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    SubjectRe: [PATCH] mm: yield during swap prefetching
    On Thu, 9 Mar 2006 01:22 pm, Nick Piggin wrote:
    > Pavel Machek wrote:
    > >On Út 07-03-06 16:05:15, Andrew Morton wrote:
    > >>Why do you want that?
    > >>
    > >>If prefetch is doing its job then it will save the machine from a pile of
    > >>major faults in the near future. The fact that the machine happens
    > >
    > >Or maybe not.... it is prefetch, it may prefetch wrongly, and you
    > >definitely want it doing nothing when system is loaded.... It only
    > >makes sense to prefetch when system is idle.
    > Right. Prefetching is obviously going to have a very low work/benefit,
    > assuming your page reclaim is working properly, because a) it doesn't
    > deal with file pages, and b) it is doing work to reclaim pages that
    > have already been deemed to be the least important.
    > What it is good for is working around our interesting VM that apparently
    > allows updatedb to swap everything out (although I haven't seen this
    > problem myself), and artificial memory hogs. By moving work to times of
    > low cost. No problem with the theory behind it.
    > So as much as a major fault costs in terms of performance, the tiny
    > chance that prefetching will avoid it means even the CPU usage is
    > questionable. Using sched_yield() seems like a hack though.

    Yeah it's a hack alright. Funny how at last I find a place where yield does
    exactly what I want and because we hate yield so much noone wants me to use
    it all.

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