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From: Shakeel Butt To: Sebastian Andrzej Siewior Cc: Harry Yoo , Qi Zheng , 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 , 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: References: <366385a3-ed0e-440b-a08b-9cf14165ee8f@linux.dev> <2a68bddf-e6e6-4960-b5bc-1a39d747ea9b@linux.dev> <8d6655f8-2756-45bb-85c1-223c3a5e656c@linux.dev> <20251111084900.babaOj0w@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251111084900.babaOj0w@linutronix.de> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: gt81gw1egy6huima596eqajimy39bhmw X-Rspam-User: X-Rspamd-Queue-Id: 4AB7820003 X-Rspamd-Server: rspam10 X-HE-Tag: 1762879466-893283 X-HE-Meta: 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 4MjhMZkJ knDTdTXLdWpnx/FTHA5ZG2NpgxAfimZl/FpobH/F32bqbocJAMxSRcgezxgd3e6td7d8cSflY8nSbNT2zhmS3VicimD7dNT+5foUqq5gKWgn5KxMEyMuOqqX1rZst88p+uCXkd9FNgWMMkvjBo/KC6jQ3J18PHdD9xKl9XJ4JY1XaWheqLo33GJCWBa8Foo9/LKe+Y3BRryCn5erPnLxp99PGTFO+YWyLsHzys7UpfI5E+kTqBT5NHVga65Xq+jiVVUxB 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 09:49:00AM +0100, Sebastian Andrzej Siewior wrote: > On 2025-11-11 12:16:43 [+0900], Harry Yoo wrote: > > > 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? > > > > Hmm I was going to say it's necessary, but AFAICT we don't allocate > > or free memory in hardirq context on PREEMPT_RT (that's the policy) > > and so I'd say it's not necessary to disable IRQs. > > > > Sounds like we still want to disable IRQs only on !PREEMPT_RT on > > such architectures? > > > > Not sure how seriously do PREEMPT_RT folks care about architectures > > without HAVE_CMPXCHG_LOCAL. (riscv and loongarch have ARCH_SUPPORTS_RT > > but doesn't have HAVE_CMPXCHG_LOCAL). > > We take things seriously and you shouldn't make assumption based on > implementation. Either the API can be used as such or not. > In case of mod_node_page_state(), the non-IRQ off version > (__mod_node_page_state()) has a preempt_disable_nested() to ensure > atomic update on PREEMPT_RT without disabling interrupts. > Harry is talking about mod_node_page_state() on !CONFIG_HAVE_CMPXCHG_LOCAL which is disabling irqs. void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, long delta) { unsigned long flags; local_irq_save(flags); __mod_node_page_state(pgdat, item, delta); local_irq_restore(flags); } Is PREEMPT_RT fine with this?