Re: [PATCH 11/11] Do not compact within a preferred zone after acompaction failure
From: Christoph Lameter
Date: Tue Mar 23 2010 - 14:34:09 EST
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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