linux-kernel - Re: [PATCH 1/1] doc, mempolicy: Fix wrong document in numa_memory

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Message-ID: <alpine.DEB.2.02.1404110353440.30610@chino.kir.corp.google.com>
Date:	Fri, 11 Apr 2014 03:54:53 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Randy Dunlap <rdunlap@...radead.org>
cc:	Tang Chen <tangchen@...fujitsu.com>, hannes@...xchg.org,
	mhocko@...e.cz, bsingharora@...il.com,
	kamezawa.hiroyu@...fujitsu.com, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, guz.fnst@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/1] doc, mempolicy: Fix wrong document in
 numa_memory_policy.txt

On Thu, 10 Apr 2014, Randy Dunlap wrote:

> On 04/01/2014 08:53 PM, Tang Chen wrote:
> > In document numa_memory_policy.txt, the following examples for flag
> > MPOL_F_RELATIVE_NODES are incorrect.
> > 
> > 	For example, consider a task that is attached to a cpuset with
> > 	mems 2-5 that sets an Interleave policy over the same set with
> > 	MPOL_F_RELATIVE_NODES.  If the cpuset's mems change to 3-7, the
> > 	interleave now occurs over nodes 3,5-6.  If the cpuset's mems
> > 	then change to 0,2-3,5, then the interleave occurs over nodes
> > 	0,3,5.
> > 
> > According to the comment of the patch adding flag MPOL_F_RELATIVE_NODES,
> > the nodemasks the user specifies should be considered relative to the
> > current task's mems_allowed.
> > (https://lkml.org/lkml/2008/2/29/428)
> > 
> > And according to numa_memory_policy.txt, if the user's nodemask includes
> > nodes that are outside the range of the new set of allowed nodes, then
> > the remap wraps around to the beginning of the nodemask and, if not already
> > set, sets the node in the mempolicy nodemask.
> > 
> > So in the example, if the user specifies 2-5, for a task whose mems_allowed
> > is 3-7, the nodemasks should be remapped the third, fourth, fifth, sixth
> > node in mems_allowed.  like the following:
> > 
> > 	mems_allowed:       3  4  5  6  7
> > 
> > 	relative index:     0  1  2  3  4
> > 	                    5
> > 
> > So the nodemasks should be remapped to 3,5-7, but not 3,5-6.
> > 
> > And for a task whose mems_allowed is 0,2-3,5, the nodemasks should be
> > remapped to 0,2-3,5, but not 0,3,5.
> > 
> > 	mems_allowed:       0  2  3  5
> > 
> >         relative index:     0  1  2  3
> >                             4  5
> > 
> > 
> > Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
> 
> Wow.  This was not an April fools joke, right?
> 

It would have been a horrible joke if it was intended to be :)

> Have there been any acks of this?  I haven't seen any responses to it.
> 

Because everybody in the phonebook was cc'd on it except for the author 
who wrote it.

Tang, good catch.

Acked-by: David Rientjes <rientjes@...gle.com>
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