linux-kernel - Re: [PATCHSET] mempool, percpu, blkcg: fix percpu stat allocation and remove stats

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Date:	Sun, 26 Feb 2012 22:11:46 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	axboe@...nel.dk, hughd@...gle.com, avi@...hat.com, nate@...nel.net,
	cl@...ux-foundation.org, linux-kernel@...r.kernel.org,
	dpshah@...gle.com, ctalbott@...gle.com, rni@...gle.com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHSET] mempool, percpu, blkcg: fix percpu stat allocation
 and remove stats_lock

On Sun, Feb 26, 2012 at 06:44:21AM +0900, Tejun Heo wrote:
> Hello, Vivek.
> 
> On Fri, Feb 24, 2012 at 09:20:33AM -0500, Vivek Goyal wrote:
> > Ok. I will write a patch. Things have changed a lot since last time.
> > I think there is only one tricky part and that is waiting for any
> > scheduled work to finish during blkg destruction.  Because group destruction
> > happens under both queue and blkcg spin locks, I think I will have to take
> > the group off list, drop locks, wait for worker thread to finish and then
> > take locks again and walk through list again to kill remaining groups.
> 
> Rather than embedding work_struct into blkg and tying work and blkg
> destruction, why not just create a spinlock protected alloc-pending
> list?  On blkg creation, link blkg onto that list and kick shared work
> item and on destruction, just unlink it.  Worker function can walk the
> list and try to alloc for all and reschedule if alloc fails.

Ok. This sounds better than embeding work_struct in blkg, I can embed it
in request_queue and make the worker walk the list of blkg pending 
alloc of stats. Will try that. Thanks for the idea.

Thanks
Vivek
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