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    SubjectRe: [PATCH -mm] throttle direct reclaim when too many pages are isolated already
    On Wed, 15 Jul 2009 23:42:28 -0400 Rik van Riel <riel@redhat.com> wrote:

    > Andrew Morton wrote:
    > > On Wed, 15 Jul 2009 23:28:14 -0400 Rik van Riel <riel@redhat.com> wrote:
    >
    > >> If we are stuck at this point in the page reclaim code,
    > >> it is because too many other tasks are reclaiming pages.
    > >>
    > >> That makes it fairly safe to just return SWAP_CLUSTER_MAX
    > >> here and hope that __alloc_pages() can get a page.
    > >>
    > >> After all, if __alloc_pages() thinks it made progress,
    > >> but still cannot make the allocation, it will call the
    > >> pageout code again.
    > >
    > > Which will immediately return because the caller still has
    > > fatal_signal_pending()?
    >
    > Other processes are in the middle of freeing pages at
    > this point, so we should succeed in __alloc_pages()
    > fairly quickly (and then die and free all our memory).

    What if it's a uniprocessor machine and all those processes are
    scheduled out? We sit there chewing 100% CPU and not doing anything
    afaict.

    Even if it _is_ SMP, we could still chew decent-sized blips of CPU time
    rattling around waiting for something to happen.


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