On Tue 06-09-16 15:52:57, Vlastimil Babka wrote:
> The new ultimate compaction priority disables some heuristics, which may result
> in excessive cost. This is fine for non-costly orders where we want to try hard
> before resulting for OOM, but might be disruptive for costly orders which do
> not trigger OOM and should generally have some fallback. Thus, we disable the
> full priority for costly orders.
>
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> include/linux/compaction.h | 1 +
> mm/page_alloc.c | 5 ++++-
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 585d55cb0dc0..0d8415820fc3 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -9,6 +9,7 @@ enum compact_priority {
> COMPACT_PRIO_SYNC_FULL,
> MIN_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_FULL,
> COMPACT_PRIO_SYNC_LIGHT,
> + MIN_COMPACT_COSTLY_PRIORITY = COMPACT_PRIO_SYNC_LIGHT,
> DEF_COMPACT_PRIORITY = COMPACT_PRIO_SYNC_LIGHT,
> COMPACT_PRIO_ASYNC,
> INIT_COMPACT_PRIORITY = COMPACT_PRIO_ASYNC
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f8bed910e3cf..ff60a2837c58 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3165,6 +3165,7 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
> int compaction_retries)
> {
> int max_retries = MAX_COMPACT_RETRIES;
> + int min_priority;
>
> if (!order)
> return false;
> @@ -3204,7 +3205,9 @@ should_compact_retry(struct alloc_context *ac, int order, int alloc_flags,
> * if we exhausted all retries at the lower priorities
> */
> check_priority:
> - if (*compact_priority > MIN_COMPACT_PRIORITY) {
> + min_priority = (order > PAGE_ALLOC_COSTLY_ORDER) ?
> + MIN_COMPACT_COSTLY_PRIORITY : MIN_COMPACT_PRIORITY;
> + if (*compact_priority > min_priority) {
> (*compact_priority)--;
> return true;
> }
> --
> 2.9.3
--
Michal Hocko
SUSE Labs
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