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Goncalves" , Andrew Morton , Mel Gorman , Michal Hocko , Thomas Gleixner Subject: Re: [PATCH] mm/page_alloc: Use write_seqlock_irqsave() instead write_seqlock() + local_irq_save(). Message-ID: <20230623124416.M8fKvITC@linutronix.de> References: <01031ffe-c81f-9cec-76fb-e70d548429cf@I-love.SAKURA.ne.jp> <8b6d3f39-c573-ca2b-957b-8c48c2fa68ad@I-love.SAKURA.ne.jp> <20230623094544.RcLNdg6H@linutronix.de> <20230623101111.7tuAg5p5@linutronix.de> <115cf90c-5bc5-d4b0-6489-d1ee5735194a@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <115cf90c-5bc5-d4b0-6489-d1ee5735194a@I-love.SAKURA.ne.jp> X-Rspamd-Queue-Id: 4A52040022 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: gh4h9oo6igkjm5hmpmc9gqztyhcjycwx X-HE-Tag: 1687524259-912192 X-HE-Meta: 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 SolIN5LW MvXwSMydoRSvLb/8k2JQoaQOLzirIn7M0kvGN0S4QZBhwYZgWBAgFTLYGhrJzH9/zw8qmtJFQ+1457rR4VzV007kilNbcO8QI7LurjBPSEm6hCLo6qs+sWDYfwXRlLAUR3J42+yHLww7yHsk= 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: On 2023-06-23 19:36:55 [+0900], Tetsuo Handa wrote: > /* > * Zonelists may change due to hotplug during allocation. Detect when zonelists > * have been rebuilt so allocation retries. Reader side does not lock and > * retries the allocation if zonelist changes. Writer side is protected by the > * embedded spin_lock. > */ > > is not accurate. Something like below? > > If !RT, reader side does not lock and retries the allocation if zonelist changes. > If RT, reader side grabs and releases the embedded spin_lock in order to wait > for zonelist change operations to complete. I wouldn't sprinkle it around the code. It is implementation specific for PREEMPT_RT and documentation wise it would belong to Documentation/locking/seqlock.rst I don't think extra knowledge benefits the code. If this piece if information is needed I would suggest to include it to the original documentation for seqlock. > Hmm, I feel worried that kmalloc(GFP_ATOMIC) from hard IRQ context > might sleep if RT... Relax and don't worry. PREEMPT_RT does not allow (or has afaik) memory allocations from hard IRQ context (or preempt-disable sections). Sebastian