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 6AB81C43458 for ; Fri, 10 Jul 2026 06:19:31 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2DC5C6B008C; Fri, 10 Jul 2026 02:19:30 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 28D326B0092; Fri, 10 Jul 2026 02:19:30 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 17EC06B0093; Fri, 10 Jul 2026 02:19:30 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id D92F06B008C for ; Fri, 10 Jul 2026 02:19:29 -0400 (EDT) Received: from smtpin15.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 4230A14038C for ; Fri, 10 Jul 2026 06:19:29 +0000 (UTC) X-FDA: 84971865258.15.9F349DA Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) by imf01.hostedemail.com (Postfix) with ESMTP id 1576040007 for ; Fri, 10 Jul 2026 06:19:26 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=K4rbRarg; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf01.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.181 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=1783664367; 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=DrsFrXe2gSCY+3C8A2OllD1L02A+ogsgIvQEHN3LEIs=; b=uK+Vzv0AAT8zPs7jUwh+qD3h1yu9p+m2FDWw8vku10tKzDaRYGhh/vBCdE2y1eQoCEImQE FkDPKh2IcB5MOO26vtu5Y0y4Ic2eXAw7DeMMOtTILVJBF6S4nuflpp8Lh2mXxfeiBXfMHu 5hW9Z0pkYlZMTXIafLDSgkLkJGv4f9U= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=K4rbRarg; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf01.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.181 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1783664367; b=lt+hIiML3TJK3i7dSS6k1OlnE2jIyfyy3cP70Vc2H0K5hVXYxYnfOfGN847zn9kWfpxwiX Mf0V/DsBSDUyceN6MXQ2gk4qJOC7Q7iJr/KbASpQVl+dYcdoeELb4ZOS+9im8M7xYnglGm kybAneI7oNYkJmoxn1SLWQUTvaAe6ak= Message-ID: <843f6d0d-e893-43ef-9cb3-1df21fb64b8d@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783664364; 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=DrsFrXe2gSCY+3C8A2OllD1L02A+ogsgIvQEHN3LEIs=; b=K4rbRargGu/1m7H7J1KlcEYwGgrEC/POAKdRi4IsE48sycrNl9n81QN99X5HnfmKV6pmcQ fysIWrFwHA85OWdrNsqN2XQV4xNxuSTFJBomRbesKeVzqYeissHyYD0AuQwjYYtYqTpCTE WW8SbGhVvnSDt+IBBP6XoZbP7zvPIcE= Date: Fri, 10 Jul 2026 14:19:15 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v4] mm: mglru: fix stale batch updates after memcg reparenting To: Johannes Weiner Cc: Harry Yoo , Usama Arif , akpm@linux-foundation.org, david@kernel.org, kasong@tencent.com, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, muchun.song@linux.dev, peiyang_he@smail.nju.edu.cn, mhocko@kernel.org, roman.gushchin@linux.dev, ljs@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng , stable@vger.kernel.org References: <20260701145736.3785016-1-usama.arif@linux.dev> <2fb5ce53-666b-4b0a-a4ad-2b3a28c54768@kernel.org> 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-Stat-Signature: o1nzdj1sepw7wmtq15pwg86c7kdgk7ia X-Rspamd-Queue-Id: 1576040007 X-Rspamd-Server: rspam01 X-Rspam-User: X-HE-Tag: 1783664366-927408 X-HE-Meta: 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 65HNQUsU glVDqjVwj1PXmAsOmqoU75hwCg8dEiYg1xfJUcQZoEKYFhoZj+4WKO27D6vWzUltXq/0Sokp/MDACaqcA2L3SIK0h7PHGmED8czOnvU4oKisxpKIxaggvi173qBWFYO4of7FJ0fEkJ1mLxSoWY3YHHl8VTG9DW8rmA2eq80PZ0HTbwoqK1mPt34Dc0V2XYA+cnbx0dpYQMmWCp2z1IfU2OMAi+wfY77nswM+45+Iq1vKMSPheKd8lDmr3dMlLp1/2H6xb Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/10/26 9:51 AM, Johannes Weiner wrote: > On Thu, Jul 02, 2026 at 09:38:41AM +0800, Qi Zheng wrote: >> >> >> On 7/1/26 11:59 PM, Johannes Weiner wrote: >>> On Thu, Jul 02, 2026 at 12:36:42AM +0900, Harry Yoo wrote: >>>> >>>> >>>> On 7/1/26 11:57 PM, Usama Arif wrote: >>>>> On Wed, 1 Jul 2026 15:52:51 +0800 Qi Zheng wrote: >>>>> >>>>>> From: Qi Zheng >>>>>> >>>>>> The mglru page table walker batches per-generation size deltas in >>>>>> walk->nr_pages while walking page tables without holding the lruvec lock. >>>>>> The reset_batch_size() later folds those deltas into walk->lruvec under >>>>>> the lruvec lock. >>>>>> >>>>>> The page table walker can run concurrently with the memcg reparenting path >>>>>> as follows: >>>>>> >>>>>> CPU0 CPU1 >>>>>> ==== ==== >>>>>> >>>>>> walk_mm >>>>>> --> walk_page_range >>>>>> --> update_batch_size >>>>>> --> walk->nr_pages += delta >>>>>> >>>>>> mem_cgroup_css_offline >>>>>> --> memcg_reparent_objcgs >>>>>> --> lock lruvec >>>>>> lru_gen_reparent_memcg >>>>>> --> reparent child folios to parent >>>>>> unlock lruvec >>>>>> >>>>>> lock lruvec >>>>>> reset_batch_size >>>>>> --> child lrugen->nr_pages += delta >>>>>> >>>>>> This will trigger the following warning in lru_gen_exit_memcg(): >>>>>> >>>>>> VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, >>>>>> sizeof(lruvec->lrugen.nr_pages))); >>>>>> >>>>>> And the user-visible impact of underestimated nr_pages in MGLRU was >>>>>> premature OOMs because MGLRU does not try to reclaim memory when nr_pages >>>>>> reaches zero, but there are still more pages. >>>>>> >>>>>> To fix it, make reset_batch_size() check CSS_DYING under RCU before >>>>>> flushing the pending batch. A non-dying memcg keeps the original lruvec >>>>>> stable against RCU-delayed offlining; a dying memcg redirects the deltas >>>>>> to the first non-dying ancestor. >>>>>> >>>>>> Reported-by: Peiyang He >>>>>> Closes: https://lore.kernel.org/all/5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn >>>>>> Fixes: f304652609ea ("mm: vmscan: prepare for reparenting MGLRU folios") >>>>>> Cc: >>>>>> Signed-off-by: Qi Zheng >>>>>> Reviewed-by: Harry Yoo (Oracle) >>>>>> --- >>>>>> Changes in v4: >>>>>> - re-implement lock_batch_lruvec() in a simpler way >>>>>> (suggested by Johannes and Harry) >>>>>> - collect Reviewed-by >>>>>> - rebase onto the next-20260630 >>>>>> >>>>>> Changes in v3: >>>>>> - re-implement lock_batch_lruvec() by checking CSS_DYING under the RCU lock >>>>>> (suggested by Harry) >>>>>> - update the commit message (suggested by Harry) >>>>>> - temporarily drop the previous Reviewed-by tags >>>>>> (since the sync method has changed) >>>>>> - rebase onto the next-20260624 >>>>>> >>>>>> Changes in v2: >>>>>> - update the commit message (pointed by Barry) >>>>>> - collect Reviewed-by >>>>>> >>>>>> mm/vmscan.c | 41 ++++++++++++++++++++++++++++++++++------- >>>>>> 1 file changed, 34 insertions(+), 7 deletions(-) >>>>>> >>>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>>>> index 35c3bb15ae96..ca1e2a870d51 100644 >>>>>> --- a/mm/vmscan.c >>>>>> +++ b/mm/vmscan.c >>>>>> @@ -3262,10 +3262,40 @@ static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio, >>>>>> walk->nr_pages[new_gen][type][zone] += delta; >>>>>> } >>>>>> >>>>>> +#ifdef CONFIG_MEMCG >>>>>> +static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec) >>>>>> +{ >>>>>> + struct pglist_data *pgdat = lruvec_pgdat(lruvec); >>>>>> + struct mem_cgroup *memcg = lruvec_memcg(lruvec); >>>>>> + >>>>>> + rcu_read_lock(); >>>>>> + >>>>>> + /* >>>>>> + * The memcg can be NULL when the memory controller is disabled. >>>>>> + * Otherwise, the caller keeps the memcg owning @lruvec alive. >>>>>> + */ >>>>>> + while (unlikely(memcg && css_is_dying(&memcg->css))) { >>>>>> + memcg = parent_mem_cgroup(memcg); >>>>>> + lruvec = mem_cgroup_lruvec(memcg, pgdat); >>>>>> + } >>>>>> + >>>>>> + spin_lock_irq(&lruvec->lru_lock); >>>>> >>>>> Do we need an rcu_read_unlock() here? >>>> >>>> lruvec_unlock_irq() does that. >>> >>> Yeah, that tripped me up too. And it makes me think Shakeel was right >>> after all: this should live next to the other lruvec_lock() primitives. >>> >>> Sure, MGLRU is the only user, but it's still much easier to understand >>> this if the code sits next to the rest of the API (and the unlock!). >>> >>> lruvec_live_lock_irq()? >> >> But lruvec_lock_irq() grabs the rcu lock too. :( > > Yes, but it's self-explanatory if you put it with those definitions: > > static inline void lruvec_lock_irq(struct lruvec *lruvec) > { > rcu_read_lock(); > spin_lock_irq(&lruvec->lru_lock); > } > > static struct lruvec *lruvec_live_lock_irq(struct lruvec *lruvec) > { > struct mem_cgroup *memcg = lruvec_memcg(lruvec); > > rcu_read_lock(); > while (unlikely(memcg && css_is_dying(&memcg->css))) { > memcg = parent_mem_cgroup(memcg); > lruvec = mem_cgroup_lruvec(memcg, lruvec_pgdat(lruvec)); > } > spin_lock_irq(&lruvec->lru_lock); > } All right, should the implementation for !CONFIG_MEMCG be placed here too? Will send the v5. Thanks, Qi > > static inline void lruvec_unlock_irq(struct lruvec *lruvec) > { > spin_unlock_irq(&lruvec->lru_lock); > rcu_read_unlock(); > } > > etc.