linux-kernel - Re: [PATCH 2/6] change alloc function in pcpu_alloc

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Date:	Fri, 16 Apr 2010 15:13:09 -0400
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Minchan Kim <minchan.kim@...il.com>, Tejun Heo <tj@...nel.org>,
	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Bob Liu <lliubbo@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 2/6] change alloc function in pcpu_alloc_pages

On Fri, 2010-04-16 at 11:07 -0500, Christoph Lameter wrote:
> On Thu, 15 Apr 2010, Minchan Kim wrote:
> 
> > I don't want to remove alloc_pages for UMA system.
> 
> alloc_pages is the same as alloc_pages_any_node so why have it?
> 
> > #define alloc_pages alloc_page_sexact_node
> >
> > What I want to remove is just alloc_pages_node. :)
> 
> Why remove it? If you want to get rid of -1 handling then check all the
> callsites and make sure that they are not using  -1.
> 
> Also could you define a constant for -1? -1 may have various meanings. One
> is the local node and the other is any node. 

NUMA_NO_NODE is #defined as (-1) and can be used for this purpose.  '-1'
has been replaced by this in many cases.   It can be interpreted as "No
node specified" == "any node is acceptable".  But, it also has multiple
meanings.  E.g., in the hugetlb sysfs attribute and sysctl functions it
indicates the global hstates [all nodes] vs a per node hstate.  So, I
suppose one could define a NUMA_ANY_NODE, to make the intention clear at
the call site.

I believe that all usage of -1 to mean the local node has been removed,
unless I missed one.  Local allocation is now indicated by a mempolicy
mode flag--MPOL_F_LOCAL.  It's treated as a special case of
MPOL_PREFERRED.

> The difference is if memory
> policies are obeyed or not. Note that alloc_pages follows memory policies
> whereas alloc_pages_node does not.
> 
> Therefore
> 
> alloc_pages() != alloc_pages_node(  , -1)
> 
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