Re: [PATCH] kswapd fix & logic improvement

[Rik van Riel <H.H.vanRiel@fys.ruu.nl>]

On Tue, 3 Mar 1998, Michael L. Galbraith wrote:

> > To 'recover from' or 'handle' your attack (180+ mb working
> > set on an 80 mb machine) is going to need 'real' swapping,
> > ie. the temporary suspension of processes to reduce VM load.
> 
> I've run much larger working sets on this machine without either
> losing control or having the tasks killed. I've run simulations
> which ate 400+ Mb. The realtime aspect was a joke, but it worked.

When allocation is done piece-by-piece, and there's only
one big process which is faulting all the time, all known
Linux kernels can handle it (more or less).

> > This patch is only an improvement for normal use. Anyways,
> > thrashing can't be combatted by paging algorithms, no matter
> > how good.
> 
> OK.. thought you wanted it pounded upon.

You were right about that. I wanted to be sure that my
patch was at least as solid as the old code before it
gets merged into the kernel. Judging from the reports
I got, it is. In fact, most people have reported a big
improvement, and some people have pounded and ground it
to a crawl (without being able to make it crash).

> It was running fine with all tasks being scheduled smoothly until
> something triggered a mega-thrash.

Once you start thrashing, only real swapping is an option
to save performance (somewhat).

> > I'll be working on the swapping daemon as soon as I've got
> > the current patch sorted out...
> 
> Turned out the kswapd messages weren't related to the thrashing.
> I would have seen it if I hadn't jumped straight into X.

Ahh, yes. X allocates a _lot_ of memory at once, and then
the damn thing _uses_ it at once... This is guaranteed to
make kswapd a bit nervous, both with or without my patch.

Rik.
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