From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out199-15.us.a.mail.aliyun.com (out199-15.us.a.mail.aliyun.com [47.90.199.15]) (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 ABFFB378D94 for ; Thu, 26 Mar 2026 02:28:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=47.90.199.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774492088; cv=none; b=Ka10IxJnxuaKlGoWbWuYZ+B/1GXUqniwQVXaicW17D+fqHcwUiBeOGOOJLDeDotTPjXvVud2yCAjY/uV29/C1eek+j3kTVSQd2LzKH8ODVeKFOP14l36XYUyrCuIoXxjN9EtGtmEkihv0HCpq+55ZKPyYS3rQQWPc766PDF3zZM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774492088; c=relaxed/simple; bh=LWcgMusfuwdvOSVvgmz5J0E060iwVCtuwMkrzZ9//5E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=JyG/dYJuXcjW7NcxQXUYJYDOafY0ZpETS2jMFBI28KwSaFutuVBL+34n6Sofr7JDkRgAgBWq8TjXfipOUhQCWER2P7Ph40bP2VJkuegdqtywEO6H/8T+WFzTNhLoDqXkim2JK1qG4vhh8wodweUI2Gc5HzRjqt+BUKe4a7AiWDU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=IAlEMiIb; arc=none smtp.client-ip=47.90.199.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="IAlEMiIb" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1774492080; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=4P3HZeFpAYcP9fuDTLYiiV3smE1BlqrAdg4KKIFqogo=; b=IAlEMiIbtryU4q0YsvD02SJd9uSR4LVFtlx4HdHMQ8dTgnsmXUYYxXRQuax2tcZBC55yLUr0lsMWFItYwJC5QfgyzEuMQZ1dnIhv3+7ZdohOPY2Xbs0db1W9lLf5f/R5yx5lZUCxB6Pr7UcoQDG2NchkzxzoxE8XQ3V4V+AbwTM= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045098064;MF=baolin.wang@linux.alibaba.com;NM=1;PH=DS;RN=15;SR=0;TI=SMTPD_---0X.jkM2T_1774490239; Received: from 30.74.144.123(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0X.jkM2T_1774490239 cluster:ay36) by smtp.aliyun-inc.com; Thu, 26 Mar 2026 09:57:19 +0800 Message-ID: <035e7e83-1811-4f8d-b8ed-0f5025e66399@linux.alibaba.com> Date: Thu, 26 Mar 2026 09:57:18 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: vmscan: fix dirty folios throttling on cgroup v1 for MGLRU To: Kairui Song Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, david@kernel.org, mhocko@kernel.org, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, baohua@kernel.org, kasong@tencent.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Lorenzo Stoakes (Oracle)" References: From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/25/26 9:35 PM, Kairui Song wrote: > On Wed, Mar 25, 2026 at 09:20:55PM +0800, Baolin Wang wrote: >> Hi Kairui, >> >> On 3/25/26 8:07 PM, Kairui Song wrote: >>> On Wed, Mar 25, 2026 at 07:50:40PM +0800, Baolin Wang wrote: >>>> The balance_dirty_pages() won't do the dirty folios throttling on cgroupv1. >>>> See commit 9badce000e2c ("cgroup, writeback: don't enable cgroup writeback >>>> on traditional hierarchies"). >>>> >>>> Moreover, after commit 6b0dfabb3555 ("fs: Remove aops->writepage"), we no >>>> longer attempt to write back filesystem folios through reclaim. >>>> >>>> On large memory systems, the flusher may not be able to write back quickly >>>> enough. Consequently, MGLRU will encounter many folios that are already >>>> under writeback. Since we cannot reclaim these dirty folios, the system >>>> may run out of memory and trigger the OOM killer. >>>> >>>> Hence, for cgroup v1, let's throttle reclaim after waking up the flusher, >>>> which is similar to commit 81a70c21d917 ("mm/cgroup/reclaim: fix dirty >>>> pages throttling on cgroup v1"), to avoid unnecessary OOM. >>>> >>>> The following test program can easily reproduce the OOM issue. With this patch >>>> applied, the test passes successfully. >>>> >>>> $mkdir /sys/fs/cgroup/memory/test >>>> $echo 256M > /sys/fs/cgroup/memory/test/memory.limit_in_bytes >>>> $echo $$ > /sys/fs/cgroup/memory/test/cgroup.procs >>>> $dd if=/dev/zero of=/mnt/data.bin bs=1M count=800 >>>> >>>> Signed-off-by: Baolin Wang >>>> --- >>>> mm/vmscan.c | 13 ++++++++++++- >>>> 1 file changed, 12 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>> index 33287ba4a500..a9648269fae8 100644 >>>> --- a/mm/vmscan.c >>>> +++ b/mm/vmscan.c >>>> @@ -5036,9 +5036,20 @@ static bool try_to_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) >>>> * If too many file cache in the coldest generation can't be evicted >>>> * due to being dirty, wake up the flusher. >>>> */ >>>> - if (sc->nr.unqueued_dirty && sc->nr.unqueued_dirty == sc->nr.file_taken) >>>> + if (sc->nr.unqueued_dirty && sc->nr.unqueued_dirty == sc->nr.file_taken) { >>>> + struct pglist_data *pgdat = lruvec_pgdat(lruvec); >>>> + >>>> wakeup_flusher_threads(WB_REASON_VMSCAN); >>>> + /* >>>> + * For cgroupv1 dirty throttling is achieved by waking up >>>> + * the kernel flusher here and later waiting on folios >>>> + * which are in writeback to finish (see shrink_folio_list()). >>>> + */ >>>> + if (!writeback_throttling_sane(sc)) >>>> + reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK); >>>> + } >>>> + >>>> /* whether this lruvec should be rotated */ >>>> return nr_to_scan < 0; >>>> } >>> >>> Hi Baolin >>> >>> Interesting I want to fix this too, after or with: >>> https://lore.kernel.org/linux-mm/20260318-mglru-reclaim-v1-0-2c46f9eb0508@tencent.com/ >> >> Thanks for taking a look. >> >>> >>> With current fix you posted, MGLRU's dirty throttling is still >>> a bit different from active / inactive LRU. In fact MGLRU >>> treat dirty folios quite differently causing many other issues too, >>> e.g. it's much more likely for dirty folios to stuck at the tail >>> for MGLRU so simply apply the throttling could cause too >>> aggressive throttling. Or batch is too large to trigger the >>> throttling. >> >> Thanks for sharing this. > > Hi Baolin, > >> >>> So I'm planning to add below patch to V2 of that series (also this >>> is suggested by Ridong), how do you think? There are several >>> other throttling things to be fixed too, more than just the >>> V1 support. I can have your suggested-by too. >> >> But I still think this fix deserves its own commit, because this is indeed >> fixing a real issue that I ran into. Even if the throttling isn't perfect >> for cgroup v1, it aligns with the legacy-LRU behavior and is essential to >> avoid premature OOMs firstly. MGLRU dirty folio handling improvement can be >> done as a separate optimization in your series. >> >> Anyway, let's also wait for more feedback from others. >> > > Sure, fixing this first is fine to me, just saying that you may > still see unexpected throttling or ineffective throttling with this. > > This is no conflict between these two approach. I can rebase that > series on top of yours, and that series would help to solve the > rest of issues. OK. Thanks.