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From: Shakeel Butt To: Qi Zheng 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, yosry.ahmed@linux.dev, 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 v3 08/30] mm: memcontrol: prevent memory cgroup release in get_mem_cgroup_from_folio() Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 164B5120010 X-Rspam-User: X-Stat-Signature: rbxjcp5a85axih96wzwk4homra9o5ddk X-HE-Tag: 1768680078-753982 X-HE-Meta: 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 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 Wed, Jan 14, 2026 at 07:32:35PM +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. This patch is adding a retry loop as css_tryget() on folio_memcg() can fail because after reparenting functionality the folio no longer holds down the memcg. Please clarify this reasoning in the commit. With that: Acked-by: Shakeel Butt