From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E03E131E857; Fri, 26 Jun 2026 07:15:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782458135; cv=none; b=tdcVmU/SoIcgcMLyjIBfmQj3bls+yyLl4ki3XtkGLJaG1knJtyDzI0hSXSlHcWwtO2uQeJ2Y6VzjcXueLQxVAK5oDHQuqtpcihg38TQ5RfQGVgmxVt4MVdkceOUrlVeMsvkCnj9qpM4kQeuqnq+ZJzsnCm0sOwATQtHL6Ba0Hss= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782458135; c=relaxed/simple; bh=9RR1bBMY56xbcT+FAcSx+2o3Qwm6rpAKLhB42TGTEHI=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=f4qE7ljkwzaeRRRT3+VZ0t7E3NU6rM2dDCgMjrKuXrr4d1pDVBECG8wV0ehiccaLf1i8OWj+myC9TeEMsvzR7lmX3hJfRMTsWXmGJzZCAF34DcHzw60jUpc9QbpJPZxbceAQVEyWpYDYDQK0Zgj4DSRL+hFdTHFNQxNH14CKnI0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OxwOaYpa; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OxwOaYpa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B840A1F000E9; Fri, 26 Jun 2026 07:15:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782458133; bh=3lVxdm0Ep0/M2ZYIKTC77sSAb+8Ja64CITv1+WKNFCo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=OxwOaYpaqmr2aOcT0SoHP1REiLiNj80JROVsNPvrfmy/4xobxnTZ8DFNS8aLhzsG2 pc1JYInzhAEN2BaPLK5IIiAOHveUeNvdS1h9ZGykqqnp5ZGjRF3zukUH5/xWpDaG4a RLnkTDu6Q+3/Z+sAuJ4XlXT4mNqSWDTTOVDsTtQi8inuy+EB/yIT2FcP2ihzw3bZqr j+iVV5RthEeDUHnj51btEokTNkIRCnngT+INPOu+UcePKVCbVPX4EZKw+Tlt7lv3My 3mwPy1OWlmkE3FxK8W0FsHXg9gLrC5vSd88rLK6Wzytl3VcjKiIyKvITr5gkqr/kZ9 26sUDDbQD9wjA== Message-ID: Date: Fri, 26 Jun 2026 16:15:24 +0900 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm: mglru: fix stale batch updates after memcg reparenting To: Qi Zheng , 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, hannes@cmpxchg.org, muchun.song@linux.dev, peiyang_he@smail.nju.edu.cn, mhocko@kernel.org, roman.gushchin@linux.dev, ljs@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng , stable@vger.kernel.org References: <20260625151554.55105-1-qi.zheng@linux.dev> Content-Language: en-US From: Harry Yoo In-Reply-To: <20260625151554.55105-1-qi.zheng@linux.dev> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------m7QUOiwKcAfVY02vm0zfaXUG" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --------------m7QUOiwKcAfVY02vm0zfaXUG Content-Type: multipart/mixed; boundary="------------5KW8ae2yJZ4W4qD8pteHlVMf"; protected-headers="v1" From: Harry Yoo To: Qi Zheng , 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, hannes@cmpxchg.org, muchun.song@linux.dev, peiyang_he@smail.nju.edu.cn, mhocko@kernel.org, roman.gushchin@linux.dev, ljs@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng , stable@vger.kernel.org Message-ID: Subject: Re: [PATCH v3] mm: mglru: fix stale batch updates after memcg reparenting References: <20260625151554.55105-1-qi.zheng@linux.dev> In-Reply-To: <20260625151554.55105-1-qi.zheng@linux.dev> --------------5KW8ae2yJZ4W4qD8pteHlVMf Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 6/26/26 12:15 AM, Qi Zheng wrote: > From: Qi Zheng >=20 > The mglru page table walker batches per-generation size deltas in > walk->nr_pages while walking page tables without holding the lruvec loc= k. > The reset_batch_size() later folds those deltas into walk->lruvec under= > the lruvec lock. >=20 > The page table walker can run concurrently with the memcg reparenting p= ath > as follows: >=20 > CPU0 CPU1 > =3D=3D=3D=3D =3D=3D=3D=3D >=20 > walk_mm > --> walk_page_range > --> update_batch_size > --> walk->nr_pages +=3D delta >=20 > mem_cgroup_css_offline > --> memcg_reparent_objcgs > --> lock lruvec > lru_gen_reparent_memcg > --> reparent child folios to pare= nt > unlock lruvec >=20 > lock lruvec > reset_batch_size > --> child lrugen->nr_pages +=3D delta >=20 > This will trigger the following warning in lru_gen_exit_memcg(): >=20 > VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, > sizeof(lruvec->lrugen.nr_pages))); >=20 > And the user-visible impact of underestimated nr_pages in MGLRU was > premature OOMs because MGLRU does not try to reclaim memory when nr_pag= es > reaches zero, but there are still more pages. >=20 > 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 delta= s > to the first non-dying ancestor. >=20 > 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 > --- besides some nits mentioned elsewhere in the thread, the approach looks good to me, so: Reviewed-by: Harry Yoo (Oracle) --=20 Cheers, Harry / Hyeonggon --------------5KW8ae2yJZ4W4qD8pteHlVMf-- --------------m7QUOiwKcAfVY02vm0zfaXUG Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature.asc" -----BEGIN PGP SIGNATURE----- iHUEARYKAB0WIQQQ1ub6gR5ogjaKRmOGXBN6rc5S1gUCaj4nDAAKCRCGXBN6rc5S 1vJdAP41DQ/Adn/NHl8DrlVUlhHpdYGNd+BlOc6FRwocVOTrGQEA/zSmKeZqWesI TcJfcwrQQoZKB/v7BJGNTnJRLM7YEg0= =xY2b -----END PGP SIGNATURE----- --------------m7QUOiwKcAfVY02vm0zfaXUG--