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

From: Mike Rapoport <rppt@linux.ibm.com>
To: Tejun Heo <tj@kernel.org>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>,
	hannes@cmpxchg.org, jiangshanlai@gmail.com, lizefan@huawei.com,
	bsd@redhat.com, dan.j.williams@intel.com, dave.hansen@intel.com,
	juri.lelli@redhat.com, mhocko@kernel.org, peterz@infradead.org,
	steven.sistare@oracle.com, tglx@linutronix.de,
	tom.hromatka@oracle.com, vdavydov.dev@gmail.com,
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [RFC v2 0/5] cgroup-aware unbound workqueues
Date: Thu, 6 Jun 2019 09:15:26 +0300	[thread overview]
Message-ID: <20190606061525.GD23056@rapoport-lnx> (raw)
In-Reply-To: <20190605135319.GK374014@devbig004.ftw2.facebook.com>

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.