Re: How git affects kernel.org performance

On Sun, Jan 07, 2007 at 12:58:38AM -0800, H. Peter Anvin wrote:

Willy Tarreau wrote:

quoted

At work, we had the same problem on a file server with ext3. We use rsync
to make backups to a local IDE disk, and we noticed that getdents() took
about the same time as Peter reports (0.2 to 2 seconds), especially in
maildir directories. We tried many things to fix it with no result,
including enabling dirindexes. Finally, we made a full backup, and switched
over to XFS and the problem totally disappeared. So it seems that the
filesystem matters a lot here when there are lots of entries in a
directory, and that ext3 is not suitable for usages with thousands
of entries in directories with millions of files on disk. I'm not
certain it would be that easy to try other filesystems on kernel.org
though :-/

Changing filesystems would mean about a week of downtime for a server. 
It's painful, but it's doable; however, if we get a traffic spike during 
that time it'll hurt like hell.

However, if there is credible reasons to believe XFS will help, I'd be 
inclined to try it out.

The problem is that I have no sufficient FS knowledge to argument why
it helps here. It was a desperate attempt to fix the problem for us
and it definitely worked well.

Hmmm I'm thinking about something very dirty : would it be possible
to reduce the current FS size to get more space to create another
FS ? Supposing you create a XX GB/TB XFS after the current ext3,
you would be able to mount it in some directories with --bind and
slowly switch some parts to it. The problem with this approach is
that it will never be 100% converted, but as an experiment it might
be worth it, no ?

Willy