From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87F2039A802 for ; Fri, 24 Jul 2026 06:54:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784876049; cv=none; b=Rb+L0c5BhKRdjaKueKlhAnCFO2fCd68PdDQWwvUIeak4ZpEsHbbeYlKpBXb9f22L6/gXRvbyRk8csdOHkLsrlQS3Fa8SDnNG9U/Rkd1nWdyOP8xf4mnTAkGOvmj+oA4BQ0luobVfcFXXP/C2kecW8eMpaXNA3AIHFFcZDT84udQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784876049; c=relaxed/simple; bh=/CdbwamX7b1IPnTJkU8yoaf5INqtkxYtv3QoCf/xKf0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hDZYU3Fu/sJg6M7KlPkrE+lZsQRg2PIRHR3vkp5Qd38gY/uieyBup6qtiUr+WCAJ0DbXtnJ9rrBLEK7a0lGyiYt7VLq4yuKNBVBsP6cu4kBgaHWBlBCtQ2O3mG2v8Kg1R0R2NBZ2XIiQsIathx2CRsMt2cNUvjzaLb4iCIErUnM= 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=fKcoAGrr; arc=none smtp.client-ip=95.215.58.186 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="fKcoAGrr" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784876031; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=APONQVsPJkkQx8mNtrNVFM4P3UKPMmWHeB8nUygzPiE=; b=fKcoAGrrAnA635Yh9d/uLCwMRNa9LD5bxnO4YgA2+uFrLRy0La+iXderjPvz4yoAv3efz8 Z8yOoE74pSaM0nn1NfQT2Gr9E7SPCtWd1jupNsaGo0G/ZfD7GxHXuOCCRbxT3+WrZTma1T X+pi5BI/4WATlWg0CzclnMNkKhRpus0= Date: Fri, 24 Jul 2026 14:53:29 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] mm: memcg: stop reclaim when a limit update is superseded To: Tao Cui , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Andrew Morton Cc: Muchun Song , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Guopeng Zhang References: <20260724021805.1234583-1-guopeng.zhang@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Guopeng Zhang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 在 2026/7/24 11:32, Tao Cui 写道: > > > 在 2026/7/24 10:18, Guopeng Zhang 写道: >> From: Guopeng Zhang >> >> kernfs serializes file operations only per open file, so separate open >> files can update the same memory.high or memory.max file concurrently. >> Both handlers store the new limit before synchronous reclaim, but >> continue to use the writer's local target in the reclaim loop. If another >> writer raises or removes the limit, the first writer can continue >> reclaiming toward a stale target. >> >> For memory.max, this can leave the writer looping indefinitely once >> reclaim retries are exhausted. The OOM path sees sufficient margin under >> the current limit and returns true without killing, while the writer >> still compares usage against its stale target and records another OOM >> event. >> >> Check the current limit at the start of each reclaim iteration and stop >> if it no longer matches the writer's target. >> > > Fix looks correct to me. > > Acked-by: Tao Cui > > Nit: the message lumps both paths together, but only memory.max loops > indefinitely. memory.high has no OOM path, so it just spins > MAX_RECLAIM_RETRIES times and breaks on its own. Worth a line to avoid > conflating the severity. > Hi, Thanks for the review and Ack. The message separates the two cases: the first paragraph describes the stale-target reclaim behavior common to both, while the "For memory.max" paragraph describes the OOM-based indefinite loop. One detail is that memory.high is not limited to MAX_RECLAIM_RETRIES iterations. The retry counter is decremented only when reclaim makes no progress: if (!reclaimed && !nr_retries--) break; If reclaim continues to make progress while pages are refaulted, nr_retries is not decremented and the loop can still fail to converge. Thanks, Guopeng >> Fixes: 8c8c383c04f6 ("mm: memcontrol: try harder to set a new memory.high") >> Fixes: b6e6edcfa405 ("mm: memcontrol: reclaim and OOM kill when shrinking memory.max below usage") >> Signed-off-by: Guopeng Zhang >> --- >> Reproducer: >> >> Populate a cgroup with anonymous memory and disable swapping. Lower >> memory.max from one open file, then restore it to "max" through another >> open file after the new limit becomes visible. >> >> Without the patch, the first writer remains blocked and repeatedly >> increments the OOM event counter. With the patch, it returns normally. >> >> mm/memcontrol.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 8319ad8c5c23..638bdc766616 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -4798,6 +4798,9 @@ static ssize_t memory_high_write(struct kernfs_open_file *of, >> unsigned long nr_pages = page_counter_read(&memcg->memory); >> unsigned long reclaimed; >> >> + if (high != READ_ONCE(memcg->memory.high)) >> + break; >> + >> if (nr_pages <= high) >> break; >> >> @@ -4853,6 +4856,9 @@ static ssize_t memory_max_write(struct kernfs_open_file *of, >> for (;;) { >> unsigned long nr_pages = page_counter_read(&memcg->memory); >> >> + if (max != READ_ONCE(memcg->memory.max)) >> + break; >> + >> if (nr_pages <= max) >> break; >> >