Re: Fragments in Ext2 fs

Eric Youngdale (
Wed, 19 Jul 1995 12:40:29 -0400

> Have you checked to make sure that the clustering is really working
> in the 1K cases? Larry McVoy told me some time ago when I talked to
> him about this subject that he had added a system call to use to
> check to see if any clustering was happening, and he didn't see a
> single instance of it actually happening.
>Hmmm. I must admit that I just assumed that the clustering patches were
>doing their job as they've been in the kernel for quite a long time now.
>I'll have to read over the clustering code enough to understand how it
works >and run some further tests.

I find it hard to believe that they are not doing the job - the
performance would really suck if this were the case. Do you happen to know
exactly what it was that Larry was counting? When I have looked at things
from the scsi end of things, it seemed to be working correctly.

Are you testing reads, writes, or both?

My guess is that there is some overhead in setting up and
working with the additional buffer headers that you have with 1K blocksizes.

I think the buffer cache code is due for a complete rewrite, but it
gets a bit tricky as there are lots of considerations.


"The woods are lovely, dark and deep.  But I have promises to keep,
And lines to code before I sleep, And lines to code before I sleep."