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 8768ED6ACFB for ; Thu, 18 Dec 2025 13:01:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DFAD96B0089; Thu, 18 Dec 2025 08:01:18 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D7A9F6B008A; Thu, 18 Dec 2025 08:01:18 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C942F6B008C; Thu, 18 Dec 2025 08:01:18 -0500 (EST) 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 B2F7F6B0089 for ; Thu, 18 Dec 2025 08:01:18 -0500 (EST) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 797B4C0155 for ; Thu, 18 Dec 2025 13:01:18 +0000 (UTC) X-FDA: 84232602636.24.BB96245 Received: from out-172.mta0.migadu.com (out-172.mta0.migadu.com [91.218.175.172]) by imf07.hostedemail.com (Postfix) with ESMTP id 7BBEB40005 for ; Thu, 18 Dec 2025 13:01:16 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=SEdTet5h; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf07.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.172 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1766062876; a=rsa-sha256; cv=none; b=ouMEqj1xIenjCBYX2indJWzGBG7eSWhbgk3Hna6z3ulQkH7GDZ8FE4DZlTfHkhnSa80Qf7 LLm/2c64pj2C96hILbJYiqTjB2A37QpjhUGQ0tvSS1oBGHej3nXhnr7TRo1TV8JlxFeFYf PEziSVzi+KqIAnA84AWJuynpwDBl0Lo= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=SEdTet5h; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf07.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.172 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=1766062876; 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=3fhAxNBkZvzSd2fHbQh2tDrHQZkQx5sWn3l+p/o/E8Q=; b=1/Jt1X557eyyqgDXJB+7aR1XxnH5jIXKPF5sY5MiYhlP4wf34bx4pxZfe61MSeMiNlTi4X CY1u10Rxq0PpauTIGooH9HPQa4gflR39V7VdANMmcpIgv7E7z+v73V3cBnfDEPJLhNCBAP AgKD/0u5kfZwCcg7APB/AVuIOSad2CQ= Message-ID: <3c32d80a-ba0e-4ed2-87ae-fb80fc3374f7@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1766062869; 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=3fhAxNBkZvzSd2fHbQh2tDrHQZkQx5sWn3l+p/o/E8Q=; b=SEdTet5hPnFsPgIW/3Ked4lMxNyGaR8bXywSfUqJ8il0v4bSoUw+RR4+SYdKpVn0eDCKe1 vGGTrfKrIRypODY1FnZzLP6m3+ob7vnBehCZpZcY2GWy0V8nSWYIROMhcJB1zl0N5JNZ6H W5k9IvQQ0QkpOnvStZGedD0aFZuvlhw= Date: Thu, 18 Dec 2025 21:00:53 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v2 13/28] mm: migrate: prevent memory cgroup release in folio_migrate_mapping() To: "David Hildenbrand (Red Hat)" , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, lorenzo.stoakes@oracle.com, ziy@nvidia.com, harry.yoo@oracle.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, chenridong@huaweicloud.com, mkoutny@suse.com, akpm@linux-foundation.org, hamzamahfooz@linux.microsoft.com, apais@linux.microsoft.com, lance.yang@linux.dev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng References: <1554459c705a46324b83799ede617b670b9e22fb.1765956025.git.zhengqi.arch@bytedance.com> <3a6ab69e-a2cc-4c61-9de1-9b0958c72dda@kernel.org> <02c3be32-4826-408d-8b96-1db51dcababf@linux.dev> <4effa243-bae3-45e4-8662-dca86a7e5d12@linux.dev> <11a60eba-3447-47de-9d59-af5842f5dc5e@kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: <11a60eba-3447-47de-9d59-af5842f5dc5e@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7BBEB40005 X-Stat-Signature: cth4a4wmw5ryrffi3qbhg7r7f8c5q333 X-HE-Tag: 1766062876-395195 X-HE-Meta: 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 NzCALMW6 +gbH8EhwhnyEbRuumuRn3FoW9qq5RUD68Kw8ljE4tVacjcag+e5j3aMHgZx0mIapHfeu8OFUxlPhC9Yjlu6mzV1BuxtjTbIY8/oNXCYyqJ0wuNgJLu6KTQNX4OBhCTgglLOReIobY0uwmX9RbaQsIUP7MLxF82168MLsyFf84lHfvu637NYtcx+7Axvf7Sx6kjG2XjDA4MjfFqhHD/BeseVoeVfTsWyNN81972miJaiVxgLdX8CFiCCVisCtJA7B1grYEOTxE2ZDol1fRRB7X7xs6FLGha4fGIosqC67TJExQmv10HIgpaqbErwI/+tmuhbi3ldYyF6Ji4+o= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/18/25 7:56 PM, David Hildenbrand (Red Hat) wrote: > On 12/18/25 12:40, Qi Zheng wrote: >> >> >> On 12/18/25 5:43 PM, David Hildenbrand (Red Hat) wrote: >>> On 12/18/25 10:36, Qi Zheng wrote: >>>> >>>> >>>> On 12/18/25 5:09 PM, David Hildenbrand (Red Hat) wrote: >>>>> On 12/17/25 08:27, Qi Zheng wrote: >>>>>> From: Muchun Song >>>>>> >>>>>> In the near future, a folio will no longer pin its corresponding >>>>>> memory cgroup. To ensure safety, it will only be appropriate to >>>>>> hold the rcu read lock or acquire a reference to the memory cgroup >>>>>> returned by folio_memcg(), thereby preventing it from being released. >>>>>> >>>>>> In the current patch, the rcu read lock is employed to safeguard >>>>>> against the release of the memory cgroup in folio_migrate_mapping(). >>>>> >>>>> We usually avoid talking about "patches". >>>> >>>> Got it. >>>> >>>>> >>>>> In __folio_migrate_mapping(), the rcu read lock ... >>>> >>>> Will do. >>>> >>>>> >>>>>> >>>>>> This serves as a preparatory measure for the reparenting of the >>>>>> LRU pages. >>>>>> >>>>>> Signed-off-by: Muchun Song >>>>>> Signed-off-by: Qi Zheng >>>>>> Reviewed-by: Harry Yoo >>>>>> --- >>>>>>     mm/migrate.c | 2 ++ >>>>>>     1 file changed, 2 insertions(+) >>>>>> >>>>>> diff --git a/mm/migrate.c b/mm/migrate.c >>>>>> index 5169f9717f606..8bcd588c083ca 100644 >>>>>> --- a/mm/migrate.c >>>>>> +++ b/mm/migrate.c >>>>>> @@ -671,6 +671,7 @@ static int __folio_migrate_mapping(struct >>>>>> address_space *mapping, >>>>>>             struct lruvec *old_lruvec, *new_lruvec; >>>>>>             struct mem_cgroup *memcg; >>>>>> +        rcu_read_lock(); >>>>>>             memcg = folio_memcg(folio); >>>>> >>>>> In general, LGTM >>>>> >>>>> I wonder, though, whether we should embed that in the ABI. >>>>> >>>>> Like "lock RCU and get the memcg" in one operation, to the "return >>>>> memcg >>>>> and unock rcu" in another operation. >>>> >>>> Do you mean adding a helper function like get_mem_cgroup_from_folio()? >>> >>> Right, something like >>> >>> memcg = folio_memcg_begin(folio); >>> folio_memcg_end(memcg); >> >> For some longer or might-sleep critical sections (such as those pointed >> by Johannes), perhaps it can be defined like this: >> >> struct mem_cgroup *folio_memcg_begin(struct folio *folio) >> { >>     return get_mem_cgroup_from_folio(folio); >> } >> >> void folio_memcg_end(struct mem_cgroup *memcg) >> { >>     mem_cgroup_put(memcg); >> } >> >> But for some short critical sections, using RCU lock directly might >> be the most convention option? >> > > Then put the rcu read locking in there instead? So for some longer or might-sleep critical sections, using: memcg = folio_memcg_begin(folio); do_some_thing(memcg); folio_memcg_end(folio); for some short critical sections, using: rcu_read_lock(); memcg = folio_memcg(folio); do_some_thing(memcg); rcu_read_unlock(); Right? >