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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1760577060; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=9eWglOj1q+AvMecMj1okWvapeunhbN56i+AV+BTzGlg=; b=UjNeyfN1lT1QbHQB+SBjn0crZxw3AICe3s9vXl69EmVdsbWMGRugblFUU+RtOSrApnbuYn qsCHcCG9o2C7orU+K/C7S5ix0iMllM0rqLx3c0zQqw3cXquoFBBCtvZMdJqdhRfToEAkVd 8vY7AV0p6MJ6tuTF+BMvv/UuTc+Bd7M= From: Roman Gushchin To: JP Kobryn Cc: Shakeel Butt , andrii@kernel.org, ast@kernel.org, mkoutny@suse.com, yosryahmed@google.com, hannes@cmpxchg.org, tj@kernel.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, kernel-team@meta.com, mhocko@kernel.org, muchun.song@linux.dev Subject: Re: [PATCH v2 0/2] memcg: reading memcg stats more efficiently In-Reply-To: (JP Kobryn's message of "Wed, 15 Oct 2025 17:21:46 -0700") References: <20251015190813.80163-1-inwardvessel@gmail.com> Date: Wed, 15 Oct 2025 18:10:52 -0700 Message-ID: <87wm4v7isj.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT X-Stat-Signature: z756e4b9d9pe9aokxynw9zg3zxziois9 X-Rspamd-Queue-Id: B67D740005 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1760577062-722929 X-HE-Meta: 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 pRG/MQoR /aHYMDJU0Dz/40rHo/jzopqgmmZtQw9/hOOIH4G5GPzlsMaF/sx09CKdLRYLRoLQTnK1BHsYKTSFu9NYdV3rZfJo2hMn6WizFK86qRp8MsikrAeMi+CRZGve4MPQh4FtfDadLf5o1hBuF1paG17bowIax27+JimW1RYXbTSWMb2S9EODncOHCybgduucFI1MWQ5Ub6J08tySKioRZvCz4rc43NZM91hIc1l45rFPdKzLa0cHt/RPZpjv2Kw== 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: JP Kobryn writes: > On 10/15/25 1:46 PM, Shakeel Butt wrote: >> Cc memcg maintainers. >> On Wed, Oct 15, 2025 at 12:08:11PM -0700, JP Kobryn wrote: >>> When reading cgroup memory.stat files there is significant kernel overhead >>> in the formatting and encoding of numeric data into a string buffer. Beyond >>> that, the given user mode program must decode this data and possibly >>> perform filtering to obtain the desired stats. This process can be >>> expensive for programs that periodically sample this data over a large >>> enough fleet. >>> >>> As an alternative to reading memory.stat, introduce new kfuncs that allow >>> fetching specific memcg stats from within cgroup iterator based bpf >>> programs. This approach allows for numeric values to be transferred >>> directly from the kernel to user mode via the mapped memory of the bpf >>> program's elf data section. Reading stats this way effectively eliminates >>> the numeric conversion work needed to be performed in both kernel and user >>> mode. It also eliminates the need for filtering in a user mode program. >>> i.e. where reading memory.stat returns all stats, this new approach allows >>> returning only select stats. It seems like I've most of these functions implemented as part of bpfoom: https://lkml.org/lkml/2025/8/18/1403 So I definitely find them useful. Would be nice to merge our efforts. Thanks!