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    SubjectRe: [PATCH 02/12] mm: supporting variables and functions for balanced zone aging
    Marcelo Tosatti <> wrote:
    > Hi Andrew,
    > On Thu, Dec 01, 2005 at 02:37:14AM -0800, Andrew Morton wrote:
    > > Wu Fengguang <> wrote:
    > > >
    > > > The zone aging rates are currently imbalanced,
    > >
    > > ZONE_DMA is out of whack. It shouldn't be, and I'm not aware of anyone
    > > getting in and working out why. I certainly wouldn't want to go and add
    > > all this stuff without having a good understanding of _why_ it's out of
    > > whack. Perhaps it's just some silly bug, like the thing I pointed at in
    > > the previous email.
    > I think that the problem is caused by the interaction between
    > the way reclaiming is quantified and parallel allocators.

    Could be. But what about the bug which I think is there? That'll cause
    overscanning of the DMA zone.

    > The zones have different sizes, and each zone reclaim iteration
    > scans the same number of pages. It is unfair.

    Nope. See how shrink_zone() bases nr_active and nr_inactive on
    zone->nr_active and zone_nr_inactive. These calculations are intended to
    cause the number of scanned pages in each zone to be

    (zone->nr-active + zone->nr_inactive) >> sc->priority.

    > On top of that, kswapd is likely to block while doing its job,
    > which means that allocators have a chance to run.

    kswapd should only block under rare circumstances - huge amounts of dirty
    pages coming off the tail of the LRU.

    > --- mm/vmscan.c.orig 2006-01-01 12:44:39.000000000 -0200
    > +++ mm/vmscan.c 2006-01-01 16:43:54.000000000 -0200
    > @@ -616,8 +616,12 @@
    > {

    Please use `diff -p'.

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