linux-kernel - Re: [PATCH 0/4] exit: Make unlikely case in mm_update_next

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Message-ID: <87y3fyv88o.fsf@xmission.com>
Date:   Fri, 01 Jun 2018 10:25:59 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>, akpm@...ux-foundation.org,
        peterz@...radead.org, oleg@...hat.com, viro@...iv.linux.org.uk,
        mingo@...nel.org, paulmck@...ux.vnet.ibm.com,
        keescook@...omium.org, riel@...hat.com, tglx@...utronix.de,
        kirill.shutemov@...ux.intel.com, marcos.souza.org@...il.com,
        hoeun.ryu@...il.com, pasha.tatashin@...cle.com, gs051095@...il.com,
        dhowells@...hat.com, rppt@...ux.vnet.ibm.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable

Michal Hocko <mhocko@...nel.org> writes:

> On Fri 01-06-18 09:32:42, Eric W. Biederman wrote:
>> Michal Hocko <mhocko@...nel.org> writes:
> [...]
>> > Group leader exiting early without tearing down the whole thread
>> > group should be quite rare as well. No question that somebody might do
>> > that on purpose though...
>> 
>> The group leader exiting early is a completely legitimate and reasonable
>> thing to do, even if it is rare.
>
> I am not saying it isn't legitimate. But the most common case is the
> main thread waiting for its threads or calling exit which would tear the
> whole group down. Is there any easy way to achieve this other than tkill
> to group leader? Calling exit(3) from the leader performs group exit
> IIRC.

pthread_exit from the group leader.

> I am not arguing this is non-issue. And it certainly is a problem once
> somebody wants to be nasty... I was more interested how often this
> really happens for sane workloads.

That is a fair question.  All I know for certain is that whatever Kirill
Tkhai's workload was it was triggering this the slow path.

Eric