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    SubjectRe: memcg writeout throttling, was: [patch 4/4] memcg: use native word page statistics counters
    On Mon, Nov 08, 2010 at 09:07:35AM +0900, Minchan Kim wrote:
    > BTW, let me ask a question.
    > dirty_writeback_pages seems to be depends on mem_cgroup_page_stat's
    > result(ie, negative) for separate global and memcg.
    > But mem_cgroup_page_stat could return negative value by per-cpu as
    > well as root cgroup.
    > If I understand right, Isn't it a problem?

    Yes, the numbers are not reliable and may be off by some. It appears
    to me that the only sensible interpretation of a negative sum is to
    assume zero, though. So to be honest, I don't understand the fallback
    to global state when the local state fluctuates around low values.

    This function is also only used in throttle_vm_writeout(), where the
    outcome is compared to the global dirty threshold. So using the
    number of writeback pages _from the current cgroup_ and falling back
    to global writeback pages when this number is low makes no sense to me
    at all.

    I looks like it should rather compare the cgroup state with the cgroup
    limit, and the global state with the global limit.

    Can somebody explain the reasoning behind this? And in case it makes
    sense after all, put a comment into this function?


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      Last update: 2010-11-08 10:41    [W:0.018 / U:6.536 seconds]
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