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[109.81.86.48]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482a5b81748sm9986909f8f.37.2026.08.18.00.42.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2026 00:42:15 -0700 (PDT) Date: Tue, 18 Aug 2026 09:42:14 +0200 From: Michal Hocko To: Usama Arif Cc: shakeel.butt@linux.dev, cgroups@vger.kernel.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, muchun.song@linux.dev, roman.gushchin@linux.dev, Andrew Morton , david@kernel.org, kernel-team@meta.com, kernel test robot Subject: Re: [PATCH] mm/memcontrol: avoid false sharing between vmstats and events Message-ID: References: <20260817103835.2937733-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260817103835.2937733-1-usama.arif@linux.dev> On Mon 17-08-26 03:38:35, 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%). > > Fixes: ea928e9e18da ("mm/vmpressure: move v1 userspace eventfd code into memcontrol-v1.c") > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-lkp/202608131743.c6a7dda4-lkp@intel.com > Signed-off-by: Usama Arif > Acked-by: Shakeel Butt Acked-by: Michal Hocko Thanks! > --- > include/linux/memcontrol.h | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index e78bc98ab229b..215e2e87f42b2 100644 > --- a/include/linux/memcontrol.h > +++ b/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 > -- > 2.53.0-Meta -- Michal Hocko SUSE Labs