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b=dziK+806lLO8VOlSVfWwwNC7nX16u6KwSZcl0IA6qeAtr5PUBrbfTqIMgqv2XRIxm AeuhbSVI+w9EmPd6anomHOTrsK3G2n+9JypqKfwnHtlo0g0GbaDVOgxkMUd9kZfdc1 StMbQ3RbN1ENgmKKY0C7s4BNV0izatm5eb5CYB+4= Date: Thu, 8 Aug 2024 16:20:11 -0700 From: Andrew Morton To: Gregory Price Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@redhat.com, ying.huang@intel.com, nphamcs@gmail.com, nehagholkar@meta.com, abhishekd@meta.com Subject: Re: [PATCH 0/3] mm,TPP: Enable promotion of unmapped pagecache Message-Id: <20240808162011.0492099266ac47e7b84eacd0@linux-foundation.org> In-Reply-To: <20240803094715.23900-1-gourry@gourry.net> References: <20240803094715.23900-1-gourry@gourry.net> X-Mailer: Sylpheed 3.7.0 (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-Stat-Signature: ru84c4xf86xkw5baxtgzrrbfx38yea51 X-Rspamd-Queue-Id: 40B6D140008 X-Rspamd-Server: rspam11 X-HE-Tag: 1723159214-433036 X-HE-Meta: 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 1yP0VkAY eoCneJx+cCTd5nMjFykh3L5JAPzWy9S7c0n2PEoDlFyeI/gpI3PCfrayOyfL39SbogfTmfeiOMMjAXjCyEko2s0XSGDO8Wb+ZoBmnHNJIqZRDiAmqHf7qv69++TViNWM/Bdn67qvBVrWTmv3VLqztCL1DRPbEFLY5pJYL9f6SDA6LuZoAEohKjpcTZxnHLhOj4jOMkK0SlVHQDdPacL633XDPg/vrPpyR2T/YmQIn/b8mwP1ZOxETFvzbkbWjlXlLb9dnQxBFRMwtSa0uuf+xSbW8VzQUqi45gS9X 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: List-Subscribe: List-Unsubscribe: On Sat, 3 Aug 2024 05:47:12 -0400 Gregory Price wrote: > Unmapped pagecache pages can be demoted to low-tier memory, but > they can only be promoted if a process maps the pages into the > memory space (so that NUMA hint faults can be caught). This can > cause significant performance degradation as the pagecache ages > and unmapped, cached files are accessed. It would be helpful to share some testing results so the magnitude of this degradation can be understood. What is the potential downside to this change? The local node now gets stuffed full of pagecache and other things get evicted? > This patch series enables the pagecache to request a promotion of > a folio when it is accessed via the pagecache. > > We add a new `numa_hint_page_cache` counter in vmstat to capture > information on when these migrations occur.