mm: return the folio from swapin_readahead

The unuse_pte_range() caller only wants the folio while do_swap_page()
wants both the page and the folio.  Since do_swap_page() already has logic
for handling both the folio and the page, move the folio-to-page logic
there.  This also lets us allocate larger folios in the SWP_SYNCHRONOUS_IO
path in future.

Link: https://lkml.kernel.org/r/20240807193734.1865400-1-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -4091,7 +4091,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 			/* skip swapcache */
 			folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0,
 						vma, vmf->address, false);
-			page = &folio->page;
 			if (folio) {
 				__folio_set_locked(folio);
 				__folio_set_swapbacked(folio);
@@ -4116,10 +4115,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 				folio->private = NULL;
 			}
 		} else {
-			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
+			folio = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
 						vmf);
-			if (page)
-				folio = page_folio(page);
 			swapcache = folio;
 		}
 
@@ -4140,6 +4137,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		ret = VM_FAULT_MAJOR;
 		count_vm_event(PGMAJFAULT);
 		count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
+		page = folio_file_page(folio, swp_offset(entry));
 	} else if (PageHWPoison(page)) {
 		/*
 		 * hwpoisoned dirty swapcache pages are kept for killing

mm/swap.h

@@ -73,7 +73,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_flags,
 		bool skip_if_exists);
 struct folio *swap_cluster_readahead(swp_entry_t entry, gfp_t flag,
 		struct mempolicy *mpol, pgoff_t ilx);
-struct page *swapin_readahead(swp_entry_t entry, gfp_t flag,
+struct folio *swapin_readahead(swp_entry_t entry, gfp_t flag,
 		struct vm_fault *vmf);
 
 static inline unsigned int folio_swap_flags(struct folio *folio)
@@ -109,7 +109,7 @@ static inline struct folio *swap_cluster_readahead(swp_entry_t entry,
 	return NULL;
 }
 
-static inline struct page *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
+static inline struct folio *swapin_readahead(swp_entry_t swp, gfp_t gfp_mask,
 			struct vm_fault *vmf)
 {
 	return NULL;

mm/swap_state.c

@@ -863,13 +863,13 @@ static struct folio *swap_vma_readahead(swp_entry_t targ_entry, gfp_t gfp_mask,
  * @gfp_mask: memory allocation flags
  * @vmf: fault information
  *
- * Returns the struct page for entry and addr, after queueing swapin.
+ * Returns the struct folio for entry and addr, after queueing swapin.
  *
  * It's a main entry function for swap readahead. By the configuration,
  * it will read ahead blocks by cluster-based(ie, physical disk based)
  * or vma-based(ie, virtual address based on faulty address) readahead.
  */
-struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
+struct folio *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 				struct vm_fault *vmf)
 {
 	struct mempolicy *mpol;
@@ -882,9 +882,7 @@ struct page *swapin_readahead(swp_entry_t entry, gfp_t gfp_mask,
 		swap_cluster_readahead(entry, gfp_mask, mpol, ilx);
 	mpol_cond_put(mpol);
 
-	if (!folio)
-		return NULL;
-	return folio_file_page(folio, swp_offset(entry));
+	return folio;
 }
 
 #ifdef CONFIG_SYSFS

mm/swapfile.c

@@ -1980,7 +1980,6 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 
 		folio = swap_cache_get_folio(entry, vma, addr);
 		if (!folio) {
-			struct page *page;
 			struct vm_fault vmf = {
 				.vma = vma,
 				.address = addr,
@@ -1988,10 +1987,8 @@ static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 				.pmd = pmd,
 			};
 
-			page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
+			folio = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
 						&vmf);
-			if (page)
-				folio = page_folio(page);
 		}
 		if (!folio) {
 			swp_count = READ_ONCE(si->swap_map[offset]);