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    SubjectRe: [PATCH 1/4] vmscan: simplify shrink_inactive_list()
    On Thu, Apr 15, 2010 at 06:54:16PM +0200, Andi Kleen wrote:
    > > It's a buying-time venture, I'll agree but as both approaches are only
    > > about reducing stack stack they wouldn't be long-term solutions by your
    > > criteria. What do you suggest?
    > (from easy to more complicated):
    > - Disable direct reclaim with 4K stacks

    Do not like. While I can see why 4K stacks are a serious problem, I'd
    sooner see 4K stacks disabled than have the kernel behave so differently
    for direct reclaim. It's be tricky to spot regressions in reclaim that
    were due to this .config option

    > - Do direct reclaim only on separate stacks

    This is looking more and more attractive.

    > - Add interrupt stacks to any 8K stack architectures.

    This is a similar but separate problem. It's similar in that interrupt
    stacks can splice subsystems together in terms of stack usage.

    > - Get rid of 4K stacks completely

    Why would we *not* do this? I can't remember the original reasoning
    behind 4K stacks but am guessing it helped fork-orientated workloads in
    startup times in the days before lumpy reclaim and better fragmentation

    Who typically enables this option?

    > - Think about any other stackings that could give large scale recursion
    > and find ways to run them on separate stacks too.

    The patch series I threw up about reducing stack was a cut-down
    approach. Instead of using separate stacks, keep the stack usage out of
    the main caller path where possible.

    > - Long term: maybe we need 16K stacks at some point, depending on how
    > good the VM gets. Alternative would be to stop making Linux more complicated,
    > but that's unlikely to happen.

    Make this Plan D if nothing else works out and we still hit a wall?

    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab

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