[1/4] mm: Factor find_get_swap_page out of mincore_page

Commit Message

Matthew Wilcox July 10, 2020, 8:26 p.m. UTC

This function can also be used elsewhere.  I've left it in mincore.c for
now because I can't find a better place to put it.

Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
---
 include/linux/pagemap.h |  1 +
 mm/mincore.c            | 59 +++++++++++++++++++++++------------------
 2 files changed, 34 insertions(+), 26 deletions(-)

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index cf2468da68e9..b921581a7dcf 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -386,6 +386,7 @@  static inline struct page *find_subpage(struct page *head, pgoff_t index)
 
 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
 struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset);
+struct page *find_get_swap_page(struct address_space *mapping, pgoff_t index);
 unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
 			  unsigned int nr_entries, struct page **entries,
 			  pgoff_t *indices);
diff --git a/mm/mincore.c b/mm/mincore.c
index 453ff112470f..abc24ca6f0f7 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -42,13 +42,44 @@  static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
 	return 0;
 }
 
+/**
+ * find_get_swap_page - Find and get a page from the page or swap caches.
+ * @mapping: The address_space to search.
+ * @index: The page cache index.
+ *
+ * This is like find_get_page(), but if we find a swap entry for
+ * shmem/tmpfs, we also look in the swap cache for the page.
+ *
+ * Return: The found page or %NULL.
+ */
+struct page *find_get_swap_page(struct address_space *mapping, pgoff_t index)
+{
+	swp_entry_t swp;
+	struct swap_info_struct *si;
+	struct page *page = find_get_entry(mapping, index);
+
+	if (!xa_is_value(page))
+		return page;
+	if (!IS_ENABLED(CONFIG_SWAP) || !shmem_mapping(mapping))
+		return NULL;
+
+	swp = radix_to_swp_entry(page);
+	/* Prevent swapoff from happening to us */
+	si = get_swap_device(swp);
+	if (!si)
+		return NULL;
+	page = find_get_page(swap_address_space(swp), swp_offset(swp));
+	put_swap_device(si);
+	return page;
+}
+
 /*
  * Later we can get more picky about what "in core" means precisely.
  * For now, simply check to see if the page is in the page cache,
  * and is up to date; i.e. that no page-in operation would be required
  * at this time if an application were to map and access this page.
  */
-static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
+static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
 {
 	unsigned char present = 0;
 	struct page *page;
@@ -59,31 +90,7 @@  static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
 	 * any other file mapping (ie. marked !present and faulted in with
 	 * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
 	 */
-#ifdef CONFIG_SWAP
-	if (shmem_mapping(mapping)) {
-		page = find_get_entry(mapping, pgoff);
-		/*
-		 * shmem/tmpfs may return swap: account for swapcache
-		 * page too.
-		 */
-		if (xa_is_value(page)) {
-			swp_entry_t swp = radix_to_swp_entry(page);
-			struct swap_info_struct *si;
-
-			/* Prevent swap device to being swapoff under us */
-			si = get_swap_device(swp);
-			if (si) {
-				page = find_get_page(swap_address_space(swp),
-						     swp_offset(swp));
-				put_swap_device(si);
-			} else
-				page = NULL;
-		}
-	} else
-		page = find_get_page(mapping, pgoff);
-#else
-	page = find_get_page(mapping, pgoff);
-#endif
+	page = find_get_swap_page(mapping, index);
 	if (page) {
 		present = PageUptodate(page);
 		put_page(page);