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From: Shakeel Butt To: Vlastimil Babka , Sebastian Andrzej Siewior Cc: 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 Subject: Re: [PATCH] memcg: decouple memcg_hotplug_cpu_dead from stock_lock Message-ID: References: <20250410210623.1016767-1-shakeel.butt@linux.dev> <0e9e2d5d-ec64-4ad4-a184-0c53832ff565@suse.cz> <8cce9a28-3b02-4126-a150-532e92c0e7f8@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: BB3BA40002 X-Stat-Signature: eqs38954euxrc7uompnpay4mp6ephgik X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1744653337-454555 X-HE-Meta: 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 zdMoJsyF 3jsaUD3tjJT0avhw5Ar3Z1ILBahsVT6WcPtvlV6/J6SDP0gc9eHDTxgbeterLGvl8HEBExSn+dzmWQpUGWFFGtNKiIsxq1a3MrGvRK3iQua2DK5aAgfkBUrUXAlpsYWLolup/j9ijKEUoZR9GPxrqa01Xn0C5VWAMJSsX658t1CUI4H3rDrQE1YZmoAIuA+hJHtVm7AGj9yeeKt214BUP33Ey3ThWXElWuDzMmIwFu7I0dm66Bc+qhKcwvWjmTdwqHC7o 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 Fri, Apr 11, 2025 at 02:12:46PM -0400, Shakeel Butt wrote: > On Fri, Apr 11, 2025 at 2:06 PM Vlastimil Babka wrote: > > > > 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 :) > > Sorry, I wanted to say local_irq_save() here instead of local_lock_irqsave(). > > > 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. > > Basically I don't want to use stock_lock here. Maybe I should explore > adding a new local_lock for __mod_memcg_lruvec_state and > __mod_memcg_state. Vlastimil & Sebastian, if you don't have a strong opinion/push-back on this patch then I will keep it as is. However I am planning to rework the memcg stats (& vmstats) to see if I can use dedicated local_lock for them and able to modify them in any context.