From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 15864CCD183 for ; Thu, 16 Oct 2025 23:01:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0CA2B8E000D; Thu, 16 Oct 2025 19:01:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0A20E8E0006; Thu, 16 Oct 2025 19:01:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F20D38E000D; Thu, 16 Oct 2025 19:01:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id DD0328E0006 for ; Thu, 16 Oct 2025 19:01:13 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 1B8EE160419 for ; Thu, 16 Oct 2025 23:01:13 +0000 (UTC) X-FDA: 84005500026.29.A1A05B8 Received: from out-173.mta0.migadu.com (out-173.mta0.migadu.com [91.218.175.173]) by imf14.hostedemail.com (Postfix) with ESMTP id 943B6100018 for ; Thu, 16 Oct 2025 23:01:09 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=F81fm32C; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf14.hostedemail.com: domain of roman.gushchin@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1760655671; a=rsa-sha256; cv=none; b=kxvKFL01ZTz+ZrEJKyMuMwWlRu7i8MmbU8IZ9F0IvSC2yEz4maNDXpqsToTcYPaLIbrqFf tQ3lcVzozooPKctfnAajXAydkZcQjpTHwIWtsnXPBSvF9qc5e4YhZqAD3TrNPRcklF7oA0 qXXGKBJxvJd0Y92YukgpAtb+cJi+as4= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=F81fm32C; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf14.hostedemail.com: domain of roman.gushchin@linux.dev designates 91.218.175.173 as permitted sender) smtp.mailfrom=roman.gushchin@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1760655671; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=6lnf0SlVNBa1MHaoQqJyDwakLfgUyXqJdGj6LGOIvyI=; b=SrzDp35RO+pj+Ea7zJ2DlXlXbHLMgMuxM0bHVyu3CEDgAbBk8z7+nkBvcJTD91N3dKk2Va lAP4WdkJNkdGoow/Rrz49uSyZz42SKShUov0ecXh2NjOv2NRrCYI1PfGrINRZ206ULmPvC Zk2xyhSQ7fHVIMUkP5Uo/yo61BO/Tgw= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1760655667; 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=6lnf0SlVNBa1MHaoQqJyDwakLfgUyXqJdGj6LGOIvyI=; b=F81fm32Cy9ymkg8hRJwfUSBZlIddtx0rrYIvKNcMyGg30wqq+TDhJUAppy/zpkfR7sFmUK BzJxiPuQqKecd1ogb3moIZcub+cle2Sxur8YuNi1pZq//SzlgI1qC6Sn5lbVo6FSMWjAnW y/NyoB4mkR2VXNeGoRNPM9pqofHXBpU= 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: <2fa573e6-bd9a-46b9-a2a6-bfb233d0389a@gmail.com> (JP Kobryn's message of "Thu, 16 Oct 2025 13:26:44 -0700") References: <20251015190813.80163-1-inwardvessel@gmail.com> <87wm4v7isj.fsf@linux.dev> <2fa573e6-bd9a-46b9-a2a6-bfb233d0389a@gmail.com> Date: Thu, 16 Oct 2025 16:00:58 -0700 Message-ID: <87frbimoyd.fsf@linux.dev> MIME-Version: 1.0 Content-Type: text/plain X-Migadu-Flow: FLOW_OUT X-Stat-Signature: ju98coyda9qshqig7fg4j7u8wqhnd9tz X-Rspamd-Queue-Id: 943B6100018 X-Rspamd-Server: rspam06 X-Rspam-User: X-HE-Tag: 1760655669-230552 X-HE-Meta: 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 cMaRPayB 51FIWbtY2loNAFqDCg5GqhUG/47NFIL+1HPUSh1D9jGBIRX67qRz8CdTJOUnBh/rKBwSQApi/VTZW5BHEkmUvT3kg4rGBSA2jzPj4A1gIOd2JQeRBgl/Ue5sWGd2JEXTtRyjVoFq3LUjBBUiwPIG/bvS8YitGpMmdR65LUVbJNQ9AWVc8E3m6/+79BRCQYX+C/fy+l4EQMwst0ApkIoYI+ntU2v1N+ElSgTEL38va47AAYbpEP2cr4iwe3Q== 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 6:10 PM, Roman Gushchin wrote: >> 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. > > Sounds great. I see in your series that you allow the kfuncs to accept > integers as item numbers. Would my approach of using typed enums work > for you? I wanted to take advantage of libbpf core so that the bpf > program could gracefully handle cases where a given enumerator is not > present in a given kernel version. I made use of this in the > selftests. Good point, I'm going to change it in the next version, which I'm about to send out: tomorrow or early next week. > I'm planning on sending out a v3 so let me know if you would like to see > any alterations that would align with bpfoom. I kinda prefer my version regarding taking a memcg argument instead of cgroup and also regarding naming. I also think it's safer to expose the rate-limited version of stats flushing function. But I do lack the node-level statistics (which I don't need) If it's ok with you, maybe you can rebase your patches on top of my v2 and I can include your patches in the series? Thanks!