From: Vlastimil Babka <vbabka@xxxxxxx> Subject: mm, compaction: extend pageblock_skip_persistent() to all compound pages pageblock_skip_persistent() checks for HugeTLB pages of pageblock order. When clearing pageblock skip bits for compaction, the bits are not cleared for such pageblocks, because they cannot contain base pages suitable for migration, nor free pages to use as migration targets. This optimization can be simply extended to all compound pages of order equal or larger than pageblock order, because migrating such pages (if they support it) cannot help sub-pageblock fragmentation. This includes THP's and also gigantic HugeTLB pages, which the current implementation doesn't persistently skip due to a strict pageblock_order equality check and not recognizing tail pages. While THP pages are generally less "persistent" than HugeTLB, we can still expect that if a THP exists at the point of __reset_isolation_suitable(), it will exist also during the subsequent compaction run. The time difference here could be actually smaller than between a compaction run that sets a (non-persistent) skip bit on a THP, and the next compaction run that observes it. Link: http://lkml.kernel.org/r/20171102121706.21504-1-vbabka@xxxxxxx Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx> Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/compaction.c | 25 ++++++++++++++----------- 1 file changed, 14 insertions(+), 11 deletions(-) diff -puN mm/compaction.c~mm-compaction-extend-pageblock_skip_persistent-to-all-compound-pages mm/compaction.c --- a/mm/compaction.c~mm-compaction-extend-pageblock_skip_persistent-to-all-compound-pages +++ a/mm/compaction.c @@ -219,17 +219,21 @@ static void reset_cached_positions(struc } /* - * Hugetlbfs pages should consistenly be skipped until updated by the hugetlb - * subsystem. It is always pointless to compact pages of pageblock_order and - * the free scanner can reconsider when no longer huge. + * Compound pages of >= pageblock_order should consistenly be skipped until + * released. It is always pointless to compact pages of such order (if they are + * migratable), and the pageblocks they occupy cannot contain any free pages. */ -static bool pageblock_skip_persistent(struct page *page, unsigned int order) +static bool pageblock_skip_persistent(struct page *page) { - if (!PageHuge(page)) + if (!PageCompound(page)) return false; - if (order != pageblock_order) - return false; - return true; + + page = compound_head(page); + + if (compound_order(page) >= pageblock_order) + return true; + + return false; } /* @@ -256,7 +260,7 @@ static void __reset_isolation_suitable(s continue; if (zone != page_zone(page)) continue; - if (pageblock_skip_persistent(page, compound_order(page))) + if (pageblock_skip_persistent(page)) continue; clear_pageblock_skip(page); @@ -323,8 +327,7 @@ static inline bool isolation_suitable(st return true; } -static inline bool pageblock_skip_persistent(struct page *page, - unsigned int order) +static inline bool pageblock_skip_persistent(struct page *page) { return false; } _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
