From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) (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 56D321C3F31 for ; Tue, 23 Jun 2026 01:58:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782179904; cv=none; b=RIY4LnKZuRdicm0AFnhKn0lCESPqlmZiUG5gQgJAj9Kt8/R+dHg6c+5TrRhNNSGllSEdsQS319wPAT0PFDnJY5L38IIAyQxRLvhaj6Z23U6THu3M2KnD6fbbiHPE3asX8vcNZS3wKC0e5oRasP0VEN7JkqMt09M73M0Xt2Ufu9Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782179904; c=relaxed/simple; bh=xHgdRTGgN9tAEW0PV0VYjqTIedXY7cD35mOQAD1AFCc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=a8r2cpuCoSvqSNxe3Ig65ingH01yRQcidzQ+X3QoN9Rvk6PRCkLREyNeJ/4q3TIvoO90dX9ta0G5H+a6HgWm0SxykPJuRSZ7fws93NzG1uXHu2Q5vQuriG7nOVye8b1np0czrXO42Q6Y+4FFEnNaUCqP+jNHNHmcKiBzxrw+L0A= 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=nVU9jaYf; arc=none smtp.client-ip=95.215.58.176 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="nVU9jaYf" Message-ID: <19710ee5-8e1c-4b13-812b-4b03ca34260d@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782179900; 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=vB3i4adRYFyfJdlhTLJBnXcY+A/xZ4fOjEV+12UNO30=; b=nVU9jaYfAdR3Kg5OdpQ8NdQY8lYzn36Pa3qWCV2kxePiO7/Kl01rM+fWGrhc/stxijbqL+ qCXr20ySoNM4fnI20ayBDDhONqwbZZhvZHnPGSp2kMbEJoGjxoGqwfEvixF1W6C43KNP6F +W/8gm0/04WNK50L6P01p7mNDgll41Y= Date: Tue, 23 Jun 2026 09:57:47 +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: mglru: fix stale batch updates after memcg reparenting To: Barry Song Cc: akpm@linux-foundation.org, david@kernel.org, kasong@tencent.com, shakeel.butt@linux.dev, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, harry@kernel.org, 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: <5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn> <20260622073703.79258-1-qi.zheng@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: 8bit X-Migadu-Flow: FLOW_OUT Hi Barry, On 6/23/26 6:52 AM, Barry Song wrote: > On Mon, Jun 22, 2026 at 3:38 PM 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 can trigger the following warning: >> >> WARNING: mm/vmscan.c:5867 at lru_gen_exit_memcg+0x26f/0x300 >> RIP: 0010:lru_gen_exit_memcg+0x26f/0x300 mm/vmscan.c:5867 > > I can't find 5867; instead, I can find 5828: > > VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, > sizeof(lruvec->lrugen.nr_pages))); > > Is this the warning? Yes, I just copy-pasted the warning log from Peiyang's report. Maybe the description should be changed to: 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))); > >> Call Trace: >> >> mem_cgroup_free mm/memcontrol.c:3972 [inline] >> mem_cgroup_css_free+0x76/0xb0 mm/memcontrol.c:4241 >> css_free_rwork_fn+0x125/0x1260 kernel/cgroup/cgroup.c:5575 >> process_one_work+0xa0d/0x1c30 kernel/workqueue.c:3314 >> process_scheduled_works kernel/workqueue.c:3397 [inline] >> worker_thread+0x645/0xe80 kernel/workqueue.c:3478 >> kthread+0x367/0x480 kernel/kthread.c:436 >> ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 >> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 >> >> >> To fix it, add lrugen->reparented to remember the new owner of a >> reparented lruvec, and make reset_batch_size() charge pending deltas to >> that owner. >> >> 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 > > Looks reasonable to me. > Reviewed-by: Barry Song Thanks!