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

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Date:   Thu, 26 Apr 2018 15:07:00 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
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,
        ebiederm@...ssion.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 Thu 26-04-18 14:00:19, Kirill Tkhai wrote:
> This function searches for a new mm owner in children and siblings,
> and then iterates over all processes in the system in unlikely case.
> Despite the case is unlikely, its probability growths with the number
> of processes in the system. The time, spent on iterations, also growths.
> I regulary observe mm_update_next_owner() in crash dumps (not related
> to this function) of the nodes with many processes (20K+), so it looks
> like it's not so unlikely case.

Did you manage to find the pattern that forces mm_update_next_owner to
slow paths? This really shouldn't trigger very often. If we can fallback
easily then I suspect that we should be better off reconsidering
mm->owner and try to come up with something more clever. I've had a
patch to remove owner few years back. It needed some work to finish but
maybe that would be a better than try to make non-scalable thing suck
less.

-- 
Michal Hocko
SUSE Labs