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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1uoW2N-0000000E9dY-1uMv; Tue, 19 Aug 2025 23:46:43 +0000 Date: Wed, 20 Aug 2025 00:46:43 +0100 From: Matthew Wilcox To: Shakeel Butt Cc: Boris Burkov , akpm@linux-foundation.org, linux-btrfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, kernel-team@fb.com, wqu@suse.com, mhocko@kernel.org, muchun.song@linux.dev, roman.gushchin@linux.dev, hannes@cmpxchg.org Subject: Re: [PATCH v3 2/4] mm: add vmstat for cgroup uncharged pages Message-ID: References: <04b3a5c9944d79072d752c85dac1294ca9bee183.1755562487.git.boris@bur.io> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: qa59tca1ed1yfzpzzoracfagowsp5wpr X-Rspam-User: X-Rspamd-Queue-Id: EE7F220007 X-Rspamd-Server: rspam01 X-HE-Tag: 1755647207-6751 X-HE-Meta: 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 tUN2opZ6 x59tAnEocRii41L+uuaxkkAoykFD9jqc8dlwFmizKJvG0glNreqZRV9CD9pxRr1w7/pdy7B2Ysw2D49hubSpbyy26UIHGQJRKtr6KYk8V3SQEdYy7vMqlDwgLsVR9zoN6bJM6naEMCLnw5IFq3Y0YElh8NtlsKVm3ihD7Jd85gjKd0BsNLTDP1Xe8SQ== 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 Tue, Aug 19, 2025 at 08:53:59AM -0700, Shakeel Butt wrote: > My initial thinking was based on Qu's original proposal which was using > root memcg where there will not be any difference between accounted > file pages and system wide file pages. However with Boris's change, we > can actually get the estimate, as you pointed out, by subtracting the > number of accounted file pages from system wide number of file pages. > > However I still think we should keep this new metric because of > performance reason. To get accounted file pages, we need to read > memory.stat of the root memcg which can be very expensive. Basically it > may have to flush the rstat update trees on all the CPUs on the system. > Since this new metric will be used to calculate system overhead, the > high cost will limit how frequently a user can query the latest stat. OK, but couldn't we make that argument for anything else? Like slab, say. Why's "file" memory different?