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bh=hjmsQNbabVrHMjgajgEZibUL+efg9RjKcTRD2S+ysQ8=; b=f2HB/A/hb6zPD+MvHy/KC6OdmWpC1V68JL0jW4qNfv0jLBEggJ0szbe/6OorO2hbDxG684 ArYQRJhVOGOBDvhNEI2ERthAEZnlBT2HjBfL/kf0+8KhcCPVsge0dLNgregR4MX6nJg5oo bpS9gAPhIWKi072xVwjJTvnB0IiQKxoKaQNhLFwvkVDMFFkJ7UIf+oDNa48WnLmlaNROEq 5h/cgHgPc0QS7fhyI9Ff7mQduVeKdQ5HLfc6YYwGKQbSuZEok9BR/stoGLsi4VpqGFRO3c EeLwmycKHbL72hmLC4HFwiReBONSFKPSBT/oOafm0ECnUZHz10SG/AKDCb3VVg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1762933772; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hjmsQNbabVrHMjgajgEZibUL+efg9RjKcTRD2S+ysQ8=; b=l0o/LkGfxoyEmPkG6koDawTBPXTEvwbAYcuza/5SjiqDSmJto9UrhdHQKSLqA10+aCQusg Q2gtdV349a9ij4Dg== From: Sebastian Andrzej Siewior To: Shakeel Butt 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: <20251112074930.mKu1J__U@linutronix.de> References: <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=utf-8 Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C61921C0005 X-Stat-Signature: i19mussni3so1drg534fm8qgq3s6kbh8 X-Rspam-User: X-HE-Tag: 1762933774-324806 X-HE-Meta: U2FsdGVkX18gur1+4AAlWqt3WwXNpfL+sNFbK3wEQ/PmobMcdfq8L+Li7kRCAziFrVIPXOrxoEUnFY4tkrzmRKgvFyFzTmuS1d+d2wV/hCzB/3Mz9wJJwBuDWxuc6eYo+AunGxZDIs0mN0iJb9tupAtcvQYMBEedS+RzkYr2dgYiXL9gLkXUSAV9G0RKLsUYwi/v0GBXQnb0oXcX5mRevIqq+2lb/S8glhJ7WPDjEubKXQXjD412m+UVodQAhb9qZpAGXTL81x4HwNFF2mbw5oI56LJt7JYe23WZPXEWvRbaMlXKmpZZZ/XEI1/z+wsutXwPTdOhb+ZR8om7Q0i1G0VDbZzlSdf/sbuBrc+TxHA3OS9uydgAghSst4+Dj5hLyQgA2bDUuHZu/698AymeHpKJhQf0LossvkAk2zBJGu0wdXT87XLcZJ475gds/z9UgsqjSgR2jFurc4sCacNDYmmPuuijmlQbOZrk1C9gdA/VHSmnVIUC6z5PIxpWzR2l9MVmzxQOMEOzhfuxddP9V/fzVQ0sgB/nenEl0XMDkFrSp7tAjwcrQTazeAgwDpk+Ps3hI85YQeenzIKp6/yA8KTqxI0Od1ruYC2fGsGL6jzd4SXCRSST22ynQh1lBqyNRdS7LXX1SvY3ey+vtguJY5/5xCibJw26g4zZg5ck0Bd0R3kSa1xB5FLifHBSQsGbU9RjAmvQGjUhyZchbtWellz8XspNcg0A2fS5ye5EyHdOpZJl1+/8b9DhdsBnFAPD4lcYmOlLuCggb+fxOyC87+cZ3Zq84xOUULaBAFcibhSirbMl9KNJ64GtuRlPqe6r4MxG2bLdcrBwSvvr0AUpd+9HYUuez6tEHlXwRQXaa6BMvzEQlZHANxy0P3e67eFLbrA4ucApgGzjv9G9Ze+to+PyDKcuMs73kt0cjyyMSHD4BcyrqnBX40pa15dbBNGCu6cvd5iKe1HYN9usqsD oJr+f0Z7 pAAF8YxqbUavkTEWd98HZ2zRGNVNOW+jERhsUvhBqb8yTrUqWGbSrd0o1UxOjmaHakCVIiNvosuK27Di6mazL4Zfzuxyy9ssYsByr6L0jz3XfUICbKX1ZAs2XJsniIGldkvbLWAOMwy2rZZM3IrtOB12BjxHB7L8fHrr9fngUmYOgXY9eYBxQG5k2S1Vf9PCNSkB/oDCV0J1P20jbCF4Zom+GKZKJIPYxJ8RANG9bHpkytPjBO1j0+kUNWg== 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 2025-11-11 08:44:14 [-0800], Shakeel Butt wrote: > 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? Yes. The local_irq_save() is not strictly needed but I am fine with it to keep it simple. The inner part is just counting. Sebastian