linux-kernel - Re: [patch]block: fix ioc locking warning

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Date:	Mon, 06 Feb 2012 21:16:06 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Tejun Heo <tj@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Shaohua Li <vivek.goyal2008@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Knut Petersen <Knut_Petersen@...nline.de>, mroos@...ux.ee
Subject: Re: [patch]block: fix ioc locking warning

On 2012-02-06 18:27, Tejun Heo wrote:
> Hello,
> 
> On Mon, Feb 06, 2012 at 08:58:49AM -0800, Linus Torvalds wrote:
>> On Mon, Feb 6, 2012 at 8:44 AM, Tejun Heo <tj@...nel.org> wrote:
>>>
>>> Yeah, this seems better to me.  Jens, if you're gonna amend the
>>> commit, please consider collapsing the following patch into the
>>> original patch too.  Thanks.
>>
>> Guys, is it *really* worth it to do all these crazy games?
>>
>> How bad is it to just always use the async freeing, instead of this
>> clearly very fragile crazy direct-freeing-with-serious-locking-issues
>> thing?
> 
> It's one wq scheduling on exit for any task which has issued an IO.  I
> don't think it would matter except for task fork/exit microbenchs (or
> workloads which approximate to that).  I'll get some measurements and
> strip the optimization if it doesn't really show up.

One (arguably stupid) thing that some users do do is something like:

$ find . -exec grep foo '{}' \;

So that would probably be a good pathological test case for this.

-- 
Jens Axboe

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