[RFC PATCH 1/2] swapfile: add a batched variant for swap_duplicate()

[Nhat Pham <nphamcs@xxxxxxxxx>]

Add swap_duplicate_nr(), the batched variant of swap_duplicate(), that
operates on multiple contiguous swap entries.

This will be used in the following patch to remove SWAP_MAP_SHMEM.

Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
---
 include/linux/swap.h | 10 ++++++++--
 mm/swapfile.c        | 13 +++++++++----
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index ca533b478c21..e6ab234be7be 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -483,7 +483,7 @@ extern swp_entry_t get_swap_page_of_type(int);
 extern int get_swap_pages(int n, swp_entry_t swp_entries[], int order);
 extern int add_swap_count_continuation(swp_entry_t, gfp_t);
 extern void swap_shmem_alloc(swp_entry_t, int);
-extern int swap_duplicate(swp_entry_t);
+extern int swap_duplicate_nr(swp_entry_t, int);
 extern int swapcache_prepare(swp_entry_t entry, int nr);
 extern void swap_free_nr(swp_entry_t entry, int nr_pages);
 extern void swapcache_free_entries(swp_entry_t *entries, int n);
@@ -553,7 +553,7 @@ static inline void swap_shmem_alloc(swp_entry_t swp, int nr)
 {
 }
 
-static inline int swap_duplicate(swp_entry_t swp)
+static inline int swap_duplicate_nr(swp_entry_t swp, int nr)
 {
 	return 0;
 }
@@ -606,6 +606,12 @@ static inline int add_swap_extent(struct swap_info_struct *sis,
 }
 #endif /* CONFIG_SWAP */
 
+static inline int swap_duplicate(swp_entry_t entry)
+{
+	return swap_duplicate_nr(entry, 1);
+}
+
+
 static inline void free_swap_and_cache(swp_entry_t entry)
 {
 	free_swap_and_cache_nr(entry, 1);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 0cded32414a1..47a2cd5f590d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3695,18 +3695,23 @@ void swap_shmem_alloc(swp_entry_t entry, int nr)
 	__swap_duplicate(entry, SWAP_MAP_SHMEM, nr);
 }
 
-/*
- * Increase reference count of swap entry by 1.
+/**
+ * swap_duplicate_nr() - Increase reference count of nr contiguous swap entries
+ *                       by 1.
+ *
+ * @entry: first swap entry from which we want to increase the refcount.
+ * @nr: Number of entries in range.
+ *
  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
  * might occur if a page table entry has got corrupted.
  */
-int swap_duplicate(swp_entry_t entry)
+int swap_duplicate_nr(swp_entry_t entry, int nr)
 {
 	int err = 0;
 
-	while (!err && __swap_duplicate(entry, 1, 1) == -ENOMEM)
+	while (!err && __swap_duplicate(entry, 1, nr) == -ENOMEM)
 		err = add_swap_count_continuation(entry, GFP_ATOMIC);
 	return err;
 }
-- 
2.43.5