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

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Date:   Mon, 4 Jun 2018 08:54:25 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
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

On Fri 01-06-18 10:25:59, Eric W. Biederman wrote:
> 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.

Right, forgot to mention this one but this would be quite exotic, right?


> > 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.

Yeah, that was exactly why I've asked that originally. It must be
something pretty special ;)
-- 
Michal Hocko
SUSE Labs