From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-221.mta0.migadu.com [91.218.175.221]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 79A0F3ACEE3 for ; Thu, 20 Aug 2026 08:43:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.221 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787215419; cv=none; b=CV+VnYhfGwNvz8n7aBqKXxaxVKxfJIuUTp5TyrVKjP/43WLhiRmjqYrWK9su1r+l9dhW592PXB0yK9AEw3+Z13L9yzhxd45VM7pUmnDIQHFB34RhS9mjTPkPHEkQgzVjx1RWoXyWcI4ebk4ieoszYdkYD3b+yY3oSGld8PkLQwQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787215419; c=relaxed/simple; bh=yTjYhvKkMHDo9qLLabTyUV3J3cL/wvyOOWOBN5nhYWo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZL28JJSBXFYDTCjtc3AnJ71W6SkeVGo3Pkn0z/1aTytzq76Vdad+bmmvJd4wfiFHQXvjxOdfWp7FQKJtLSO304hJv2Y8Fa9UWDyzJjThknL6icIPfjghdLVBvzNMqx6sqBHqyxI3Qse1uNsP4Ml44Urn+alNAWhglz2CQwwef10= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=XStD9AlN; arc=none smtp.client-ip=91.218.175.221 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="XStD9AlN" X-Envelope-To: cgroups@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=yTjYhvKkMHDo9qLLabTyUV3J3cL/wvyOOWOBN5nhYWo=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787215415; v=1; x=1787820215; b=XStD9AlN2vwxKH/blq7pNCqOEL8amlojWvPjAb3wCg/FZCrQhmsbmF9XlBqxSgj3hMe4pvOV PV3CVYNKEHMWJ8TsH4YheOf+VYIy8LtftbzPMevvEFDnE3/8E8g8omazPcXCdJwNacF/hGE5hn6 S9hgxjwprJI0uMlEmYsjy6uQ= X-Envelope-To: cgroups@vger.kernel.org Received: from [10.63.107.123] (14.29.108.92) by smtp.migadu.com with ESMTPS id 50b587144d94fa93; Thu, 20 Aug 2026 08:43:35 +0000 X-Mizu-Trace-ID: 50b587144d94fa93 X-Migadu-Flow: FLOW_OUT Message-ID: Date: Thu, 20 Aug 2026 16:43:23 +0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 0/2] mm, memcg: fix memory.peak reset clobbering other fds' watermark To: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton Cc: Muchun Song , David Finkel , Tejun Heo , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , "open list:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" , linux-kernel@vger.kernel.org, Tao Cui , Ridong Chen References: <20260814033005.2481920-1-ridong.chen@linux.dev> From: Ridong Chen In-Reply-To: <20260814033005.2481920-1-ridong.chen@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/14/2026 11:30 AM, Ridong Chen wrote: > From: Ridong Chen > > The memory.peak / memory.swap.peak per-fd watermark tracking has two > issues. Each open fd is a watcher and reads back max(its own value, the > shared local_watermark); both bugs live in that scheme. > > Worst case for both is the same and is userspace-visible: a reader of > memory.peak (or memory.swap.peak) gets a value lower than the true peak, > so a tool that sizes or bills a cgroup by its peak usage under-reports it. > > Patch 1 (read side) fixes the race Sashiko pointed out in the v1 review > [1]: peak_show() inspects local_watermark and the per-fd values without > holding peaks_lock, so a reader that races an unrelated peak_write() > reset briefly observes the lowered value. Transient. It takes peaks_lock > in the show path. > > Patch 2 (write side) fixes peak_write(): on a reset it stores the > current usage into the other watchers instead of the old watermark, so > once usage has dropped from a peak a reset on one fd drags every other > fd's peak down too, even fds that never reset. > > --- > Changes since v3: > - Switch to guard(spinlock) in the peak readers, suggested by Muchun. > > Changes since v2: > - Spell out the worst-case userspace-visible effect, per Andrew's > Go back to v1 [2]. > > Changes since v1: > - New patch 1: hold peaks_lock in the peak readers (Sashiko). > - Patch 2: floor the peers with max(usage, local_watermark), mirroring > peak_show(), and skip the writing fd (Johannes Weiner). > > [1] https://sashiko.dev/#/patchset/20260730115314.1069089-1-ridong.chen@linux.dev?part=1 > [2] https://lore.kernel.org/all/20260730115314.1069089-1-ridong.chen@linux.dev/ > > Ridong Chen (2): > memcg: acquire peaks_lock when reading memory.peak > mm, memcg: fix memory.peak reset clobbering other fds' watermark > > mm/memcontrol.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > Hi all, Just a quick reminder on this series, could it be applied? Sending this note in case it got buried. -- Best regards Ridong