Userfaultfd checks whether a swap entry is in swapcache. This is currently done by directly looking at the swapfile's swap map - however, the swap cached state will soon be managed at the virtual swap layer. Abstract away this function. Signed-off-by: Nhat Pham --- include/linux/swap.h | 6 ++++++ mm/swapfile.c | 15 +++++++++++++++ mm/userfaultfd.c | 3 +-- 3 files changed, 22 insertions(+), 2 deletions(-) diff --git a/include/linux/swap.h b/include/linux/swap.h index 3da637b218baf..f91a442ac0e82 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -435,6 +435,7 @@ void free_swap_and_cache_nr(swp_entry_t entry, int nr); int __swap_count(swp_entry_t entry); bool swap_entry_swapped(struct swap_info_struct *si, swp_entry_t entry); int swp_swapcount(swp_entry_t entry); +bool is_swap_cached(swp_entry_t entry); /* Swap cache API (mm/swap_state.c) */ static inline unsigned long total_swapcache_pages(void) @@ -554,6 +555,11 @@ static inline int swp_swapcount(swp_entry_t entry) return 0; } +static inline bool is_swap_cached(swp_entry_t entry) +{ + return false; +} + static inline int folio_alloc_swap(struct folio *folio) { return -EINVAL; diff --git a/mm/swapfile.c b/mm/swapfile.c index cacfafa9a540d..3c89dedbd5718 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -194,6 +194,21 @@ static bool swap_only_has_cache(struct swap_info_struct *si, return true; } +/** + * is_swap_cached - check if the swap entry is cached + * @entry: swap entry to check + * + * Check swap_map directly to minimize overhead, READ_ONCE is sufficient. + * + * Returns true if the swap entry is cached, false otherwise. + */ +bool is_swap_cached(swp_entry_t entry) +{ + struct swap_info_struct *si = __swap_entry_to_info(entry); + + return READ_ONCE(si->swap_map[swp_offset(entry)]) & SWAP_HAS_CACHE; +} + static bool swap_is_last_map(struct swap_info_struct *si, unsigned long offset, int nr_pages, bool *has_cache) { diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 25f89eba0438c..98be764fb3ecd 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -1190,7 +1190,6 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, * Check if the swap entry is cached after acquiring the src_pte * lock. Otherwise, we might miss a newly loaded swap cache folio. * - * Check swap_map directly to minimize overhead, READ_ONCE is sufficient. * We are trying to catch newly added swap cache, the only possible case is * when a folio is swapped in and out again staying in swap cache, using the * same entry before the PTE check above. The PTL is acquired and released @@ -1200,7 +1199,7 @@ static int move_swap_pte(struct mm_struct *mm, struct vm_area_struct *dst_vma, * cache, or during the tiny synchronization window between swap cache and * swap_map, but it will be gone very quickly, worst result is retry jitters. */ - if (READ_ONCE(si->swap_map[swp_offset(entry)]) & SWAP_HAS_CACHE) { + if (is_swap_cached(entry)) { double_pt_unlock(dst_ptl, src_ptl); return -EAGAIN; } -- 2.47.3