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

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Message-ID: <393a4509-9b05-45b8-8496-699ace9a5438@kylinos.cn>
Date: Mon, 11 Aug 2025 17:29:23 +0800
From: Zihuan Zhang <zhangzihuan@...inos.cn>
To: Oleg Nesterov <oleg@...hat.com>
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>,
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 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>,
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 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,
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 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 6/9] freezer: Set default freeze priority for
 zombie tasks

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 loop.
> Oleg.
>