[PATCH 14/24] mm/swap: do shadow lookup as well when doing swap cache lookup

[Kairui Song]

From: Kairui Song <kasong@xxxxxxxxxxx>

Make swap_cache_get_folio capable of returning the shadow value when the
xarray contains a shadow instead of a valid folio. Just extend the
arguments to be used later.

Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
---
 mm/shmem.c      |  2 +-
 mm/swap.h       |  2 +-
 mm/swap_state.c | 11 +++++++----
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 72239061c655..f9ce4067c742 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1875,7 +1875,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 	}
 
 	/* Look it up and read it in.. */
-	folio = swap_cache_get_folio(swap, NULL);
+	folio = swap_cache_get_folio(swap, NULL, NULL);
 	if (!folio) {
 		/* Or update major stats only when swapin succeeds?? */
 		if (fault_type) {
diff --git a/mm/swap.h b/mm/swap.h
index e43e965f123f..da9deb5ba37d 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -47,7 +47,7 @@ void delete_from_swap_cache(struct folio *folio);
 void clear_shadow_from_swap_cache(int type, unsigned long begin,
 				  unsigned long end);
 struct folio *swap_cache_get_folio(swp_entry_t entry,
-				   struct vm_fault *vmf);
+				   struct vm_fault *vmf, void **shadowp);
 struct folio *filemap_get_incore_folio(struct address_space *mapping,
 		pgoff_t index);
 
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 3b5a34f47192..e057c79fb06f 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -334,14 +334,17 @@ static inline bool swap_use_vma_readahead(struct swap_info_struct *si)
  *
  * Caller must lock the swap device or hold a reference to keep it valid.
  */
-struct folio *swap_cache_get_folio(swp_entry_t entry, struct vm_fault *vmf)
+struct folio *swap_cache_get_folio(swp_entry_t entry, struct vm_fault *vmf, void **shadowp)
 {
 	bool vma_ra, readahead;
 	struct folio *folio;
 
-	folio = filemap_get_folio(swap_address_space(entry), swp_offset(entry));
-	if (IS_ERR(folio))
+	folio = filemap_get_entry(swap_address_space(entry), swp_offset(entry));
+	if (xa_is_value(folio)) {
+		if (shadowp)
+			*shadowp = folio;
 		return NULL;
+	}
 
 	/*
 	 * At the moment, we don't support PG_readahead for anon THP
@@ -923,7 +926,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 	struct page *page;
 	pgoff_t ilx;
 
-	folio = swap_cache_get_folio(entry, vmf);
+	folio = swap_cache_get_folio(entry, vmf, NULL);
 	if (folio) {
 		page = folio_file_page(folio, swp_offset(entry));
 		cache_result = SWAP_CACHE_HIT;
-- 
2.42.0