linux-kernel - Re: [PATCH 4/4] maps: /proc/<pid>/pmaps interface

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Date:	Thu, 16 Aug 2007 21:38:46 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Fengguang Wu <wfg@...l.ustc.edu.cn>
Cc:	Andrew Morton <akpm@...l.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	David Rientjes <rientjes@...gle.com>,
	John Berthels <jjberthels@...il.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] maps: /proc/<pid>/pmaps interface - memory maps in granularity of pages

On Fri, Aug 17, 2007 at 06:05:20AM +0800, Fengguang Wu wrote:
> Show a process's page-by-page address space infomation in /proc/<pid>/pmaps.
> It helps to analyze applications' memory footprints in a comprehensive way.
> 
> Pages share the same states are grouped into a page range.
> For each page range, the following fields are exported:
> 	- first page index
> 	- number of pages in the range
> 	- well known page/pte flags
> 	- number of mmap users
> 
> Only page flags not expected to disappear in the near future are exported:
> 
> 	Y:young R:referenced A:active U:uptodate P:ptedirty D:dirty W:writeback
...

> The concern of dataset size is taken care of by working in a sparse way:
> 
> 1) It will only generate output for resident pages, that normally is
> much smaller than the mapped size. Take my shell for example, the
> (size:rss) ratio is (7:1)!
> 
> wfg ~% cat /proc/$$/smaps |grep Size|sum
> sum      50552.000
> avg        777.723
> 
> wfg ~% cat /proc/$$/smaps |grep Rss|sum
> sum       7604.000
> avg        116.985
> 
> 2) The page range trick suppresses more output.
> 
> It's interesting to see that the seq_file interface demands some
> more programming efforts, and provides such flexibility as well.

I'm so-so on this. 

On the downside:

- requires lots of parsing
- isn't random-access
- probably significantly slower than pagemap

-- 
Mathematics is the supreme nostalgia of our time.
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