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Wed, 10 Jul 2024 19:22:10 -0700 (PDT) MIME-Version: 1.0 References: <20240707094956.94654-1-laoar.shao@gmail.com> <20240707094956.94654-4-laoar.shao@gmail.com> <878qyaarm6.fsf@yhuang6-desk2.ccr.corp.intel.com> In-Reply-To: <878qyaarm6.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Yafang Shao Date: Thu, 11 Jul 2024 10:21:34 +0800 Message-ID: Subject: Re: [PATCH 3/3] mm/page_alloc: Introduce a new sysctl knob vm.pcp_batch_scale_max To: "Huang, Ying" Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, linux-mm@kvack.org, Matthew Wilcox , David Rientjes Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 84AB71C001B X-Stat-Signature: cb3wgnxjiwaxe36ibq39wq5gf917iki9 X-HE-Tag: 1720664531-91249 X-HE-Meta: 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 Jw6wsq7b 7/uZg+WDW/+P13EUz8JhGN/NpBiR7csB2NPNHdlhV3jv/tLvAH1pS2iPbNpteOLuVKnuY5KOU2rNLt88a1tze2tjnKlkN3nC2pwiXjlRpdSGRa3cvtJ3vnl1AqmM0UKZR3Wo4FZ1cp0tClFyzMoWdaIG0XfYTJuhxPrORjJ5Fe0c4KS71C3jsDCAXrgfcFRsMlN3vc2hyB4QSvy5mmEAzxm83HSm8I+HCg7XyFvNmnpa3G975XOUmTv52hzqunJ7GJIRMuVXFKF6/Wqq2c04BSo45QFermCWCUlrhptlaUzIkYwvfK32tybNCWPMP9ku0QjAjMq1Drg9BU25NmVnDHD0o/H9bqJWmD8WGmIa4ZUthu4chyesGs2Coc5AHDMIP/X5zWuLfX/MnkL3Wb0QgWJrGYTkjFKrFwm5A X-Bogosity: Ham, tests=bogofilter, spamicity=0.000034, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 10, 2024 at 10:51=E2=80=AFAM Huang, Ying = wrote: > > Yafang Shao writes: > > > The configuration parameter PCP_BATCH_SCALE_MAX poses challenges for > > quickly experimenting with specific workloads in a production environme= nt, > > particularly when monitoring latency spikes caused by contention on the > > zone->lock. To address this, a new sysctl parameter vm.pcp_batch_scale_= max > > is introduced as a more practical alternative. > > In general, I'm neutral to the change. I can understand that kernel > configuration isn't as flexible as sysctl knob. But, sysctl knob is ABI > too. > > > To ultimately mitigate the zone->lock contention issue, several suggest= ions > > have been proposed. One approach involves dividing large zones into mul= ti > > smaller zones, as suggested by Matthew[0], while another entails splitt= ing > > the zone->lock using a mechanism similar to memory arenas and shifting = away > > from relying solely on zone_id to identify the range of free lists a > > particular page belongs to[1]. However, implementing these solutions is > > likely to necessitate a more extended development effort. > > Per my understanding, the change will hurt instead of improve zone->lock > contention. Instead, it will reduce page allocation/freeing latency. I'm quite perplexed by your recent comment. You introduced a configuration that has proven to be difficult to use, and you have been resistant to suggestions for modifying it to a more user-friendly and practical tuning approach. May I inquire about the rationale behind introducing this configuration in the beginning? --=20 Regards Yafang