From: Zi Yan <ziy@xxxxxxxxxx> migrate_pages() supports >0 order folio migration and during compaction, even if compaction_alloc() cannot provide >0 order free pages, migrate_pages() can split the source page and try to migrate the base pages from the split. It can be a baseline and start point for adding support for compacting >0 order folios. Suggested-by: Huang Ying <ying.huang@xxxxxxxxx> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx> --- mm/compaction.c | 43 +++++++++++++++++++++++++++++++++++-------- 1 file changed, 35 insertions(+), 8 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index 27ada42924d5..61389540e1f1 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -816,6 +816,21 @@ static bool too_many_isolated(struct compact_control *cc) return too_many; } +/* + * 1. if the page order is larger than or equal to target_order (i.e., + * cc->order and when it is not -1 for global compaction), skip it since + * target_order already indicates no free page with larger than target_order + * exists and later migrating it will most likely fail; + * + * 2. compacting > pageblock_order pages does not improve memory fragmentation, + * skip them; + */ +static bool skip_isolation_on_order(int order, int target_order) +{ + return (target_order != -1 && order >= target_order) || + order >= pageblock_order; +} + /** * isolate_migratepages_block() - isolate all migrate-able pages within * a single pageblock @@ -1009,7 +1024,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, /* * Regardless of being on LRU, compound pages such as THP and * hugetlbfs are not to be compacted unless we are attempting - * an allocation much larger than the huge page size (eg CMA). + * an allocation larger than the compound page size. * We can potentially save a lot of iterations if we skip them * at once. The check is racy, but we can consider only valid * values and the only danger is skipping too much. @@ -1017,11 +1032,18 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, if (PageCompound(page) && !cc->alloc_contig) { const unsigned int order = compound_order(page); - if (likely(order <= MAX_PAGE_ORDER)) { - low_pfn += (1UL << order) - 1; - nr_scanned += (1UL << order) - 1; + /* + * Skip based on page order and compaction target order + * and skip hugetlbfs pages. + */ + if (skip_isolation_on_order(order, cc->order) || + PageHuge(page)) { + if (order <= MAX_PAGE_ORDER) { + low_pfn += (1UL << order) - 1; + nr_scanned += (1UL << order) - 1; + } + goto isolate_fail; } - goto isolate_fail; } /* @@ -1146,10 +1168,11 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, } /* - * folio become large since the non-locked check, - * and it's on LRU. + * Check LRU folio order under the lock */ - if (unlikely(folio_test_large(folio) && !cc->alloc_contig)) { + if (unlikely(skip_isolation_on_order(folio_order(folio), + cc->order) && + !cc->alloc_contig)) { low_pfn += folio_nr_pages(folio) - 1; nr_scanned += folio_nr_pages(folio) - 1; folio_set_lru(folio); @@ -1767,6 +1790,10 @@ static struct folio *compaction_alloc(struct folio *src, unsigned long data) struct compact_control *cc = (struct compact_control *)data; struct folio *dst; + /* this makes migrate_pages() split the source page and retry */ + if (folio_test_large(src) > 0) + return NULL; + if (list_empty(&cc->freepages)) { isolate_freepages(cc); -- 2.43.0