[RFC PATCH 2/3] mm/mincore: use a helper for checking the swap cache

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

Introduce a mincore_swap helper for checking swap entries, seperate it
from page cache checking.

The new helper will only be called on swap address space, so it always
grab the swap device before checking the entry, caller won't need to
lock anything.

The sanity WARN_ON check will also cover all use case now, previously it
only worked for PTE checking.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/mincore.c | 58 ++++++++++++++++++++++++++++------------------------
 1 file changed, 31 insertions(+), 27 deletions(-)

diff --git a/mm/mincore.c b/mm/mincore.c
index f0d3c9419e58..1ac53acac239 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -47,6 +47,31 @@ static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
 	return 0;
 }
 
+static unsigned char mincore_swap(swp_entry_t entry)
+{
+	struct swap_info_struct *si;
+	struct folio *folio = NULL;
+	unsigned char present = 0;
+
+	if (!IS_ENABLED(CONFIG_SWAP)) {
+		WARN_ON(1);
+		return 1;
+	}
+
+	si = get_swap_device(entry);
+	if (si) {
+		folio = filemap_get_folio(swap_address_space(entry),
+					  swap_cache_index(entry));
+		put_swap_device(si);
+		if (folio) {
+			present = folio_test_uptodate(folio);
+			folio_put(folio);
+		}
+	}
+
+	return present;
+}
+
 /*
  * 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,
@@ -64,33 +89,18 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t index)
 	 * any other file mapping (ie. marked !present and faulted in with
 	 * tmpfs's .fault). So swapped out tmpfs mappings are tested here.
 	 */
-	if (IS_ENABLED(CONFIG_SWAP) && shmem_mapping(mapping)) {
-		folio = filemap_get_entry(mapping, index);
-		/*
-		 * shmem/tmpfs may return swap: account for swapcache
-		 * page too.
-		 */
+	folio = filemap_get_entry(mapping, index);
+	if (folio) {
 		if (xa_is_value(folio)) {
-			struct swap_info_struct *si;
 			swp_entry_t swp = radix_to_swp_entry(folio);
 			/* There might be swapin error entries in shmem mapping. */
 			if (non_swap_entry(swp))
 				return 0;
-			/* Prevent swap device to being swapoff under us */
-			si = get_swap_device(swp);
-			if (si) {
-				folio = filemap_get_folio(swap_address_space(swp),
-							  swap_cache_index(swp));
-				put_swap_device(si);
-			} else {
+			if (shmem_mapping(mapping))
+				return mincore_swap(swp);
+			else
 				return 0;
-			}
 		}
-	} else {
-		folio = filemap_get_folio(mapping, index);
-	}
-
-	if (folio) {
 		present = folio_test_uptodate(folio);
 		folio_put(folio);
 	}
@@ -177,13 +187,7 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 				 */
 				*vec = 1;
 			} else {
-#ifdef CONFIG_SWAP
-				*vec = mincore_page(swap_address_space(entry),
-						    swap_cache_index(entry));
-#else
-				WARN_ON(1);
-				*vec = 1;
-#endif
+				*vec = mincore_swap(entry);
 			}
 		}
 		vec += step;
-- 
2.50.1