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

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Message-ID: <20141027155629.GS4436@htj.dyndns.org>
Date:	Mon, 27 Oct 2014 11:56:29 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	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 27, 2014 at 06:36:54PM +0300, Vladimir Davydov wrote:
> Hi Tejun,
> 
> On Mon, Oct 27, 2014 at 11:18:06AM -0400, Tejun Heo wrote:
> > 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.
> 
> JFYI, Andrew merged all four patches in his mmotm tree.
> 
> FWIW, there's a typo in this patch recently found and fixed by Dan
> Carpenter. The fix is below.

Ah, cool.  I'll keep the cpuset patches and the fix in the cgroup tree
so that future dependent changes don't collide with them in -mm.
Andrew, please note that the first two patches in this series and
Dan's fix will appear in cgroup/for-3.19.

Thanks.

-- 
tejun
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