From: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Subject: mm, compaction: always finish scanning of a full pageblock When compaction is finishing, it uses a flag to ensure the pageblock is complete but it makes sense to always complete migration of a pageblock. Minimally, skip information is based on a pageblock and partially scanned pageblocks may incur more scanning in the future. The pageblock skip handling also becomes more strict later in the series and the hint is more useful if a complete pageblock was always scanned. The potentially impacts latency as more scanning is done but it's not a consistent win or loss as the scanning is not always a high percentage of the pageblock and sometimes it is offset by future reductions in scanning. Hence, the results are not presented this time due to a misleading mix of gains/losses without any clear pattern. However, full scanning of the pageblock is important for later patches. Link: http://lkml.kernel.org/r/20190118175136.31341-8-mgorman@xxxxxxxxxxxxxxxxxxx Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: YueHaibing <yuehaibing@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/compaction.c | 19 ++++++++----------- mm/internal.h | 1 - 2 files changed, 8 insertions(+), 12 deletions(-) --- a/mm/compaction.c~mm-compaction-always-finish-scanning-of-a-full-pageblock +++ a/mm/compaction.c @@ -1331,16 +1331,14 @@ static enum compact_result __compact_fin if (is_via_compact_memory(cc->order)) return COMPACT_CONTINUE; - if (cc->finishing_block) { - /* - * We have finished the pageblock, but better check again that - * we really succeeded. - */ - if (IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages)) - cc->finishing_block = false; - else - return COMPACT_CONTINUE; - } + /* + * Always finish scanning a pageblock to reduce the possibility of + * fallbacks in the future. This is particularly important when + * migration source is unmovable/reclaimable but it's not worth + * special casing. + */ + if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages)) + return COMPACT_CONTINUE; /* Direct compactor: Is a suitable page free? */ for (order = cc->order; order < MAX_ORDER; order++) { @@ -1382,7 +1380,6 @@ static enum compact_result __compact_fin return COMPACT_SUCCESS; } - cc->finishing_block = true; return COMPACT_CONTINUE; } } --- a/mm/internal.h~mm-compaction-always-finish-scanning-of-a-full-pageblock +++ a/mm/internal.h @@ -203,7 +203,6 @@ struct compact_control { bool direct_compaction; /* False from kcompactd or /proc/... */ bool whole_zone; /* Whole zone should/has been scanned */ bool contended; /* Signal lock or sched contention */ - bool finishing_block; /* Finishing current pageblock */ }; unsigned long _
