linux-kernel - Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

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Date:	Thu, 12 Apr 2007 16:42:09 -0700
From:	William Lee Irwin III <wli@...omorphy.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

On Thu, 12 Apr 2007 16:10:50 -0700 William Lee Irwin III <wli@...omorphy.com> wrote:
>> This solves a real-life problem for Oracle system monitoring software
>> (specifically EM). Among the tasks it must carry out is determining
>> per-process memory footprint of a set of cooperating tasks (i.e. Oracle
>> processes). RSS is inadequate for this due to page sharing; this work
>> provides sufficient information to determine what EM needs.

On Thu, Apr 12, 2007 at 04:32:35PM -0700, Andrew Morton wrote:
> Not a good idea to expose raw flags in this manner - it changes at the drop
> of a hat.  We'd need to also expose the kernel's PG_foo-to-bitnumber
> mapping to make this viable.
> Not a good idea to use page->_count: page_count() will be more stable. 
> Otherwise OK, I guess: the interpretation of the page refcount is unlikely
> to change much over time.

EM wants to determine page_mapcount() for the most part for the
purposes of determining "uniquely attributable RSS" (my ca. 2004
nomenclature) or "proportional RSS" (mpm's more recent nomenclature);
as things now stand it will have to infer them by maintaining a table
of pfn's and mappings thereof, but at least that can be done with it.


-- wli
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