Re: 2.1.131 first impressions

Rik van Riel (
Mon, 7 Dec 1998 13:02:04 +0100 (CET)

On Mon, 7 Dec 1998, Jamie Lokier wrote:

> I've just switched from 2.1.129 to 2.1.131 + Rik's "fastest VM system"
> patch, and I have to say, nice!
> Disk activity
> =============
> Something's changed. Can't say whether it's the main tree changes or
> Rik's mm changes (I haven't tried plain 2.1.131).

Both. Stephen's changes to shrink_mmap() really have a huge
influence on performance.

> I'm not using any swap either (well, 16k on a 64MB system). It feels
> faster somehow anyway.

The not-using-any-swap part comes both from Stephen's improvement
and my change to vmscan.c; we now quit a swap_out() loop earlier
and we do (over?-)agressive pruning of the page and buffer caches.

> Well, apart from Squid which still spends a few minutes grinding
> away at the disk when it starts. I would like to find a way to fix
> this, it's probably the most thrashy thing my disk has to handle and
> it does slow down everything else for a while quite significantly.

This could be a side effect of a too agressive pruning of the
caches. We should fix this.

> Netscape still hits the disk very hard when it starts, and takes what
> seems like just as long. Netscape is pretty quick to start the second
> time though (about 3 seconds), so it's definitely a paging thing. Is
> there anything which could be done with paging
> read-ahead/read-behind/read-cleverer to make Netscape not thrash the
> disk when it starts?

No, not really. When Netscape starts it is not in cache yet :)

I agree that we should do better readbehind though. I am
currently designing a nice algorithm for deciding whether
to do read-ahead, read-behind, a bit of both or a lot of
both. It is mainly focused at swap I/O though...

File I/O might be better served with a slightly different
algorithm, so we need a volunteer for that... If you are
that volunteer: is the list to be.


Rik -- the flu hits, the flu hits, the flu hits -- MORE
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