From d532e2e57e3c53ce74e519a07d7d2244482b7bd8 Mon Sep 17 00:00:00 2001 From: Yang Shi Date: Mon, 14 Dec 2020 19:13:16 -0800 Subject: mm: migrate: return -ENOSYS if THP migration is unsupported In the current implementation unmap_and_move() would return -ENOMEM if THP migration is unsupported, then the THP will be split. If split is failed just exit without trying to migrate other pages. It doesn't make too much sense since there may be enough free memory to migrate other pages and there may be a lot base pages on the list. Return -ENOSYS to make consistent with hugetlb. And if THP split is failed just skip and try other pages on the list. Just skip the whole list and exit when free memory is really low. Link: https://lkml.kernel.org/r/20201113205359.556831-6-shy828301@gmail.com Signed-off-by: Yang Shi Cc: Jan Kara Cc: Matthew Wilcox Cc: Mel Gorman Cc: Michal Hocko Cc: Song Liu Cc: Zi Yan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/migrate.c | 62 ++++++++++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 46 insertions(+), 16 deletions(-) (limited to 'mm/migrate.c') diff --git a/mm/migrate.c b/mm/migrate.c index 76e2a6f3749f..4749e52106ba 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1171,7 +1171,7 @@ static int unmap_and_move(new_page_t get_new_page, struct page *newpage = NULL; if (!thp_migration_supported() && PageTransHuge(page)) - return -ENOMEM; + return -ENOSYS; if (page_count(page) == 1) { /* page was freed from under us. So we are done. */ @@ -1378,6 +1378,20 @@ out: return rc; } +static inline int try_split_thp(struct page *page, struct page **page2, + struct list_head *from) +{ + int rc = 0; + + lock_page(page); + rc = split_huge_page_to_list(page, from); + unlock_page(page); + if (!rc) + list_safe_reset_next(page, *page2, lru); + + return rc; +} + /* * migrate_pages - migrate the pages specified in a list, to the free pages * supplied as the target for the page migration @@ -1455,24 +1469,40 @@ retry: * from list */ switch(rc) { + /* + * THP migration might be unsupported or the + * allocation could've failed so we should + * retry on the same page with the THP split + * to base pages. + * + * Head page is retried immediately and tail + * pages are added to the tail of the list so + * we encounter them after the rest of the list + * is processed. + */ + case -ENOSYS: + /* THP migration is unsupported */ + if (is_thp) { + if (!try_split_thp(page, &page2, from)) { + nr_thp_split++; + goto retry; + } + + nr_thp_failed++; + nr_failed += nr_subpages; + break; + } + + /* Hugetlb migration is unsupported */ + nr_failed++; + break; case -ENOMEM: /* - * THP migration might be unsupported or the - * allocation could've failed so we should - * retry on the same page with the THP split - * to base pages. - * - * Head page is retried immediately and tail - * pages are added to the tail of the list so - * we encounter them after the rest of the list - * is processed. + * When memory is low, don't bother to try to migrate + * other pages, just exit. */ if (is_thp) { - lock_page(page); - rc = split_huge_page_to_list(page, from); - unlock_page(page); - if (!rc) { - list_safe_reset_next(page, page2, lru); + if (!try_split_thp(page, &page2, from)) { nr_thp_split++; goto retry; } @@ -1500,7 +1530,7 @@ retry: break; default: /* - * Permanent failure (-EBUSY, -ENOSYS, etc.): + * Permanent failure (-EBUSY, etc.): * unlike -EAGAIN case, the failed page is * removed from migration page list and not * retried in the next outer loop. -- cgit v1.2.3-70-g09d2