linux-kernel - Re: [PATCH v2] sched/core: Don't use dying mm as active

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Date:   Mon, 29 Jul 2019 20:58:53 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v2] sched/core: Don't use dying mm as active_mm of
 kthreads

On Mon 29-07-19 11:27:35, Waiman Long wrote:
> On 7/29/19 5:12 AM, Michal Hocko wrote:
> > On Sat 27-07-19 13:10:47, Waiman Long wrote:
> >> It was found that a dying mm_struct where the owning task has exited
> >> can stay on as active_mm of kernel threads as long as no other user
> >> tasks run on those CPUs that use it as active_mm. This prolongs the
> >> life time of dying mm holding up memory and other resources like swap
> >> space that cannot be freed.
> > IIRC use_mm doesn't pin the address space. It only pins the mm_struct
> > itself. So what exactly is the problem here?
> 
> As explained in my response to Peter, I found that resource like swap
> space were depleted even after the exit of the offending program in a
> mostly idle system. This patch is to make sure that those resources get
> freed after program exit ASAP.

Could you elaborate more? How can a mm counter (do not confuse with
mm_users) prevent address space to be torn down on exit?


-- 
Michal Hocko
SUSE Labs