linux-kernel - Re: [PATCH v6] block: loop: avoiding too many pending per work I/O

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Message-ID: <CACVXFVOMG62=31Z-9e2oMUFObMrwZVHc8nN6EUAqtDMrrwo5Uw@mail.gmail.com>
Date:	Sat, 2 May 2015 23:09:12 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Jens Axboe <axboe@...nel.dk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Justin M. Forbes" <jforbes@...oraproject.org>,
	Jeff Moyer <jmoyer@...hat.com>, "v4.0" <stable@...r.kernel.org>
Subject: Re: [PATCH v6] block: loop: avoiding too many pending per work I/O

On Fri, May 1, 2015 at 11:47 PM, Tejun Heo <tj@...nel.org> wrote:
> On Fri, May 01, 2015 at 08:05:45AM -0700, Christoph Hellwig wrote:
>> > Maybe just cap max_active to NR_OF_LOOP_DEVS * 16 or sth?  But idk,
>> > how many concurrent workers are we talking about and why are we
>> > capping per-queue concurrency from worker pool side instead of command
>> > tag side?
>>
>> Also we probably should have per device workqueues to start with..
>
> Yeah, that's an option.  The only thing is that each workqueue would

I guess we have to do that because of nested loop devices.

> have to be tagged WQ_RESCUER and end up with separate rescuer task,
> which usually isn't big a deal but there are setups where a lot of
> loop devices are used and it may sting a bit.

The work queue can be allocated just before the loop is to be used
and destroyed when it needn't.

I will figure out one patch to do that.

>
> Thanks.
>
> --
> tejun
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