From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-170.mta1.migadu.com (out-170.mta1.migadu.com [95.215.58.170]) (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 448F313D891 for ; Thu, 25 Jun 2026 20:23:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782418998; cv=none; b=SI3GwrfOMGnL05vf+eGjaGe+24nLS/MYt4qJio9CicmNS5j+igcpVPTBYcCyTVLrWY95mvXevUZHniPk9gWIawjnJxveI1cx2sRpHlg/wC2Li9V5pQcK2H+BzGbRls45abZ9Hm753K29nqU9RjJUSJsQ6N39yEsTrN7+F+yBhSE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782418998; c=relaxed/simple; bh=dhkbTkaX1f/Li3P6tkfoUJMb5jqCqJkayXKPr1cpgCQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ct0Y7nBSETvyNMRHMKwY1sLWFVR4BA6AGZXwv+t7khR/Iu6GxFjyU0MJJ3nmAAdDppABscIULZ+Ew36sWywkibMR5EJSbr+WjSnZd224SJdKFSo+xQz52oGM/AuFTuUX0UgnrXuvj+8V9hLJLtsuXoeYSSiAXBts2O6yN8RaTzs= 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=t2yafPs0; arc=none smtp.client-ip=95.215.58.170 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="t2yafPs0" Date: Thu, 25 Jun 2026 13:22:51 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782418983; 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: in-reply-to:in-reply-to:references:references; bh=4666zdLjJLZrpvKtSAgWM48xKMLs0ArCqLFSxNE1+L8=; b=t2yafPs094NOh1WTpNMPZTHY/qli/6qioi0s7PHyfGYLLwRVTq1sRqEpQA07Q1fIM1NRmV C51OX/DEP2PPFJOPcZteAcOzhct1bqnJbnUqVRgwjpViy8GrrkUXRkdPqV/DdX1HOwcwUj HNlmU7yFsgzQO3IBaUfW4U00RtqcGRc= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Shakeel Butt To: Qi Zheng 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 Subject: Re: [PATCH v3] mm: mglru: fix stale batch updates after memcg reparenting Message-ID: References: <20260625151554.55105-1-qi.zheng@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260625151554.55105-1-qi.zheng@linux.dev> X-Migadu-Flow: FLOW_OUT 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. BTW have you checked other places where lruvec_lock_irq is used and if similar kind of situation can happen?