On 1/4/19 1:50 PM, Mel Gorman wrote: > When scanning for sources or targets, PageCompound is checked for huge > pages as they can be skipped quickly but it happens relatively late after > a lot of setup and checking. This patch short-cuts the check to make it > earlier. It might still change when the lock is acquired but this has > less overhead overall. The free scanner advances but the migration scanner > does not. Typically the free scanner encounters more movable blocks that > change state over the lifetime of the system and also tends to scan more > aggressively as it's actively filling its portion of the physical address > space with data. This could change in the future but for the moment, > this worked better in practice and incurred fewer scan restarts. > > The impact on latency and allocation success rates is marginal but the > free scan rates are reduced by 32% and system CPU usage is reduced by > 2.6%. The 2-socket results are not materially different.
Hmm, interesting that adjusting migrate scanner affected free scanner. Oh well. > Signed-off-by: Mel Gorman <[email protected]> Acked-by: Vlastimil Babka <[email protected]> Nit below. > --- > mm/compaction.c | 16 ++++++++++++---- > 1 file changed, 12 insertions(+), 4 deletions(-) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 608d274f9880..921720f7a416 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1071,6 +1071,9 @@ static bool suitable_migration_source(struct > compact_control *cc, > { > int block_mt; > > + if (pageblock_skip_persistent(page)) > + return false; > + > if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction) > return true; > > @@ -1693,12 +1696,17 @@ static isolate_migrate_t isolate_migratepages(struct > zone *zone, > continue; > > /* > - * For async compaction, also only scan in MOVABLE blocks. > - * Async compaction is optimistic to see if the minimum amount > - * of work satisfies the allocation. > + * For async compaction, also only scan in MOVABLE blocks > + * without huge pages. Async compaction is optimistic to see > + * if the minimum amount of work satisfies the allocation. > + * The cached PFN is updated as it's possible that all > + * remaining blocks between source and target are suitable ^ unsuitable? > + * and the compaction scanners fail to meet. > */ > - if (!suitable_migration_source(cc, page)) > + if (!suitable_migration_source(cc, page)) { > + update_cached_migrate(cc, block_end_pfn); > continue; > + } > > /* Perform the isolation */ > low_pfn = isolate_migratepages_block(cc, low_pfn, >
