linux-kernel - Re: [RFC v2 0/5] cgroup-aware unbound workqueues

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Date:   Thu, 6 Jun 2019 09:15:26 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Daniel Jordan <daniel.m.jordan@...cle.com>, hannes@...xchg.org,
        jiangshanlai@...il.com, lizefan@...wei.com, bsd@...hat.com,
        dan.j.williams@...el.com, dave.hansen@...el.com,
        juri.lelli@...hat.com, mhocko@...nel.org, peterz@...radead.org,
        steven.sistare@...cle.com, tglx@...utronix.de,
        tom.hromatka@...cle.com, vdavydov.dev@...il.com,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [RFC v2 0/5] cgroup-aware unbound workqueues

Hi Tejun,

On Wed, Jun 05, 2019 at 06:53:19AM -0700, Tejun Heo wrote:
> Hello, Daniel.
> 
> On Wed, Jun 05, 2019 at 09:36:45AM -0400, Daniel Jordan wrote:
> > My use case for this work is kernel multithreading, the series formerly known
> > as ktask[2] that I'm now trying to combine with padata according to feedback
> > from the last post.  Helper threads in a multithreaded job may consume lots of
> > resources that aren't properly accounted to the cgroup of the task that started
> > the job.
> 
> Can you please go into more details on the use cases?

If I remember correctly, the original Bandan's work was about using
workqueues instead of kthreads in vhost. 
 
> For memory and io, we're generally going for remote charging, where a
> kthread explicitly says who the specific io or allocation is for,
> combined with selective back-charging, where the resource is charged
> and consumed unconditionally even if that would put the usage above
> the current limits temporarily.  From what I've been seeing recently,
> combination of the two give us really good control quality without
> being too invasive across the stack.
> 
> CPU doesn't have a backcharging mechanism yet and depending on the use
> case, we *might* need to put kthreads in different cgroups.  However,
> such use cases might not be that abundant and there may be gotaches
> which require them to be force-executed and back-charged (e.g. fs
> compression from global reclaim).
> 
> Thanks.
> 
> -- 
> tejun
> 

-- 
Sincerely yours,
Mike.