linux-kernel - Re: [RFC PATCH v1 6/9] freezer: Set default freeze priority for zombie tasks

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Message-ID: <20250811094252.GC11928@redhat.com>
Date: Mon, 11 Aug 2025 11:42:53 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	David Hildenbrand <david@...hat.com>,
	Michal Hocko <mhocko@...e.com>, Jonathan Corbet <corbet@....net>,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	len brown <len.brown@...el.com>, pavel machek <pavel@...nel.org>,
	Kees Cook <kees@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Nico Pache <npache@...hat.com>, xu xin <xu.xin16@....com.cn>,
	wangfushuai <wangfushuai@...du.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jeff Layton <jlayton@...nel.org>, Al Viro <viro@...iv.linux.org.uk>,
	Adrian Ratiu <adrian.ratiu@...labora.com>, linux-pm@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 6/9] freezer: Set default freeze priority for
 zombie tasks

On 08/11, Zihuan Zhang wrote:
> 
> 在 2025/8/8 22:29, Oleg Nesterov 写道:
> >On 08/07, Zihuan Zhang wrote:
> >>@@ -6980,6 +6981,7 @@ void __noreturn do_task_dead(void)
> >>  	current->flags |= PF_NOFREEZE;
> >>
> >>  	__schedule(SM_NONE);
> >>+	freeze_set_default_priority(current, FREEZE_PRIORITY_NEVER);
> >>  	BUG();
> >But this change has no effect?
> >
> >Firstly, this last __schedule() should not return, note the BUG() we have.
> >
> >Secondly, this zombie is already PF_NOFREEZE, freeze_task() will return
> >false anyway.
> Sorry, but in our tests with a large number of zombie tasks, returning early
> reduced the overhead. Even though freeze_task() would return false for
> PF_NOFREEZE, skipping the extra path still saved time in our suspend/freezer

https://lore.kernel.org/all/20250707084214.GD1613200@noisy.programming.kicks-ass.net/

Anyway the patch makes no sense in its current form, see my note
about __schedule() above.

Oleg.