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SubjectRe: Request: I/O request recording
Andrew Morton wrote:
> You could certainly do that. Given disk block #N you need to search all
> files on the disk asking "who owns this block". The FIBMAP ioctl can be
> used on most filesystems (ext2, ext3, others..) to find out which blocks a
> file is using. See bmap.c in
>
> http://www.zip.com.au/~akpm/linux/patches/stuff/ext3-tools.tar.gz
>
> Unfortunately you cannot determine a directory's blocks in this way.
> Ext3's directories live in the /dev/hda1 pagecache anyway. ext2's
> directories each have their own pagecache.

OK, I've written something that does this (but only correctly for ext3).
I've put it here:

http://www.xs4all.nl/~bsamwel/bootup_prefetch.tar.gz

I haven't had the opportunity to do good measurements, so I don't really
know if it even increases performance. If anyone feels like benchmarking
this, I'd be very happy to hear from you. I don't really expect
performance increases, as the bootup scripts seem to have enough
processing to do to keep the system busy even without disk I/O. I wonder
if it might make a difference on a faster processor though, my system's
kind of sluggish by today's standards.

-- Bart
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