linux-kernel - Re: [PATCHSET] block, mempool, percpu: implement percpu mempool and fix blkcg percpu alloc deadlock

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Message-Id: <20111222175834.66559c8b.akpm@linux-foundation.org>
Date:	Thu, 22 Dec 2011 17:58:34 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, avi@...hat.com, nate@...nel.net,
	cl@...ux-foundation.org, oleg@...hat.com, axboe@...nel.dk,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHSET] block, mempool, percpu: implement percpu mempool and
 fix blkcg percpu alloc deadlock

On Thu, 22 Dec 2011 20:40:43 -0500 Vivek Goyal <vgoyal@...hat.com> wrote:

> That's why the need of per cpu data structures to make stat collection
> lockless.

btw, (and this is a common refrain): was there any reason for avoiding
using percpu_counters here?

afacit these stats don't have the transient-negative-number problem
because they're purely upcounters, but percpu_counters would be helpful
when num_online_cpus is much less than num_possible_cpus.  Plus it would
avoid implementing yet another hand-coded percpu_counter...

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