From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-183.mta0.migadu.com (out-183.mta0.migadu.com [91.218.175.183]) (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 16A5F18DF80 for ; Mon, 22 Dec 2025 04:02:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766376148; cv=none; b=VnVrAPxSjhvZ2V+svGGsSsy2pX86en10k376Vwk939IxF00JpOLvTEyk9PZbQwBGYiGGE5QZ4ybb61lBg3WAaNRPWXs2MqjVGyD8EcwtAdUEbaAiiyh1jIkv1L4/nSddOdvKTjwDu/nS0Nj66xyLLAEEA5+yqjScDFPH8r0OMnI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766376148; c=relaxed/simple; bh=2wMOnGongRa/kyIn7SUV+xFRVFlozB+L4nxPmlBfVRA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hOFTuQyCsjseW+W6fZAtwoH/qZzXDEVLzGq8uGAQ63nRp6/kGrDibuQx7K+Sji4/bAODnt+4Ije6hUvbKZ6q/tdmInJh4qFJHgYftGdcSjgW6xrQu9AWMjXni7QgMAx8j50X0211cWH7KWSOZ9sTWR3dUly0ZS2xijGsjdJ0FBU= 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=V6/uE91c; arc=none smtp.client-ip=91.218.175.183 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="V6/uE91c" Message-ID: <59867ffa-7e5d-442f-8e8e-79d5512e03c1@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1766376139; 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=E8FBk6lNZ9dRAmbI0dX/dkHT+ceGlZUbr6C5gAhuy3k=; b=V6/uE91cWY683In/e2wrMi2y7uYHTGMMTqM5DDPH8wgIwEsn0MWLF49vXKTFwmbN/vX4VP vh6AkuxI9K0XZy+np0SqpvJzBANodlUdtPWSfsqXrpMFNdXnexFC9B1Vc+fyhE9Is5DBUT AjEW6lareQy166USAQATDXjHm/cvKHg= Date: Mon, 22 Dec 2025 12:02:11 +0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v2 15/28] mm: memcontrol: prevent memory cgroup release in mem_cgroup_swap_full() To: Shakeel Butt Cc: hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@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: <4dd1fb48ef4367e0932dbe7265d876bd95880808.1765956025.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 On 12/20/25 9:05 AM, Shakeel Butt wrote: > On Wed, Dec 17, 2025 at 03:27:39PM +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 mem_cgroup_swap_full(). >> >> 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 | 10 +++++++--- >> 1 file changed, 7 insertions(+), 3 deletions(-) >> >> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >> index 131f940c03fa0..f2c891c1f49d5 100644 >> --- a/mm/memcontrol.c >> +++ b/mm/memcontrol.c >> @@ -5267,17 +5267,21 @@ bool mem_cgroup_swap_full(struct folio *folio) >> if (do_memsw_account()) >> return false; >> >> - memcg = folio_memcg(folio); >> - if (!memcg) >> + if (!folio_memcg_charged(folio)) >> return false; >> >> + rcu_read_lock(); >> + memcg = folio_memcg(folio); >> for (; !mem_cgroup_is_root(memcg); memcg = parent_mem_cgroup(memcg)) { >> unsigned long usage = page_counter_read(&memcg->swap); >> >> if (usage * 2 >= READ_ONCE(memcg->swap.high) || >> - usage * 2 >= READ_ONCE(memcg->swap.max)) >> + usage * 2 >= READ_ONCE(memcg->swap.max)) { >> + rcu_read_unlock(); >> return true; >> + } >> } >> + rcu_read_unlock(); >> >> return false; >> } > > How about the following? > > > bool mem_cgroup_swap_full(struct folio *folio) > { > struct mem_cgroup *memcg; > + bool ret = false; > > VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); > > if (vm_swap_full()) > return true; > - if (do_memsw_account()) > - return false; > > - if (!folio_memcg_charged(folio)) > - return false; > + if (do_memsw_account() || !folio_memcg_charged(folio)) > + return ret; > > rcu_read_lock(); > memcg = folio_memcg(folio); > @@ -5277,13 +5276,13 @@ bool mem_cgroup_swap_full(struct folio *folio) > > if (usage * 2 >= READ_ONCE(memcg->swap.high) || > usage * 2 >= READ_ONCE(memcg->swap.max)) { > - rcu_read_unlock(); > - return true; > + ret = true; > + break; > } > } > rcu_read_unlock(); > > - return false; > + return ret; > } LGTM, will do. > > > Anyways LGTM. > > Acked-by: Shakeel Butt Thanks!