-To: <20260817103835.2937733-1-usama.arif@linux.dev> References: <20260817103835.2937733-1-usama.arif@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8ACA340007 X-Stat-Signature: ox1etz89qrtcc3abkzhpwincatdx1mod X-HE-Tag: 1786988622-769794 X-HE-Meta: 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 amI/PVgo dZPoxdM0sLMQpQNorcRjeLvDaeqMqWU99sBuCxExEn9VcDs6P5gTaLf8W/ru0uTM5DAkowoCVogC4piqhRDI8nMysNthsw34ENdC2kBdBzzXQDmqdUUe1ehBqoP+s+SqmP1L44YVLKXwEZ4rGoaBZRvBOc2XbnTQR65TIPc0XI068r804HT0Pn8E9QbALFm+ZcjmpZMknVFlxcC8BCN2UzJZ4WCqhph7UWNII6wBAaSSwQuX9gTJii80dMBHVVydJBvMw Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 17 Aug 2026 03:38:35 -0700 Usama Arif 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.