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    SubjectRe: [PATCH 1/3] mm: vmscan: Do use use PF_SWAPWRITE from zone_reclaim
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    Hi KOSAKi,

    On Tue, Jul 12, 2011 at 6:40 PM, KOSAKI Motohiro
    <kosaki.motohiro@jp.fujitsu.com> wrote:
    > (2011/07/12 18:27), Minchan Kim wrote:
    >> Hi Mel,
    >>
    >> On Mon, Jul 11, 2011 at 10:01 PM, Mel Gorman <mgorman@suse.de> wrote:
    >>> Zone reclaim is similar to direct reclaim in a number of respects.
    >>> PF_SWAPWRITE is used by kswapd to avoid a write-congestion check
    >>> but it's set also set for zone_reclaim which is inappropriate.
    >>> Setting it potentially allows zone_reclaim users to cause large IO
    >>> stalls which is worse than remote memory accesses.
    >>
    >> As I read zone_reclaim_mode in vm.txt, I think it's intentional.
    >> It has meaning of throttle the process which are writing large amounts
    >> of data. The point is to prevent use of remote node's free memory.
    >>
    >> And we has still the comment. If you're right, you should remove comment.
    >> "         * and we also need to be able to write out pages for RECLAIM_WRITE
    >>          * and RECLAIM_SWAP."
    >>
    >>
    >> And at least, we should Cc Christoph and KOSAKI.
    >
    > Of course, I'll take full ack this. Do you remember I posted the same patch
    > about one year ago. At that time, Mel disagreed me and I'm glad to see he changed
    > the mind. :)


    I remember that but I don't know why Mel didn't ack at that time.
    http://lkml.org/lkml/2010/8/5/44

    Anyway, Hannes's bd2f6199cf is to introduce lumpy reclaim of
    zone_reclaim so it's natural to increase latency for getting big order
    pages(ie, it's a trade-off).

    And as I read about zone_reclaim_mode in Documentation/sysctl/vm.txt,
    I think big latency(ie, throttling of the process) is intentional to
    prevent stealing pages for other nodes.

    If I am not against this patch, at least, we need agreement of
    Christoph and others and if we agree this change, we changes vm.txt,
    too.


    --
    Kind regards,
    Minchan Kim
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