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    SubjectRe: [PATCH 12/12] vmscan: Do not writeback pages in direct reclaim
    On Tue, 15 Jun 2010 20:29:49 -0400
    Rik van Riel <riel@redhat.com> wrote:

    > On 06/15/2010 08:17 PM, KAMEZAWA Hiroyuki wrote:
    > > On Tue, 15 Jun 2010 15:16:01 +0100
    > > Mel Gorman<mel@csn.ul.ie> wrote:
    >
    > >> But in turn, where is mem_cgroup_hierarchical_reclaim called from direct
    > >> reclaim? It appears to be only called from the fault path or as a result
    > >> of the memcg changing size.
    > >>
    > > yes. It's only called from
    > > - page fault
    > > - add_to_page_cache()
    > >
    > > I think we'll see no stack problem. Now, memcg doesn't wakeup kswapd for
    > > reclaiming memory, it needs direct writeback.
    >
    > Of course, a memcg page fault could still be triggered
    > from copy_to_user or copy_from_user, with a fairly
    > arbitrary stack frame above...
    >

    Hmm. But I don't expect copy_from/to_user is called in very deep stack.

    Should I prepare a thread for reclaiming memcg pages ?
    Because we shouldn't limit kswapd's cpu time by CFS cgroup, waking up
    kswapd just because "a memcg hit limits" isn't fun.

    Hmm, or do you recommend no-dirty-page-writeback when a memcg hits limit ?
    Maybe we'll see much swaps.

    I want to go with this for a while, changing memcg's behavior will took
    some amounts of time, there are only a few developpers.

    Thanks,
    -Kame



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