Re: [patch][rfc][rft] vm throughput 2.4.2-ac4

From: Mike Galbraith (
Date: Wed Feb 28 2001 - 00:04:12 EST

On Tue, 27 Feb 2001, Marcelo Tosatti wrote:

> On Tue, 27 Feb 2001, Mike Galbraith wrote:
> > What the patch does is simply to push I/O as fast as we can.. we're
> > by definition I/O bound and _can't_ defer it under any circumstance,
> > for in this direction lies constipation. The only thing in the world
> > which will make it better is pushing I/O.
> In your I/O bound case, yes. But not in all cases.

That's one reason I tossed it out. I don't _think_ it should have any
negative effect on other loads, but a test run might find otherwise.

> > What we do right now (as kswapd) is scan a tiny portion of the active
> > page list, and then push an arbitrary amount of swap because we can't
> > possibly deactivate enough pages if our shortage is larger than the
> > search area (nr_active_pages >> 6).. repeat until give-up time. In
> > practice here (test load, but still..), that leads to pushing soon
> > to be unneeded [supposition!] pages into swap a full 3/4 of the time.

(correction: it's 2/3 of the time not 3/4.. off by one bug in fingers;)

> Have you tried to use SWAP_SHIFT as 4 instead of 5 on a stock 2.4.2-ac5 to
> see if the system still swaps out too much?

Not yet, but will do.


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