[PATCH 1/3] filemap: Convert filemap_map_pmd() to take a folio

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Save a few calls to compound_head().  We specify exactly which page from
the folio to use by passing in start_pgoff, which means this will work
for a folio which is larger than PMD size.  The rest of the VM isn't
prepared for that yet, but now this function is.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 mm/filemap.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 31bf18ec6d01..b6b7efc9abc0 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3259,22 +3259,24 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
 }
 EXPORT_SYMBOL(filemap_fault);
 
-static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
+static bool filemap_map_pmd(struct vm_fault *vmf, struct folio *folio,
+		pgoff_t start)
 {
 	struct mm_struct *mm = vmf->vma->vm_mm;
 
 	/* Huge page is mapped? No need to proceed. */
 	if (pmd_trans_huge(*vmf->pmd)) {
-		unlock_page(page);
-		put_page(page);
+		folio_unlock(folio);
+		folio_put(folio);
 		return true;
 	}
 
-	if (pmd_none(*vmf->pmd) && PageTransHuge(page)) {
+	if (pmd_none(*vmf->pmd) && folio_test_pmd_mappable(folio)) {
+		struct page *page = folio_file_page(folio, start);
 		vm_fault_t ret = do_set_pmd(vmf, page);
 		if (!ret) {
 			/* The page is mapped successfully, reference consumed. */
-			unlock_page(page);
+			folio_unlock(folio);
 			return true;
 		}
 	}
@@ -3284,8 +3286,8 @@ static bool filemap_map_pmd(struct vm_fault *vmf, struct page *page)
 
 	/* See comment in handle_pte_fault() */
 	if (pmd_devmap_trans_unstable(vmf->pmd)) {
-		unlock_page(page);
-		put_page(page);
+		folio_unlock(folio);
+		folio_put(folio);
 		return true;
 	}
 
@@ -3368,7 +3370,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
 	if (!folio)
 		goto out;
 
-	if (filemap_map_pmd(vmf, &folio->page)) {
+	if (filemap_map_pmd(vmf, folio, start_pgoff)) {
 		ret = VM_FAULT_NOPAGE;
 		goto out;
 	}
-- 
2.35.1