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bh=tJ16Bk0WI8y8XcmDkzMO+dBcBAplNjNR2GBLgl4eFgQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=nG9gJJjNM1REQ9Dp2YlErXGNujtva4AwRxgbaw//vEAA+mb9a2qG+/9ZCpzJdNayg rrjBRTylp+09XRSUZBbv3eM65UQCWET0S5lrUINYtGA0CTQ1sUXjowiYIfbqFIxPK9 nUat24/ksykBSb2BMwBB3ivIRcfOZNfJLiEEbOic= Date: Fri, 2 Dec 2022 13:38:40 -0800 From: Andrew Morton To: Mina Almasry Cc: Huang Ying , Yang Shi , Yosry Ahmed , Tim Chen , weixugc@google.com, shakeelb@google.com, gthelen@google.com, fvdl@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] mm: disable top-tier fallback to reclaim on proactive reclaim Message-Id: <20221202133840.5cdd4270cf73eaaa1d9d0345@linux-foundation.org> In-Reply-To: <20221201233317.1394958-1-almasrymina@google.com> References: <20221201233317.1394958-1-almasrymina@google.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: dgsdd9z1iu5obmsrcbkxjyabprgjw84q X-Rspam-User: X-Spamd-Result: default: False [0.98 / 9.00]; IRL_BL_25(2.00)[52.25.139.140:received]; BAYES_HAM(-1.62)[84.92%]; MV_CASE(0.50)[]; MIME_GOOD(-0.10)[text/plain]; RCVD_NO_TLS_LAST(0.10)[]; BAD_REP_POLICIES(0.10)[]; R_SPF_ALLOW(0.00)[+a:ams.source.kernel.org]; R_DKIM_ALLOW(0.00)[linux-foundation.org:s=korg]; RCPT_COUNT_SEVEN(0.00)[11]; FROM_EQ_ENVFROM(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; DKIM_TRACE(0.00)[linux-foundation.org:+]; RCVD_COUNT_THREE(0.00)[3]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_SOME(0.00)[]; DMARC_NA(0.00)[linux-foundation.org]; MID_RHS_MATCH_FROM(0.00)[]; ARC_SIGNED(0.00)[hostedemail.com:s=arc-20220608:i=1]; RCVD_VIA_SMTP_AUTH(0.00)[] X-Rspamd-Queue-Id: 350E118000E X-Rspamd-Server: rspam06 X-HE-Tag: 1670017124-765666 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 1 Dec 2022 15:33:17 -0800 Mina Almasry wrote: > Reclaiming directly from top tier nodes breaks the aging pipeline of > memory tiers. If we have a RAM -> CXL -> storage hierarchy, we > should demote from RAM to CXL and from CXL to storage. If we reclaim > a page from RAM, it means we 'demote' it directly from RAM to storage, > bypassing potentially a huge amount of pages colder than it in CXL. > > However disabling reclaim from top tier nodes entirely would cause ooms > in edge scenarios where lower tier memory is unreclaimable for whatever > reason, e.g. memory being mlocked() or too hot to reclaim. In these > cases we would rather the job run with a performance regression rather > than it oom altogether. > > However, we can disable reclaim from top tier nodes for proactive reclaim. > That reclaim is not real memory pressure, and we don't have any cause to > be breaking the aging pipeline. > Is this purely from code inspection, or are there quantitative observations to be shared?