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

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Message-ID: <20080924234213.GC8598@csn.ul.ie>
Date:	Thu, 25 Sep 2008 00:42:13 +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 12:23), Dave Hansen didst pronounce:
> On Wed, 2008-09-24 at 20:11 +0100, Mel Gorman wrote:
> > I don't get what you mean by it being sprinkled in each smaps file. How
> > would you present the data?
> 
> 1. figure out what the file path is from smaps
> 2. look up the mount
> 3. look up the page sizes from the mount's information
> 
> > > We should be able to figure out which
> > > mount the file is from and, from there, maybe we need some per-mount
> > > information exported.  
> > 
> > Per-mount information is already exported and you can infer the data about
> > huge pagesizes. For example, if you know the default huge pagesize (from
> > /proc/meminfo), and the file is on hugetlbfs (read maps, then /proc/mounts)
> > and there is no pagesize= mount option (mounts again), you could guess what the
> > hugepage that is backing a VMA is. Shared memory segments are a little harder
> > but again, you can infer the information if you look around for long enough.
> > 
> > However, this is awkward and not very user-friendly. With the patches (minus
> > MMUPageSize as I think we've agreed to postpone that), it's easy to see what
> > pagesize is being used at a glance. Without it, you need to know a fair bit
> > about hugepages are implemented in Linux to infer the information correctly.
> 
> I agree completely.  But, if we consider this a user ABI thing, then
> we're stuck with it for a long time, and we better make it flexible
> enough to at least contain the gunk we're planning on adding in a small
> number of years, like the fallback.  We don't want to be adding this
> stuff if it isn't going to be stable.
> 

This could also be done as

KernelPageSize == Kernel page size that is ideally used in this VMA

and later

MixedPageSize == Breakdown of the pagesizes that are used in the VMA

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