Self fragmentation? (Was: Re: Parallel Startup for KDE.)

[Andrew Morton]

Roger Larsson <roger.larsson at norran.net> wrote:
>
> >
> > We don't really have a fix for that.  It's surprisingly bad for an ext2
> > filesystem.
> 
> Can we be sure about that? Server use != KDE (konqueror, kmail),
> KDE compilations running for days in background, ...

ext2 will deteriorate over time.  But what *really* hurts it is
slowly-growing files.  mboxes.  They end up splattered all over the disk. 
ANd when you remove them you end up with holes splattered all over the
disk.

> >
> > I usually keep a spare partition around, do a `cp -a' and swizzle the
> > mountpoints.
> >
> 
> So I did a little experiment (took a tar copy too...)
> # cp -a ~/.kde other_disk/roger.kde
> # rm -r ~/.kde
> # cp -a other_disk/roger.kde ~/.kde
> 
> And retested, kmailrc to uses two blocks.

OK.

> Will ext2 prefere that all files in a directory end up in the same blockgroup?

Yes.

> How is data blocks pages reused?

Complex.  Usually it ends up first-fit inside a blockgroup, but 2.6 adds
some coloring to the starting offset in the blockgroup for the search.

> What will happen over time with lots of small files, few big, files are 
> rewritten (growing) by writing completely new file, rename...

It turns to crap...