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Fri, 11 Apr 2025 18:06:17 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id w+QBDhla+WemSQAAD6G6ig (envelope-from ); Fri, 11 Apr 2025 18:06:17 +0000 Message-ID: <8cce9a28-3b02-4126-a150-532e92c0e7f8@suse.cz> Date: Fri, 11 Apr 2025 20:06:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] memcg: decouple memcg_hotplug_cpu_dead from stock_lock Content-Language: en-US To: Shakeel Butt , Sebastian Andrzej Siewior Cc: Shakeel Butt , Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Yosry Ahmed , Waiman Long , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team References: <20250410210623.1016767-1-shakeel.butt@linux.dev> <0e9e2d5d-ec64-4ad4-a184-0c53832ff565@suse.cz> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: EDC50C0005 X-Stat-Signature: dnp6jsfegfm8nsooefuyzig7nffe5d7e X-HE-Tag: 1744394778-265467 X-HE-Meta: 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 fHkilbRt RaBeId3xk26xfltuDJUJZhpsQBYrKiEQf2/0E4sUNtNFv6Yne5L3wJewDZMqPex0mYjvs4IQp5Vb6IM/upeVp7gXSwbcHXTxJV/nolF5lcjY7y8af5kcGScDE1eErNZBCS/P9e5/aA772vGNmboZFKg+OV610UunWveM3GUotxpFQSVIQESLqn4y6FreUPU4Ol0IG92JDkwdBe8yX3MYlWQPfurZs91et0CsWOaXuXfS+QT/SFiv0cPKUWC7xEWzrh/iW8cg3xXHrLL3pvaY5/dZmL7L/Y/C5HSljbpd5hcJ0mH9+tl8ahsFmgNcUb1dnq54ZIYXsKfAbfWA9sQjvktjsTpY8uZC53gHQsidZ2zilISRCKBQe0zf2l79LA+Lzl1Jkp6v2a+rDSrcd7nQyE/fl4g== 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 4/11/25 19:54, Shakeel Butt wrote: > (my migadu/linux.dev stopped working and I have to send through gmail, > sorry for any formatting issue) > > I don't see how local_irq_save() will break anything. We are working on > a stock of a dead remote cpu. We actually don't even need to disable irq > or need local cpu's local_lock. It is actually the calls to > __mod_memcg_lruvec_state() and __mod_memcg_state() in > __drain_obj_stock() which need irq-disabled on non-RT kernels and for > RT-kernels they already have preempt_disable_nested(). > > Disabling irq even on RT seems excessive but this is not a performance > critical code, so I don't see an issue unless there is > local_lock_irqsave() alternative which does not disables irqs on RT > kernels. local_lock_irqsave() does not disable irqs on RT kernels :) so keeping local_lock as is would do the irq disable on !RT and be more RT-friendly on RT. It's just wrong from the logical scope of the lock to perform it on a different cpu than the stock we modify. If one day we have some runtime checks for that, they would complain.