Now, compaction algorithm become powerful. Migration scanner traverses whole zone range. So, old threshold for depleted zone which is designed to imitate compaction deferring approach isn't appropriate for current compaction algorithm. If we adhere to current threshold, 1, we can't avoid excessive overhead caused by compaction, because one compaction for low order allocation would be easily successful in any situation. This patch re-implements threshold calculation based on zone size and allocation requested order. We judge whther compaction possibility is depleted or not by number of successful compaction. Roughly, 1/100 of future scanned area should be allocated for high order page during one comaction iteration in order to determine whether zone's compaction possiblity is depleted or not. Below is test result with following setup. Memory is artificially fragmented to make order 3 allocation hard. And, most of pageblocks are changed to unmovable migratetype. System: 512 MB with 32 MB Zram Memory: 25% memory is allocated to make fragmentation and 200 MB is occupied by memory hogger. Most pageblocks are unmovable migratetype. Fragmentation: Successful order 3 allocation candidates may be around 1500 roughly. Allocation attempts: Roughly 3000 order 3 allocation attempts with GFP_NORETRY. This value is determined to saturate allocation success. Test: hogger-frag-unmovable redesign threshold compact_free_scanned 6441095 2235764 compact_isolated 2711081 647701 compact_migrate_scanned 4175464 1697292 compact_stall 2059 2092 compact_success 207 210 pgmigrate_success 1348113 318395 Success: 44 40 Success(N): 90 83 This change results in greatly decreasing compaction overhead when zone's compaction possibility is nearly depleted. But, I should admit that it's not perfect because compaction success rate is decreased. More precise tuning threshold would restore this regression, but, it highly depends on workload so I'm not doing it here. Other test doesn't show any regression. System: 512 MB with 32 MB Zram Memory: 25% memory is allocated to make fragmentation and kernel build is running on background. Most pageblocks are movable migratetype. Fragmentation: Successful order 3 allocation candidates may be around 1500 roughly. Allocation attempts: Roughly 3000 order 3 allocation attempts with GFP_NORETRY. This value is determined to saturate allocation success. Test: build-frag-movable redesign threshold compact_free_scanned 2359553 1461131 compact_isolated 907515 387373 compact_migrate_scanned 3785605 2177090 compact_stall 2195 2157 compact_success 247 225 pgmigrate_success 439739 182366 Success: 43 43 Success(N): 89 90 Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> --- mm/compaction.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 99f533f..63702b3 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -129,19 +129,24 @@ static struct page *pageblock_pfn_to_page(unsigned long start_pfn, /* Do not skip compaction more than 64 times */ #define COMPACT_MAX_FAILED 4 -#define COMPACT_MIN_DEPLETE_THRESHOLD 1UL +#define COMPACT_MIN_DEPLETE_THRESHOLD 4UL #define COMPACT_MIN_SCAN_LIMIT (pageblock_nr_pages) static bool compaction_depleted(struct zone *zone) { - unsigned long threshold; + unsigned long nr_possible; unsigned long success = zone->compact_success; + unsigned long threshold; - /* - * Now, to imitate current compaction deferring approach, - * choose threshold to 1. It will be changed in the future. - */ - threshold = COMPACT_MIN_DEPLETE_THRESHOLD; + nr_possible = zone->managed_pages >> zone->compact_order_failed; + + /* Migration scanner can scans more than 1/4 range of zone */ + nr_possible >>= 2; + + /* We hope to succeed more than 1/100 roughly */ + threshold = nr_possible >> 7; + + threshold = max(threshold, COMPACT_MIN_DEPLETE_THRESHOLD); if (success >= threshold) return false; -- 1.9.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>