Re: [SLUG] 2.4 VM is broken

From: Derek Glidden (
Date: Thu Jun 07 2001 - 11:35:52 EDT

Paul M Foster wrote:
> On Wed, Jun 06, 2001 at 12:23:02PM -0400, Derek Glidden wrote:
> >
> > I've kicked up a bit of an ant's nest on LKML about the state of VM/swap
> > under 2.4. If you were at the dinner with Maddog, I ranted about this
> > for a bit and you might remember some of the problems. I finally sat
> > down to do some actual tests against the 2.4 VM subsystem and came up
> > with some really ridiculous results. You might find this interesting
> > reading. (and then again, you may not...)
> >
> >
> >
> What's most interesting to me is the attitude you mentioned: "Oh, then
> just get more swap!". I paged through all the messages in this thread,

The thing that really got me and why I made that comment to begin with
is that the steps I outlined really had nothing to do with the amount of
swap on the machine at all. The problem has to do with the kernel's
ability to recover pages from swap once they've been swapped out and how
badly it affects performance. A lot of the people who responded
obviously didn't even read the original message and just saw "swap" and
immediately gave the party-line answer of "you need more swap."

> and I'm amazed at the lack of substantive, helpful, realistic comment on
> the issue. Even Alan Cox just added more noise. To be fair, someone
> posted a patch, and there were a couple of other helpful emails. But for
> the most part, it was bickering based on misunderstanding. And someone

I was amazed at Alan's response. I've had a few direct emails from him
before on various issues and he's always been level-headed and sane. I
think this whole "VM uses too much swap" thing has really gotten
everyone's panties in a wad and nobody has a very clear head about
anything related to VM anymore. I can't wait until it's all cleared up.

I think I've also learned that the people making the most noise are
doing the least work on this problem.

> even characterized the 2.4 kernel as unstable branch. Ahem? I thought
> that's what the odd numbered (2.3, 2.5) were supposed to be.

Supposedly, yes. :)

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