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

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Message-Id: <20120223152223.43c72ccb.akpm@linux-foundation.org>
Date:	Thu, 23 Feb 2012 15:22:23 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	vgoyal@...hat.com, 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
Subject: Re: [PATCHSET] mempool, percpu, blkcg: fix percpu stat allocation
 and remove stats_lock

On Thu, 23 Feb 2012 15:12:04 -0800
Tejun Heo <tj@...nel.org> wrote:

> On Thu, Feb 23, 2012 at 03:01:23PM -0800, Tejun Heo wrote:
> > Hmmm... going through the thread again, ah, okay, I forgot about that
> > completely.  Yeah, that is an actual problem.  Both __GFP_WAIT which
> > isn't GFP_KERNEL and GFP_KERNEL are valid use cases.  I guess we'll be
> > building async percpu pool in blkcg then.  Great.  :(
> 
> Vivek, you win. :) Can you please refresh the async alloc patch on top
> of blkcg-stacking branch?  I'll rool that into this series and drop
> the mempool stuff.

I forget how those patches work, but they might be vulnerable to the
same issue.  If the block layer can handle the failed allocation
attempt and retry at the next I/O event then I guess that would be
acceptable; we'd lose a bit of statistical info occasionally, but who
cares.

But ISTR that we can't handle allocation failures here?
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