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 2E5B3D68BE1 for ; Thu, 18 Dec 2025 06:32:12 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 458DC6B0089; Thu, 18 Dec 2025 01:32:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 406636B008A; Thu, 18 Dec 2025 01:32:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 312B36B008C; Thu, 18 Dec 2025 01:32:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 21DBB6B0089 for ; Thu, 18 Dec 2025 01:32:11 -0500 (EST) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id ADB81BDF30 for ; Thu, 18 Dec 2025 06:32:10 +0000 (UTC) X-FDA: 84231622020.27.8CE3D54 Received: from out-177.mta1.migadu.com (out-177.mta1.migadu.com [95.215.58.177]) by imf14.hostedemail.com (Postfix) with ESMTP id CD4BD10000E for ; Thu, 18 Dec 2025 06:32:08 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KFBee5nT; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf14.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.177 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1766039529; a=rsa-sha256; cv=none; b=Qw1OCMlXfl8HEboZPBNFS2RL+3sPfW22qgp/mKkJr7VJRRTIouTMQ9LFb1NxERfhr2ja5c Hkcnvk1ihYi9QVAyXEAFG2PJhfLwWQb3A6sssgyCPeK017CtKVwe7nAJ66mSoFKQ9W8TaM Z0LwbaFN4bLbf/xHLZ1uui6tyM99VMI= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=KFBee5nT; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf14.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.177 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=1766039529; 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=GuMAIMAxghdct3aJXfk8ti9XZUSoxcVspsnX7srcGqs=; b=LTM/HHUyMMgPITQCPq4zoXQutTbfQxcKIEFEXUn6ihLzsKbMJZeP7ix05QOOvX5iw0MkTs 22WPqjiZKVdGD9dCH4QpEz2TCHuHhVQJYPS2E0WcNzb1D8EmqddMIAoMKBCM2f9FctPEyN LPOPI+H+yyXdyqKV82AoIp3idoBwFTE= Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1766039526; 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=GuMAIMAxghdct3aJXfk8ti9XZUSoxcVspsnX7srcGqs=; b=KFBee5nTIhzoI9YEZNoVUIkAkpAX+95cyo5ZbyznMbVg80cFiduvqe3iOLSyfH1F7yrANX BC9xI2JhDTlys1R/SarHKY2E12ETA0eO9YYcKBcmlJ6QozfDzcVEvwLaxCSkXX31/2xxTL gfQN/eSKa8XVV4ZxKZwfH7DlY53ijd8= Date: Thu, 18 Dec 2025 14:31:51 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v2 08/28] mm: memcontrol: prevent memory cgroup release in get_mem_cgroup_from_folio() To: Johannes Weiner Cc: hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, david@kernel.org, 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, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng References: <29e5c116de15e55be082a544e3f24d8ddb6b3476.1765956025.git.zhengqi.arch@bytedance.com> 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 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: CD4BD10000E X-Stat-Signature: 5ptycgepewescqck6r3roqc438yskdj3 X-Rspam-User: X-HE-Tag: 1766039528-928004 X-HE-Meta: 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 +kMfYTIy fiSNZP3uPT159ukHrccryfCQXOXHI7RbFZcwOrTYapOavrnyv5+i97EePbqTdKOBscxlxjH6Fmz4OqBoNJ7NhtRtM0CeTf6iqXP/vktRKkyuLnriTL0PRU/bW/U0MoGjzJvSRpEBqH0ivgQvsHDOImxiWsLiTkZU9r55W4o3ikLrEQ4cLMp5Qkclkbc7iCKhU1QbZQjxmzyNq4lrzAHTz6mFHNuBZoO16s0zxqTpJBy4R432vjMEWMzU8I3h2yrfbwM2/NCo9MtJI7Hy3ihYSKxxwPaR+0FjJgGHKmWbtDvhiE5w= 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 5:45 AM, Johannes Weiner wrote: > On Wed, Dec 17, 2025 at 03:27:32PM +0800, 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 get_mem_cgroup_from_folio(). >> >> 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/memcontrol.c | 11 ++++++++--- >> 1 file changed, 8 insertions(+), 3 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 21b5aad34cae7..431b3154c70c5 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -973,14 +973,19 @@ struct mem_cgroup *get_mem_cgroup_from_current(void) >> */ >> struct mem_cgroup *get_mem_cgroup_from_folio(struct folio *folio) >> { >> - struct mem_cgroup *memcg = folio_memcg(folio); >> + struct mem_cgroup *memcg; >> >> if (mem_cgroup_disabled()) >> return NULL; >> >> + if (!folio_memcg_charged(folio)) >> + return root_mem_cgroup; >> + >> rcu_read_lock(); >> - if (!memcg || WARN_ON_ONCE(!css_tryget(&memcg->css))) >> - memcg = root_mem_cgroup; >> +retry: >> + memcg = folio_memcg(folio); >> + if (unlikely(!css_tryget(&memcg->css))) >> + goto retry; > > So starting in patch 27, the tryget can fail if the memcg is offlined, > and the folio's objcg is reparented concurrently. We'll retry until we > find a memcg that isn't dead yet. There's always root_mem_cgroup. > > It makes sense, but a loop like this begs the question of how it is > bounded. I pieced it together looking ahead. Since this is a small > diff, it would be nicer to fold it into 27. I didn't see anything in > between depending on it, but correct me if I'm wrong. Right, will fold it into #27 in the next version. > > Minor style preference: > > /* Comment explaining the above */ > do { > memcg = folio_memcg(folio); > } while (!css_tryget(&memcg->css)); OK, will do. Thanks, Qi