Date: Thu, 3 Nov 2005 20:52:02 -0800
From: Andrew Morton <akpm@osdl.org>
To: Badari Pulavarty <pbadari@gmail.com>
Cc: jdike@addtoit.com, rob@landley.net, nickpiggin@yahoo.com.au, gh@us.ibm.com,
       mingo@elte.hu, kamezawa.hiroyu@jp.fujitsu.com, haveblue@us.ibm.com,
       mel@csn.ul.ie, mbligh@mbligh.org, kravetz@us.ibm.com,
       linux-mm@kvack.org, linux-kernel@vger.kernel.org,
       lhms-devel@lists.sourceforge.net
Subject: Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19
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Badari Pulavarty <pbadari@gmail.com> wrote:
>
>  > With Badari's patch and UML memory hotplug, the infrastructure is
>  > there to make this work.  The one thing I'm puzzling over right now is
>  > how to measure memory pressure.
> 
>  Yep. This is the exactly the issue other product groups normally raise
>  on Linux. How do we measure memory pressure in linux ? Some of our
>  software products want to grow or shrink their memory usage depending
>  on the memory pressure in the system. Since most memory is used for
>  cache, "free" really doesn't indicate anything -they are monitoring
>  info in /proc/meminfo and swapping rates to "guess" on the memory
>  pressure. They want a clear way of finding out "how badly" system
>  is under memory pressure. (As a starting point, they want to find out
>  out of "cached" memory - how much is really easily "reclaimable" 
>  under memory pressure - without swapping). I know this is kind of 
>  crazy, but interesting to think about :)

Similarly, that SGI patch which was rejected 6-12 months ago to kill off
processes once they started swapping.  We thought that it could be done
from userspace, but we need a way for userspace to detect when a task is
being swapped on a per-task basis.

I'm thinking a few numbers in the mm_struct, incremented in the pageout
code, reported via /proc/stat.
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