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From: Shakeel Butt To: Qi Zheng Cc: Harry Yoo , hannes@cmpxchg.org, hughd@google.com, mhocko@suse.com, roman.gushchin@linux.dev, muchun.song@linux.dev, david@redhat.com, lorenzo.stoakes@oracle.com, ziy@nvidia.com, imran.f.khan@oracle.com, kamalesh.babulal@oracle.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Muchun Song , Qi Zheng , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , linux-rt-devel@lists.linux.dev Subject: Re: [PATCH v1 04/26] mm: vmscan: refactor move_folios_to_lru() Message-ID: <646pwrc7sxan6wlwndjyu7upx32fkd7bv5vqlut3tjt65eeyby@23efyxvpg2nx> References: <97ea4728568459f501ddcab6c378c29064630bb9.1761658310.git.zhengqi.arch@bytedance.com> <366385a3-ed0e-440b-a08b-9cf14165ee8f@linux.dev> <2a68bddf-e6e6-4960-b5bc-1a39d747ea9b@linux.dev> <8d6655f8-2756-45bb-85c1-223c3a5e656c@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8d6655f8-2756-45bb-85c1-223c3a5e656c@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 400E420002 X-Stat-Signature: qymywyy47g5md637jhii68boke8rgh5q X-Rspam-User: X-HE-Tag: 1762831055-547553 X-HE-Meta: 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 2reQ7/al 2oGpXd6N6ItfNXdb5704GCJFaAptrgimq6p+hPtKf47UG7GhzEWOzE/ksppCAn87L9jO2mumYYMldq6gV3Ep+FZALqbDNmNJZcBsDph3YEbebQyv2c6ef8POp58FuJeYgLkZ4XB+pZ+GMCm/LxgHtDheSejCh7wf2j8cq0c7FesgyG6yqZntTYgpmxuKFEK1ja0Y6sMh6i+3jfjvzdxNy3ppynkC2pncIfW8NkQgKaEcUMxdX7mOuVpYxqCePd39tEofT 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, Nov 11, 2025 at 11:04:09AM +0800, Qi Zheng wrote: > > On 11/11/25 12:47 AM, Shakeel Butt wrote: > > On Mon, Nov 10, 2025 at 02:43:21PM +0900, Harry Yoo wrote: > > > On Mon, Nov 10, 2025 at 12:30:06PM +0800, Qi Zheng wrote: > > > > > Maybe we could make it safe against re-entrant IRQ handlers by using > > > > > read-modify-write operations? > > > > > > > > Isn't it because of the RMW operation that we need to use IRQ to > > > > guarantee atomicity? Or have I misunderstood something? > > > > > > I meant using atomic operations instead of disabling IRQs, like, by > > > using this_cpu_add() or cmpxchg() instead. > > > > We already have mod_node_page_state() which is safe from IRQs and is > > optimized to not disable IRQs for archs with HAVE_CMPXCHG_LOCAL which > > includes x86 and arm64. > > However, in the !CONFIG_HAVE_CMPXCHG_LOCAL case, mod_node_page_state() > still calls local_irq_save(). Is this feasible in the PREEMPT_RT kernel? > Yes we can disable irqs on PREEMPT_RT but it is usually frown upon and it is usually requested to do so only for short window. However if someone running PREEMPT_RT on an arch without HAVE_CMPXCHG_LOCAL and has issues with mod_node_page_state() then they can solve it then. I don't think we need to fix that now.