Re: adventures in booting

[David Zeuthen <david fubar dk>]

On Thu, 2004-12-02 at 12:59 -0500, Colin Walters wrote:
> On Thu, 2004-12-02 at 12:40 -0500, David Zeuthen wrote:
> 
> > I'm almost positive it requires kernel changes to do this the right way;
> > one naive idea is to have a userspace daemon, capturing what blocks are
> > read when (kernel tells this daemon using the kernel events layer). This
> > would run in the first three minutes on each and every boot. When the
> > system is idle (and only when running on AC power!) another daemon
> > rearranges blocks on the disk. What blocks to rearrange could be the
> > result of a computation involving several three-minute result sets.
> 
> Rearranging sounds complex and dangerous, since it requires deep
> integration with the filesystem.  The online resizing took quite a long
> time to appear and that is conceptually much simpler.  Why not do it on
> the block device layer (without knowledge of the filesystem) and just
> copy those blocks to a reserved area of the block device?  Disks are
> big, duplicating say 100MB for this purpose wouldn't be bad.  We would
> need to ensure that mkfs.ext3 would leave enough space for this though
> (and probably whatever does the copying would have to make sure that the
> filesystem wasn't in the way; perhaps an ext flag).
> 

This sounds much simpler and better; for good measure, ensure that the
reserved area is in the beginning of the partition as reads are
generally faster on lower sectors. This article seems to suggest

 http://www.kernelthread.com/mac/apme/optimizations/

that Mac OS X is doing something that like although it appears to be on
a file system level rather than a block level. The concept of "hot
files" is interesting.

Cheers,
David

>