[ANNOUNCE] sreadahead-1.0

From: Kok, Auke
Date: Tue Jan 27 2009 - 15:07:17 EST


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:



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