From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-172.mta1.migadu.com (out-172.mta1.migadu.com [95.215.58.172]) (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 B638F33066A for ; Thu, 18 Dec 2025 09:36:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766050588; cv=none; b=FHPk7ZH6yyDXnI2LiUFEbAeBc3xeRusOLSqw7IHv93pNruEJqlqcKXergguwlPMfCd8jyoezVwMrllIN6htfmaYaUp6t20ud+UBCniCqCsFped9lrj0Gg1Z3mMM8+GeEV+bMClpUThnTe8Xw3thW5EzF9oQB4zisMVvOpNhYOXE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766050588; c=relaxed/simple; bh=ua1YjQwoGUxl1srrWu+EopWerUHaXBHmdI6tAD/TOWs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EymQ7TNgDFCuUGXIItuSys9FL/qUqTj7u/MwzqqIVFigk2lQwgeD4puQ4PIwBUbHGLXgENDlKU1lrTGWDQxSOIly7VKrjCcddewgsLDFNfxWHW/F9FGCwqiVJqhAltNlHb8ORAI+g0uJ8T4zk5mydsKY1ddCdYnqQ9omZ/I/szY= 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=qF7ex1vz; arc=none smtp.client-ip=95.215.58.172 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="qF7ex1vz" Message-ID: <02c3be32-4826-408d-8b96-1db51dcababf@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1766050574; 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=WXEVgSDfFQRZmqw91gtvqofxkpPFsKG1MF14J7844dQ=; b=qF7ex1vzVKMpqENmGb0AMh9twBFnr9nMf5mpXKR5++Gd6nWWWaAURqJCzsViZnil6yFo1B HOS+UAqUSEyN7ZMBZCH4sigL5pZfQDcy/5KZboawYghYgp/TmmRXe2/bnD2YFYp5F/RRRW EwT/AgFmuhPpXUU2TWiq2WzRFhdOpGY= Date: Thu, 18 Dec 2025 17:36:00 +0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: <3a6ab69e-a2cc-4c61-9de1-9b0958c72dda@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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()? > > Something like "start / end" semantics. > > -- > Cheers > > David