linux-kernel - Re: [PATCH prototype] [0/8] Predictive bitmaps for ELF executables

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Date:	Thu, 20 Mar 2008 01:15:20 +0100
From:	Diego Calleja <diegocg@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH prototype] [0/8] Predictive bitmaps for ELF executables

El Wed, 19 Mar 2008 02:04:40 -0700, Andrew Morton <akpm@...ux-foundation.org> escribió:

> Assuming that all users have the same access pattern might be inefficient,
> a little bit.  There might be some advantage to making it per-user, dunno.

In the Dark Side of operating systems, the prefetching system they use
can log several access patterns for a single executable, because a single
executable can have different behaviours even for the same user, depending
on what parameters the executable is passed and what COM machinery it
uses. For example, wmplayer.exe can play a dvd, rip a CD, listen to a music
stream, etc...diferent usages, different access patterns. Linux probably faces
the same problem (bash, cat...)

A alternative design for a userspace solution that doesn't needs LD_PRELOAD
is to use CONFIG_PROC_EVENTS to get notifications of what processes are
started, which can be used to poll its /proc files or try to preload data
(asynchronously, and a bit hacky maybe).

But if a kernel patch is really needed to implement this properly, maybe
it'd be worth to take a look at the prefetch project that the Ubuntu guys
are apparently going to merge in the next ubuntu development release (8.10)...
https://wiki.ubuntu.com/DesktopTeam/Specs/Prefetch

There are even kernel patches:
http://code.google.com/p/prefetch/source/browse/tags/soc2007-end/trunk/kernel-patches/2.6.22/submitted/0001-prefetch-core.diff
http://code.google.com/p/prefetch/source/browse/tags/soc2007-end/trunk/kernel-patches/2.6.22/submitted/0002-prefetch-boot.diff
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