>
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> Compaction can provide a wild variation of feedback to the caller. Many
> of them are implementation specific and the caller of the compaction
> (especially the page allocator) shouldn't be bound to specifics of the
> current implementation.
>
> This patch abstracts the feedback into three basic types:
> - compaction_made_progress - compaction was active and made some
> progress.
> - compaction_failed - compaction failed and further attempts to
> invoke it would most probably fail and therefore it is not
> worth retrying
> - compaction_withdrawn - compaction wasn't invoked for an
> implementation specific reasons. In the current implementation
> it means that the compaction was deferred, contended or the
> page scanners met too early without any progress. Retrying is
> still worthwhile.
>
> [vbabka@xxxxxxx: do not change thp back off behavior]
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
> include/linux/compaction.h | 79 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 79 insertions(+)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index a7b9091ff349..a002ca55c513 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -78,6 +78,70 @@ extern void compaction_defer_reset(struct zone *zone, int order,
> bool alloc_success);
> extern bool compaction_restarting(struct zone *zone, int order);
>
> +/* Compaction has made some progress and retrying makes sense */
> +static inline bool compaction_made_progress(enum compact_result result)
> +{
> + /*
> + * Even though this might sound confusing this in fact tells us
> + * that the compaction successfully isolated and migrated some
> + * pageblocks.
> + */
> + if (result == COMPACT_PARTIAL)
> + return true;
> +
> + return false;
> +}
> +
> +/* Compaction has failed and it doesn't make much sense to keep retrying. */
> +static inline bool compaction_failed(enum compact_result result)
> +{
> + /* All zones where scanned completely and still not result. */
s/where/were/
> + if (result == COMPACT_COMPLETE)
> + return true;
> +
> + return false;
> +}
> +
> +/*
> + * Compaction has backed off for some reason. It might be throttling or
> + * lock contention. Retrying is still worthwhile.
> + */
> +static inline bool compaction_withdrawn(enum compact_result result)
> +{
> + /*
> + * Compaction backed off due to watermark checks for order-0
> + * so the regular reclaim has to try harder and reclaim something.
> + */
> + if (result == COMPACT_SKIPPED)
> + return true;
> +
> + /*
> + * If compaction is deferred for high-order allocations, it is
> + * because sync compaction recently failed. If this is the case
> + * and the caller requested a THP allocation, we do not want
> + * to heavily disrupt the system, so we fail the allocation
> + * instead of entering direct reclaim.
> + */
> + if (result == COMPACT_DEFERRED)
> + return true;
> +
> + /*
> + * If compaction in async mode encounters contention or blocks higher
> + * priority task we back off early rather than cause stalls.
> + */
> + if (result == COMPACT_CONTENDED)
> + return true;
> +
> + /*
> + * Page scanners have met but we haven't scanned full zones so this
> + * is a back off in fact.
> + */
> + if (result == COMPACT_PARTIAL_SKIPPED)
> + return true;
> +
> + return false;
> +}
> +
> extern int kcompactd_run(int nid);
> extern void kcompactd_stop(int nid);
> extern void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx);
> @@ -114,6 +178,21 @@ static inline bool compaction_deferred(struct zone *zone, int order)
> return true;
> }
>
> +static inline bool compaction_made_progress(enum compact_result result)
> +{
> + return false;
> +}
> +
> +static inline bool compaction_failed(enum compact_result result)
> +{
> + return false;
> +}
> +
> +static inline bool compaction_withdrawn(enum compact_result result)
> +{
> + return true;
> +}
> +
> static inline int kcompactd_run(int nid)
> {
> return 0;
> --
> 2.8.0.rc3
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