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Wed, 17 Dec 2025 14:08:57 -0800 (PST) Date: Wed, 17 Dec 2025 17:08:53 -0500 From: Johannes Weiner To: Qi Zheng 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 Subject: Re: [PATCH v2 10/28] writeback: prevent memory cgroup release in writeback module Message-ID: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Dec 17, 2025 at 03:27:34PM +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 function get_mem_cgroup_css_from_folio() > and the rcu read lock are employed to safeguard against the release > of the memory cgroup. > > 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 Looks sane to me. The roo_mem_cgroup handling in get_mem_cgroup_css_from_folio() is unusual - usually we do NULL for mem_cgroup_disabled(). But that's a quirk you're inheriting from the existing writeback code. Acked-by: Johannes Weiner