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 81FE0D358E5 for ; Thu, 29 Jan 2026 08:51:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A867A6B0088; Thu, 29 Jan 2026 03:51:21 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A3A166B0089; Thu, 29 Jan 2026 03:51:21 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9163E6B008A; Thu, 29 Jan 2026 03:51:21 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 81DFC6B0088 for ; Thu, 29 Jan 2026 03:51:21 -0500 (EST) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 2F8A9160920 for ; Thu, 29 Jan 2026 08:51:21 +0000 (UTC) X-FDA: 84384382362.18.55C8184 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) by imf08.hostedemail.com (Postfix) with ESMTP id 366A9160004 for ; Thu, 29 Jan 2026 08:51:18 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=vvxYXiUm; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf08.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1769676679; a=rsa-sha256; cv=none; b=hZKFvyU6eDVcgoyww9SPGkWEYGoWDyiSSwidK6j+mEq1n5rhYosfb/TceTxQzPXP3OrodT t7B6qAWMaHJu/LsCcpOxeHQcgaKfCOUK5XUf9KKOxRYM8PN9P87PR5IcM5yDS5/0nsx3cA xySTmDpTR/Hh8qlZieBzIvtnhP5IjeM= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=vvxYXiUm; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf08.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.182 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1769676679; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=uAdXb4bfUsmEDEKXvxCCDPoLM2r4WzvPltJYWV3bwtA=; b=H9GsN9NiQkcXQW1tMjI1rxjonXlb5mi+6dXQ+bPr0GBn74Go9r8kwyLvsHQmtUTRSInwLL GnbZPkdEO0v3mnYStBhvNaiMMMHW2Ad5s7EnPhFYPOnRqxnmizbamwoW0nn4IawaqWcwkT 0mMhUDbLBxqFvg/wuKfrUpTwY10M4Tk= Message-ID: <6860146b-be12-4d5f-bec1-bbcec1dffbc6@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1769676676; 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=uAdXb4bfUsmEDEKXvxCCDPoLM2r4WzvPltJYWV3bwtA=; b=vvxYXiUm1xh5hSI0HndFd1wGYWaZAXe1kxDlslz5niCHLt+NR7Yn1ohQi7vhPZBTvXJ7mV 1TOrUgLmqGZQW99e0EBT4XQfvagxB0MBQuERtxdBLv5eBFvZmMTRRTrcUfg5c03zZwDx1O c0M/oTunUTmd9zvO4CMOmjcmhXbsWRo= Date: Thu, 29 Jan 2026 16:50:39 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v3 28/30] mm: memcontrol: prepare for reparenting state_local To: Harry Yoo Cc: Shakeel Butt , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, muchun.song@linux.dev, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, yosry.ahmed@linux.dev, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Qi Zheng References: <9b9057f8-4c4c-4067-b6ba-0791888c25e8@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 366A9160004 X-Stat-Signature: qgif1jhpbj4959pxa4mnk6q53awcqtq6 X-HE-Tag: 1769676678-270942 X-HE-Meta: U2FsdGVkX1+jLdmsiLsBi0rMZs8yyeBc++p47xvrxYxIOKlkI+SWz9KZ0CFvLYaIUxP7frdhXsrB0wThT4EbG71itbnhKoT2MCbHCWAz935elWbNwo11EesG5P7UxijDmPbziIbWgz3nUPdVCTysdeVGnDJqFZtcp1gXDE9Tb8N852AmoVKVy2OsA5FYJGQrMJy7UmHVo2w6IbPqdz7139Wmy2KhwbpuqIvhrOK2eNkDtL4UPjPlEIkNpv3k+++IxIBvoI9Q5+o4yvKZYVOpcLVN/ltd1E2XP7hPN8cOlf0srINV+3D6OqRoMCDuKK3rB6quBYPw+5slTooowHpDGL61jDiTBjdV67u5C05SlthPgQhFDnbNePo/akVkN1O9FLYlR4ylODO+Bc4MKLQwL35UKRrbxtd5s7HJ7ScIpNjA9aK3+MJGcnr2MKyMwhjEjp8iqE2aJUqR9dXBSdvLamSldA3YZ12VNxREvGzCD+cc/DZz7GvLhgu64oVL8Mzjhx3enZWZ9qZjdncTlxlLekmKutYo34Zm7ZBrdmeQH75LqYJ7TgnBTP3xSzL77ZSVTrMtdKZoe5OcM6AjCnx50HNwXw9LgbzhqcwZX0ziAV37yq/DuMYzPJeFISMVrVVk52NgNeD4SNeWXjgela6+u6n/qWKjSkfz7+K2xkGUUTeLZ+hUK8PNXCH35vkBer++bfBLrSbp1ww2K1YSO26JIUZa7VSwg2K18CvIwEU2o0LX0wCYTwWzlFL9RZRgA05U65+oTsaxEiQeQuMtZpOR4h+D2z1VyDIhNVRZgTeF5tH/yZ4fyN4oqEe9Qc2pRrws5g5X5ytt9Mck0Y+nTuq1s6zn/HisqT1ZZxde2Ic6KHunCpwlMkTQlBLfAqB2YTAbNiZXtQMyhQVCFfSCd+wVh5knqrKCVTn9aPUEZrQZdgZMJh5drOEPT6aGJMsSmOIEcofpo4ibcsh7GyE9OSL woDIDrmF hbXQa0B0/tovYn29vBMds2nFeIA0X+vIR4ZN3gCpsZQeW4VkPGkHi8gMlUJJp2pmQAqrftlPQCC3mmKFGOXUycoSynSXRkEWNR3Er0YoGJqxnh2raq6f27EGKUqe48/CgizhuUlroQxwmJffQI//2qqZ7YKBjSL+JIibEqIQGLRg8QVx3c/g8Vs0d5vP017QEvXJ6ay/OtAa0X+q/CwC9RZwW7H5PqNDhfuXeW1JgqYsy5FImMhpRfRn5xKH4oq1sM4DiZFZkeqJaWqYl2enWfSlAPxZnLdTgrw3GWJS2O+z1hb0= 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: On 1/29/26 10:10 AM, Harry Yoo wrote: > On Mon, Jan 19, 2026 at 11:34:53AM +0800, Qi Zheng wrote: >> >> >> On 1/18/26 11:20 AM, Shakeel Butt wrote: >>> On Wed, Jan 14, 2026 at 07:32:55PM +0800, Qi Zheng wrote: >>>> From: Qi Zheng >>>> >>>> To resolve the dying memcg issue, we need to reparent LRU folios of child >>>> memcg to its parent memcg. The following counts are all non-hierarchical >>>> and need to be reparented to prevent the counts of parent memcg overflow. >>>> >>>> 1. memcg->vmstats->state_local[i] >>>> 2. pn->lruvec_stats->state_local[i] >>>> >>>> This commit implements the specific function, which will be used during >>>> the reparenting process. >>> >>> Please add more explanation which was discussed in the email chain at >>> https://lore.kernel.org/all/5dsb6q2r4xsi24kk5gcnckljuvgvvp6nwifwvc4wuho5hsifeg@5ukg2dq6ini5/ >> >> OK, will do. >> >>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>>> index 70583394f421f..7aa32b97c9f17 100644 >>>> --- a/mm/memcontrol.c >>>> +++ b/mm/memcontrol.c >>>> @@ -225,6 +225,28 @@ static inline struct obj_cgroup *__memcg_reparent_objcgs(struct mem_cgroup *memc >>>> return objcg; >>>> } >>>> +#ifdef CONFIG_MEMCG_V1 >>>> +static void __mem_cgroup_flush_stats(struct mem_cgroup *memcg, bool force); >>>> + >>>> +static inline void reparent_state_local(struct mem_cgroup *memcg, struct mem_cgroup *parent) >>>> +{ >>>> + if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) >>>> + return; >>>> + >>>> + synchronize_rcu(); >>> >>> Hmm synchrinuze_rcu() is a heavy hammer here. Also you would need rcu >>> read lock in mod_memcg_state() & mod_memcg_lruvec_state() for this >>> synchronize_rcu(). >> >> Since these two functions require memcg or lruvec, they are already >> within the critical section of the RCU lock. > > What happens if someone grabbed a refcount and then release the rcu read > lock before percpu refkill and then call mod_memcg[_lruvec]_state()? > > In this case, can we end up reparenting in the middle of non-hierarchical > stat update because they don't have RCU grace period? > > Something like > > T1 T2 > > - rcu_read_lock() > - get memcg refcnt > - rcu_read_unlock() > > - call mod_memcg_state() > - CSS_IS_DYING is not set > - Set CSS_IS_DYING > - Trigger percpu refkill > > - Trigger offline_css() > -> reparent non-hierarchical - update non-hierarchical stats > stats > - put memcg refcount Good catch, I think you are right. The rcu lock should be added to mod_memcg_state() and mod_memcg_lruvec_state(). I will update to v4 as soon as possible. Thanks, Qi > >>> Hmm instead of synchronize_rcu() here, we can use queue_rcu_work() in >>> css_killed_ref_fn(). It would be as simple as the following: >> >> It does look much simpler, will do. >> >> Thanks, >> Qi >