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    SubjectRe: [PATCH 11/11] Do not compact within a preferred zone after a compaction failure
    On Tue, 23 Mar 2010, Mel Gorman wrote:

    > The fragmentation index may indicate that a failure it due to external

    s/it/is/

    > fragmentation, a compaction run complete and an allocation failure still

    ???

    > fail. There are two obvious reasons as to why
    >
    > o Page migration cannot move all pages so fragmentation remains
    > o A suitable page may exist but watermarks are not met
    >
    > In the event of compaction and allocation failure, this patch prevents
    > compaction happening for a short interval. It's only recorded on the

    compaction is "recorded"? deferred?

    > preferred zone but that should be enough coverage. This could have been
    > implemented similar to the zonelist_cache but the increased size of the
    > zonelist did not appear to be justified.

    > @@ -1787,6 +1787,9 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
    > */
    > count_vm_event(COMPACTFAIL);
    >
    > + /* On failure, avoid compaction for a short time. */
    > + defer_compaction(preferred_zone, jiffies + HZ/50);
    > +

    20ms? How was that interval determined?



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