linux-kernel - Re: [PATCH RESEND 2/4] cpuset: simplify cpuset_node

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Date:	Mon, 27 Oct 2014 11:18:06 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Christoph Lameter <cl@...ux.com>,
	Zefan Li <lizefan@...wei.com>,
	Pekka Enberg <penberg@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH RESEND 2/4] cpuset: simplify cpuset_node_allowed API

On Mon, Oct 20, 2014 at 03:50:30PM +0400, Vladimir Davydov wrote:
> Current cpuset API for checking if a zone/node is allowed to allocate
> from looks rather awkward. We have hardwall and softwall versions of
> cpuset_node_allowed with the softwall version doing literally the same
> as the hardwall version if __GFP_HARDWALL is passed to it in gfp flags.
> If it isn't, the softwall version may check the given node against the
> enclosing hardwall cpuset, which it needs to take the callback lock to
> do.
> 
> Such a distinction was introduced by commit 02a0e53d8227 ("cpuset:
> rework cpuset_zone_allowed api"). Before, we had the only version with
> the __GFP_HARDWALL flag determining its behavior. The purpose of the
> commit was to avoid sleep-in-atomic bugs when someone would mistakenly
> call the function without the __GFP_HARDWALL flag for an atomic
> allocation. The suffixes introduced were intended to make the callers
> think before using the function.
> 
> However, since the callback lock was converted from mutex to spinlock by
> the previous patch, the softwall check function cannot sleep, and these
> precautions are no longer necessary.
> 
> So let's simplify the API back to the single check.
> 
> Suggested-by: David Rientjes <rientjes@...gle.com>
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>
> Acked-by: Christoph Lameter <cl@...ux.com>
> Acked-by: Zefan Li <lizefan@...wei.com>

Applied 1-2 to cgroup/for-3.19-cpuset-api-simplification which
contains only these two patches on top of v3.18-rc2 and will stay
stable.  sl[au]b trees can pull it in or I can take the other two
patches too.  Please let me know how the other two should be routed.

Thanks.

-- 
tejun
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