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

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Message-ID: <c1be5b75-d17b-2bbf-8bd2-4e6ade54bdae@virtuozzo.com>
Date:   Tue, 5 Jun 2018 11:48:49 +0300
From:   Kirill Tkhai <ktkhai@...tuozzo.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Michal Hocko <mhocko@...nel.org>
Cc:     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 01.06.2018 18:25, 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.
> 
>> 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.

It was triggered on a server, where many VPS of many people are hosted.
Sorry, I have no an idea what they did.

Kirill