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Tue, 09 Sep 2025 07:45:32 -0700 (PDT) Date: Tue, 9 Sep 2025 15:45:31 +0100 From: Johannes Weiner To: Michal Hocko Cc: cuishiwei , akpm@linux-foundation.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, david@redhat.com, zhengqi.arch@bytedance.com, shakeel.butt@linux.dev, lorenzo.stoakes@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] disable demotion during memory reclamation Message-ID: <20250909144531.GA1474@cmpxchg.org> References: <20250909012141.1467-1-cuishw@inspur.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 9373610000A X-Stat-Signature: yhgmg46ez6h8e1o9wtdi1a85koo913ti X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1757429134-931215 X-HE-Meta: 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 wa6r8JpB SOeyrH7DFj+c1uI9cfLyVhW5lUVom4g8K89AM+nL2jRU7tXzx6YYLqeuVJk/bVyBUrTFajvkTn3RM1xDBsvlfWwfpUw== 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 Tue, Sep 09, 2025 at 09:40:51AM +0200, Michal Hocko wrote: > On Tue 09-09-25 09:21:41, cuishiwei wrote: > > When a memory cgroup exceeds its memory limit, the system reclaims > > its cold memory.However, if /sys/kernel/mm/numa/demotion_enabled is > > set to 1, memory on fast memory nodes will also be demoted to slow > > memory nodes. > > > > This demotion contradicts the goal of reclaiming cold memory within > > the memcg.At this point, demoting cold memory from fast to slow nodes > > is pointless;it doesn't reduce the memcg's memory usage. Therefore, > > we should set no_demotion when reclaiming memory in a memcg. > > We have discussed this in the past and it is my recollection that we > have concluded that demotion is a part of proper aging and therefore it > should be done during the limit reclaim. Yes, thanks. This is intentional. Please see 3f1509c57b1b ("Revert "mm/vmscan: never demote for memcg reclaim"") for more details.