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From: Roman Gushchin <roman.gushchin@linux.dev>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org,  LKML <linux-kernel@vger.kernel.org>,
	 Peter Zijlstra <peterz@infradead.org>,
	 Johannes Weiner <hannes@cmpxchg.org>,
	Michal Hocko <mhocko@kernel.org>,
	 Shakeel Butt <shakeel.butt@linux.dev>,
	Muchun Song <muchun.song@linux.dev>,
	 cgroups@vger.kernel.org,
	 Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] memcg: Optimize exit to user space
Date: Wed, 13 Aug 2025 08:45:02 -0700	[thread overview]
Message-ID: <87ectfgr9d.fsf@linux.dev> (raw)
In-Reply-To: <87tt2b6zgs.ffs@tglx> (Thomas Gleixner's message of "Wed, 13 Aug 2025 16:57:55 +0200")

Thomas Gleixner <tglx@linutronix.de> writes:

> memcg uses TIF_NOTIFY_RESUME to handle reclaiming on exit to user
> space. TIF_NOTIFY_RESUME is a multiplexing TIF bit, which is utilized by
> other entities as well.
>
> This results in a unconditional mem_cgroup_handle_over_high() call for
> every invocation of resume_user_mode_work(), which is a pointless
> exercise as most of the time there is no reclaim work to do.
>
> Especially since RSEQ is used by glibc, TIF_NOTIFY_RESUME is raised
> quite frequently and the empty calls show up in exit path profiling.
>
> Optimize this by doing a quick check of the reclaim condition before
> invoking it.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Roman Gushchin <roman.gushchin@linux.dev>
> Cc: Shakeel Butt <shakeel.butt@linux.dev>
> Cc: Muchun Song <muchun.song@linux.dev>
> Cc: Andrew Morton <akpm@linux-foundation.org>

Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>

Thanks!

  reply	other threads:[~2025-08-13 15:45 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-08-13 14:57 [PATCH] memcg: Optimize exit to user space Thomas Gleixner
2025-08-13 15:45 ` Roman Gushchin [this message]
2025-08-13 16:17 ` Johannes Weiner
2025-08-13 17:19 ` Shakeel Butt
2025-08-13 21:25   ` Thomas Gleixner
2025-08-13 22:40   ` Andrew Morton

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