[PATCH v4 08/12] mm/swapfile: Add batched version of folio_put_swap

[Dev Jain <dev.jain@arm.com>]

Add folio_put_swap_pages to handle a batch of consecutive pages. Note
that folio_put_swap already can handle a subset of this: nr_pages == 1 and
nr_pages == folio_nr_pages(folio). Generalize this to any nr_pages.

Currently we have a not-so-nice logic of passing in subpage == NULL if
we mean to exercise the logic on the entire folio, and subpage != NULL if
we want to exercise the logic on only that subpage. Remove this
indirection: the caller invokes folio_put_swap_pages() if it wants to
operate on a range of pages in the folio (i.e nr_pages may be anything
between 1 till folio_nr_pages()), and invokes folio_put_swap() if it
wants to operate on the entire folio.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
 mm/memory.c   |  6 +++---
 mm/rmap.c     |  4 ++--
 mm/shmem.c    |  6 +++---
 mm/swap.h     | 17 +++++++++++++++--
 mm/swapfile.c | 17 ++++++++---------
 5 files changed, 31 insertions(+), 19 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 767c033e95da9..40cd44a7f10a1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5165,7 +5165,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	if (unlikely(folio != swapcache)) {
 		folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE);
 		folio_add_lru_vma(folio, vma);
-		folio_put_swap(swapcache, NULL);
+		folio_put_swap(swapcache);
 	} else if (!folio_test_anon(folio)) {
 		/*
 		 * We currently only expect !anon folios that are fully
@@ -5174,12 +5174,12 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		VM_WARN_ON_ONCE_FOLIO(folio_nr_pages(folio) != nr_pages, folio);
 		VM_WARN_ON_ONCE_FOLIO(folio_mapped(folio), folio);
 		folio_add_new_anon_rmap(folio, vma, address, rmap_flags);
-		folio_put_swap(folio, NULL);
+		folio_put_swap(folio);
 	} else {
 		VM_WARN_ON_ONCE(nr_pages != 1 && nr_pages != folio_nr_pages(folio));
 		folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address,
 					 rmap_flags);
-		folio_put_swap(folio, nr_pages == 1 ? page : NULL);
+		folio_put_swap_pages(folio, page, nr_pages);
 	}
 
 	VM_BUG_ON(!folio_test_anon(folio) ||
diff --git a/mm/rmap.c b/mm/rmap.c
index 3065d384cadf8..c0e385882f562 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2342,7 +2342,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			 * so we'll not check/care.
 			 */
 			if (arch_unmap_one(mm, vma, address, pteval) < 0) {
-				folio_put_swap(folio, subpage);
+				folio_put_swap_pages(folio, subpage, 1);
 				set_pte_at(mm, address, pvmw.pte, pteval);
 				goto walk_abort;
 			}
@@ -2350,7 +2350,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 			/* See folio_try_share_anon_rmap(): clear PTE first. */
 			if (anon_exclusive &&
 			    folio_try_share_anon_rmap_pte(folio, subpage)) {
-				folio_put_swap(folio, subpage);
+				folio_put_swap_pages(folio, subpage, 1);
 				set_pte_at(mm, address, pvmw.pte, pteval);
 				goto walk_abort;
 			}
diff --git a/mm/shmem.c b/mm/shmem.c
index 5e4f521399847..bb7e0fc305d87 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1719,7 +1719,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
 		/* Swap entry might be erased by racing shmem_free_swap() */
 		if (!error) {
 			shmem_recalc_inode(inode, 0, -nr_pages);
-			folio_put_swap(folio, NULL);
+			folio_put_swap(folio);
 		}
 
 		/*
@@ -2199,7 +2199,7 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,
 
 	nr_pages = folio_nr_pages(folio);
 	folio_wait_writeback(folio);
-	folio_put_swap(folio, NULL);
+	folio_put_swap(folio);
 	swap_cache_del_folio(folio);
 	/*
 	 * Don't treat swapin error folio as alloced. Otherwise inode->i_blocks
@@ -2429,7 +2429,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 	if (sgp == SGP_WRITE)
 		folio_mark_accessed(folio);
 
-	folio_put_swap(folio, NULL);
+	folio_put_swap(folio);
 	swap_cache_del_folio(folio);
 	folio_mark_dirty(folio);
 	put_swap_device(si);
diff --git a/mm/swap.h b/mm/swap.h
index 36c69b2788c77..48e8deb95a440 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -208,7 +208,8 @@ extern int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp);
 int folio_alloc_swap(struct folio *folio);
 int folio_dup_swap_pages(struct folio *folio, struct page *page,
 			 unsigned long nr_pages);
-void folio_put_swap(struct folio *folio, struct page *page);
+void folio_put_swap_pages(struct folio *folio, struct page *page,
+			  unsigned long nr_pages);
 
 /* For internal use */
 extern void __swap_cluster_free_entries(struct swap_info_struct *si,
@@ -397,7 +398,8 @@ static inline int folio_dup_swap_pages(struct folio *folio, struct page *page,
 	return -EINVAL;
 }
 
-static inline void folio_put_swap(struct folio *folio, struct page *page)
+static inline void folio_put_swap_pages(struct folio *folio, struct page *page,
+				  unsigned long nr_pages)
 {
 }
 
@@ -514,4 +516,15 @@ static inline int folio_dup_swap(struct folio *folio)
 				    folio_nr_pages(folio));
 }
 
+/**
+ * folio_put_swap() - Decrease swap count of all swap entries of a folio.
+ * @folio: folio with swap entries bound.
+ *
+ * See folio_put_swap_pages() for more information.
+ */
+static inline void folio_put_swap(struct folio *folio)
+{
+	folio_put_swap_pages(folio, folio_page(folio, 0), folio_nr_pages(folio));
+}
+
 #endif /* _MM_SWAP_H */
diff --git a/mm/swapfile.c b/mm/swapfile.c
index c91957149ecce..f1d97989cee31 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1773,27 +1773,25 @@ int folio_dup_swap_pages(struct folio *folio, struct page *page,
 }
 
 /**
- * folio_put_swap() - Decrease swap count of swap entries of a folio.
+ * folio_put_swap_pages() - Decrease swap count of swap entries of a folio.
  * @folio: folio with swap entries bounded, must be in swap cache and locked.
- * @page: if not NULL, only decrease the swap count of this page.
+ * @page: the first page in the folio to decrease the swap count for.
+ * @nr_pages: the number of pages in the folio to decrease the swap count for.
  *
  * This won't free the swap slots even if swap count drops to zero, they are
  * still pinned by the swap cache. User may call folio_free_swap to free them.
  * Context: Caller must ensure the folio is locked and in the swap cache.
  */
-void folio_put_swap(struct folio *folio, struct page *page)
+void folio_put_swap_pages(struct folio *folio, struct page *page,
+			  unsigned long nr_pages)
 {
 	swp_entry_t entry = folio->swap;
-	unsigned long nr_pages = folio_nr_pages(folio);
 	struct swap_info_struct *si = __swap_entry_to_info(entry);
 
 	VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
 	VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio);
 
-	if (page) {
-		entry.val += folio_page_idx(folio, page);
-		nr_pages = 1;
-	}
+	entry.val += folio_page_idx(folio, page);
 
 	swap_put_entries_cluster(si, swp_offset(entry), nr_pages, false);
 }
@@ -2499,7 +2497,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		new_pte = pte_mkuffd_wp(new_pte);
 setpte:
 	set_pte_at(vma->vm_mm, addr, pte, new_pte);
-	folio_put_swap(swapcache, folio_file_page(swapcache, swp_offset(entry)));
+	folio_put_swap_pages(swapcache,
+			     folio_file_page(swapcache, swp_offset(entry)), 1);
 out:
 	if (pte)
 		pte_unmap_unlock(pte, ptl);
-- 
2.34.1