diff options
| -rw-r--r-- | include/linux/swap.h | 3 | ||||
| -rw-r--r-- | mm/huge_memory.c | 12 | ||||
| -rw-r--r-- | mm/swapfile.c | 3 |
3 files changed, 16 insertions, 2 deletions
diff --git a/include/linux/swap.h b/include/linux/swap.h index 066bd21765ad..a282933c5bc6 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -538,7 +538,8 @@ static inline int swp_swapcount(swp_entry_t entry) return 0; } -#define reuse_swap_page(page) (page_mapcount(page) == 1) +#define reuse_swap_page(page) \ + (!PageTransCompound(page) && page_mapcount(page) == 1) static inline int try_to_free_swap(struct page *page) { diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 4211682f223b..e45918d058b9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1199,7 +1199,17 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, page = pmd_page(orig_pmd); VM_BUG_ON_PAGE(!PageCompound(page) || !PageHead(page), page); - if (page_mapcount(page) == 1) { + /* + * We can only reuse the page if nobody else maps the huge page or it's + * part. We can do it by checking page_mapcount() on each sub-page, but + * it's expensive. + * The cheaper way is to check page_count() to be equal 1: every + * mapcount takes page reference reference, so this way we can + * guarantee, that the PMD is the only mapping. + * This can give false negative if somebody pinned the page, but that's + * fine. + */ + if (page_mapcount(page) == 1 && page_count(page) == 1) { pmd_t entry; entry = pmd_mkyoung(orig_pmd); entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); diff --git a/mm/swapfile.c b/mm/swapfile.c index efe26bb10adb..31dc94fb0f60 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -926,6 +926,9 @@ int reuse_swap_page(struct page *page) VM_BUG_ON_PAGE(!PageLocked(page), page); if (unlikely(PageKsm(page))) return 0; + /* The page is part of THP and cannot be reused */ + if (PageTransCompound(page)) + return 0; count = page_mapcount(page); if (count <= 1 && PageSwapCache(page)) { count += page_swapcount(page); |