linux-kernel - Re: [PATCH 1/2] Report the pagesize backing a VMA in /proc/pid/smaps

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Message-ID: <20080924171003.GD10837@csn.ul.ie>
Date:	Wed, 24 Sep 2008 18:10:04 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>, agl@...ibm.com,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 1/2] Report the pagesize backing a VMA in /proc/pid/smaps

On (24/09/08 09:06), Dave Hansen didst pronounce:
> On Wed, 2008-09-24 at 16:41 +0100, Mel Gorman wrote:
> > I admit it's ppc64-specific. In the latest patch series, I made this a
> > separate patch so that it could be readily dropped again for this reason.
> > Maybe an alternative would be to display MMUPageSize *only* where it differs
> > from KernelPageSize. Would that be better or similarly confusing?
> 
> I would also think that any arch implementing fallback from large to
> small pages in a hugetlbfs area (Adam needs to post his patches :) would
> also use this.
> 

Fair point. Maybe the thing to do is backburner this patch for the moment and
reintroduce it when/if an architecture supports demotion? The KernelPageSize
reporting in smaps and what the hpagesize in maps is still useful though
I believe. Any comment?

(future stuff from here on)

In the future if demotion does happen then the MMUPageSize information may
be genuinely useful instead of just a curious oddity on ppc64. As you point
out, Adam (added to cc) has worked on this area (starting with x86 demotion)
in the past but it's a while before it'll be considered for merging I believe.

That aside, more would need to be done with the page size reporting then
anyway. For example, it maybe indicate how much of each pagesize is in a VMA
or indicate that KernelPageSize is what is being requested but in reality
it is mixed like;

KernelPageSize:		2048 kB (mixed)

or

KernelPageSize:		2048 kB * 5, 4096 kB * 20

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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