From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (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 303C7332623 for ; Fri, 26 Jun 2026 02:39:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782441571; cv=none; b=JDGRXbvhvZTMII6R4fYLu2jdhmuj3++NuL98FYCvxA0Kd8xpSCt23NRG8K7bUYm7foYsRXbFURirN51N7lA+BLS+BubZ0nKlS67PIK/yLjEH18q0WTPaAFvFSRztHDXVs3BXRKIProZLih3VZDAc8949lKYfCY70ZexEBB7PVs0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782441571; c=relaxed/simple; bh=8E8GaubErZXXm9BNp6qLG1+xEyXvonWSsfvk/hNcy8U=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cTsiMGIyv8W0mf/LJakU9wtmeWleAOM98hYUSveXowW6euu30X3fVKhvza5//zSLpQp+oiiI3omtCGPx64sVUlLSoZVaDrA/Gm1fANnTr4LzEEcDc8XCXMU8QQsAzs4Ae9fof1cjxF575wENU+4XryVDCMUPi9Xt8VV5zwt4Dpk= 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=HlxqWPhj; arc=none smtp.client-ip=91.218.175.188 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="HlxqWPhj" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782441557; 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=eMiBjpoG5x/PF8SzAf5XymHhBXZlwVkuA+guTc6Tz+s=; b=HlxqWPhjhC0j9hY/ieFKCrb9rfUDoIAlwoC+Sk8MOyqCqBiTsnN35cs89wF5SYH1TEWLOi qzU92R1k5+LncMjCk6o3/6qcDbYVn5k6wg7D8VSJCiDmMAkD8vPvVrqWPIfU5iR2Bx+jJI 0er9sGgDMCZzJFFnjaiRH1MvAimy1aA= Date: Fri, 26 Jun 2026 10:39:00 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3] mm: mglru: fix stale batch updates after memcg reparenting To: Shakeel Butt Cc: akpm@linux-foundation.org, david@kernel.org, kasong@tencent.com, baohua@kernel.org, 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: <20260625151554.55105-1-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: 7bit X-Migadu-Flow: FLOW_OUT Hi Shakeel, On 6/26/26 4:22 AM, Shakeel Butt wrote: > On Thu, Jun 25, 2026 at 11:15:54PM +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 >> --- >> 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 | 45 ++++++++++++++++++++++++++++++++++++++------- >> 1 file changed, 38 insertions(+), 7 deletions(-) >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 35c3bb15ae96..1ec8c23c72b9 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -3262,10 +3262,44 @@ 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) > > This is memcg specific function, move this function next to similar functions > like lruvec_lock_irq. Also put irq in the name. Currently, the lock_batch_lruvec() is only used by reset_batch_size(). Are you intend to make it a common function for use in other places? Perhaps we could defer making it generic until we actually have a second user. Since this is just a fix, keeping it self-contained within vmscan.c might be more compact for now. ;) > > BTW have you checked other places where lruvec_lock_irq is used and if similar > kind of situation can happen? I just checked and found no such callers. Thanks, Qi >