linux-kernel - [ANNOUNCE] sreadahead-1.0

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Date:	Tue, 27 Jan 2009 12:06:59 -0800
From:	"Kok, Auke" <auke-jan.h.kok@...el.com>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	powertop ml <power@...host.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, srostedt@...hat.com
Subject: [ANNOUNCE] sreadahead-1.0

All,

we're happy to announce a major rewrite of sreadahead, and the release of version
1.0. This is a significant improvement in the way sreadahead works:

* sreadahead now will work on any filesystem;

  Sreadahead used to use an ioctl to retreive inserted timestamps from ext3
  inodes. This patch is now replaced with a generic open() syscall tracer,
  which will work on all filesystems.

* pack file generation is now integrated entirely in a single binary, and
  automatically done if the pack file is missing;

  Sreadahead is now a single-binary two-purpose program that either reads in
  the content needed, or generates this content. This reduces the chance that
  sreadahead is called incorrectly, but also makes installation a lot easier.
  Sreadahead can now be added to the boot system by inserting a single line
  in a startup script.

* pack file generation is now significantly faster than the old method;

  Sreadahead now uses a kernel tracer which provides with a sort-by-use list of
  all files opened. This removes the need for a special script to discover
  which files were opened at boot. This list is sorted and filtered in C
  code inside sreadahead which proves much faster. The old method took
  multiple seconds. New method sorts/filters 10k+ open trace calls in 0.16s
  on a regular desktop.

* sreadahead now accounts for kernel read_ahead_kb, reducing data read
  at boot time;

  While sreadahead reads "used" data into memory, the kernel reports more
  memory in use than actually used due to the in-kernel readahead function.
  In order to read significantly less data, sreadahead temporarily reduces
  this amount, saving significant amount of total IO time. This saves as
  much as 8 out of 64Mb on a regular fedora core installation.

Sreadahead still depends on a kernel patch (posted in a followup). This patch
implements a global kernel tracer for sys_open() syscalls. The choice was made to
use this method since userland tracing is slow, cumbersome (have to attach to
every process running), and hard to implement for system-wide tracing (we don't
care about which process is doing something). A kernel tracer is extremely
efficient and added bonus is that we can leave the trace in memory until we
actually need to process it.

sreadahead-1.0 can be downloaded from it's google code project page here:

  http://sreadahead.googlecode.com/

Regards,

Auke
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