Re: [PATCH] Prefaulting

From: Arjan van de Ven
Date: Sat Mar 12 2005 - 04:12:00 EST

> >From a quick peek it seems that the patch makes negligible difference for a
> kernel compilation when prefaulting 1-2 pages and slows the workload down
> quite a lot when prefaulting up to 16 pages.

well the last time I saw prefaulting experiments (Ingo was involved
iirc) the problem was that the hitrate for the prefaults was such that
the costs for tearing down the extra redundant rmap chains was more
expensive than taking the "extra" faults. It seems linux has pretty
cheap faulting logic invalidating some of traditional OS assumptions...

(fwiw one of the worst tests I remember was doing a lot of very short
shell script executions; the case where bash lives briefly so that you
get maximum cost for the extra teardowns while not a lot of bash gets
run so prefaulting doesn't make a lot of difference)

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