[RFC PATCH 1/3] mm/mincore, swap: consolidate swap cache checking for mincore

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

The filemap_get_incore_folio (previously find_get_incore_page) helper
was introduced by commit 61ef18655704 ("mm: factor find_get_incore_page
out of mincore_page") to be used by later commit f5df8635c5a3 ("mm: use
find_get_incore_page in memcontrol"), so memory cgroup charge move code
can be simplified.

But commit 6b611388b626 ("memcg-v1: remove charge move code") removed
that user completely, it's only used by mincore now.

So this commit basically reverts commit 61ef18655704 ("mm: factor
find_get_incore_page out of mincore_page"). Move it back to mincore side
to simplify the code.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/mincore.c    | 29 +++++++++++++++++++++++++++--
 mm/swap.h       | 10 ----------
 mm/swap_state.c | 38 --------------------------------------
 3 files changed, 27 insertions(+), 50 deletions(-)

diff --git a/mm/mincore.c b/mm/mincore.c
index 10dabefc3acc..f0d3c9419e58 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -64,8 +64,33 @@ 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.
 	 */
-	folio = filemap_get_incore_folio(mapping, index);
-	if (!IS_ERR(folio)) {
+	if (IS_ENABLED(CONFIG_SWAP) && shmem_mapping(mapping)) {
+		folio = filemap_get_entry(mapping, index);
+		/*
+		 * shmem/tmpfs may return swap: account for swapcache
+		 * page too.
+		 */
+		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 {
+				return 0;
+			}
+		}
+	} else {
+		folio = filemap_get_folio(mapping, index);
+	}
+
+	if (folio) {
 		present = folio_test_uptodate(folio);
 		folio_put(folio);
 	}
diff --git a/mm/swap.h b/mm/swap.h
index 911ad5ff0f89..1ae44d4193b1 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -64,9 +64,6 @@ void clear_shadow_from_swap_cache(int type, unsigned long begin,
 void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr);
 struct folio *swap_cache_get_folio(swp_entry_t entry,
 		struct vm_area_struct *vma, unsigned long addr);
-struct folio *filemap_get_incore_folio(struct address_space *mapping,
-		pgoff_t index);
-
 struct folio *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		struct vm_area_struct *vma, unsigned long addr,
 		struct swap_iocb **plug);
@@ -178,13 +175,6 @@ static inline struct folio *swap_cache_get_folio(swp_entry_t entry,
 	return NULL;
 }
 
-static inline
-struct folio *filemap_get_incore_folio(struct address_space *mapping,
-		pgoff_t index)
-{
-	return filemap_get_folio(mapping, index);
-}
-
 static inline void *get_shadow_from_swap_cache(swp_entry_t entry)
 {
 	return NULL;
diff --git a/mm/swap_state.c b/mm/swap_state.c
index c354435a0923..99513b74b5d8 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -323,44 +323,6 @@ struct folio *swap_cache_get_folio(swp_entry_t entry,
 	return folio;
 }
 
-/**
- * filemap_get_incore_folio - Find and get a folio from the page or swap caches.
- * @mapping: The address_space to search.
- * @index: The page cache index.
- *
- * This differs from filemap_get_folio() in that it will also look for the
- * folio in the swap cache.
- *
- * Return: The found folio or %NULL.
- */
-struct folio *filemap_get_incore_folio(struct address_space *mapping,
-		pgoff_t index)
-{
-	swp_entry_t swp;
-	struct swap_info_struct *si;
-	struct folio *folio = filemap_get_entry(mapping, index);
-
-	if (!folio)
-		return ERR_PTR(-ENOENT);
-	if (!xa_is_value(folio))
-		return folio;
-	if (!shmem_mapping(mapping))
-		return ERR_PTR(-ENOENT);
-
-	swp = radix_to_swp_entry(folio);
-	/* There might be swapin error entries in shmem mapping. */
-	if (non_swap_entry(swp))
-		return ERR_PTR(-ENOENT);
-	/* Prevent swapoff from happening to us */
-	si = get_swap_device(swp);
-	if (!si)
-		return ERR_PTR(-ENOENT);
-	index = swap_cache_index(swp);
-	folio = filemap_get_folio(swap_address_space(swp), index);
-	put_swap_device(si);
-	return folio;
-}
-
 struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
 		struct mempolicy *mpol, pgoff_t ilx, bool *new_page_allocated,
 		bool skip_if_exists)
-- 
2.50.1