ext4: convert mext_page_double_lock() to mext_folio_double_lock()

Convert mext_page_double_lock() to use folios.  This change saves 146
bytes of kernel text.  It also removes 6 calls to compound_head() and 2
calls to folio_file_page().

Link: https://lkml.kernel.org/r/20221207181009.4016-1-vishal.moola@gmail.comSigned-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/ext4/move_extent.c

@@ -110,22 +110,23 @@ mext_check_coverage(struct inode *inode, ext4_lblk_t from, ext4_lblk_t count,
 }
 
 /**
- * mext_page_double_lock - Grab and lock pages on both @inode1 and @inode2
+ * mext_folio_double_lock - Grab and lock folio on both @inode1 and @inode2
  *
  * @inode1:	the inode structure
  * @inode2:	the inode structure
- * @index1:	page index
- * @index2:	page index
- * @page:	result page vector
+ * @index1:	folio index
+ * @index2:	folio index
+ * @folio:	result folio vector
  *
- * Grab two locked pages for inode's by inode order
+ * Grab two locked folio for inode's by inode order
  */
 static int
-mext_page_double_lock(struct inode *inode1, struct inode *inode2,
-		      pgoff_t index1, pgoff_t index2, struct page *page[2])
+mext_folio_double_lock(struct inode *inode1, struct inode *inode2,
+		      pgoff_t index1, pgoff_t index2, struct folio *folio[2])
 {
 	struct address_space *mapping[2];
 	unsigned int flags;
+	unsigned fgp_flags = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE;
 
 	BUG_ON(!inode1 || !inode2);
 	if (inode1 < inode2) {
@@ -138,28 +139,30 @@ mext_page_double_lock(struct inode *inode1, struct inode *inode2,
 	}
 
 	flags = memalloc_nofs_save();
-	page[0] = grab_cache_page_write_begin(mapping[0], index1);
-	if (!page[0]) {
+	folio[0] = __filemap_get_folio(mapping[0], index1, fgp_flags,
+			mapping_gfp_mask(mapping[0]));
+	if (!folio[0]) {
 		memalloc_nofs_restore(flags);
 		return -ENOMEM;
 	}
 
-	page[1] = grab_cache_page_write_begin(mapping[1], index2);
+	folio[1] = __filemap_get_folio(mapping[1], index2, fgp_flags,
+			mapping_gfp_mask(mapping[1]));
 	memalloc_nofs_restore(flags);
-	if (!page[1]) {
-		unlock_page(page[0]);
-		put_page(page[0]);
+	if (!folio[1]) {
+		folio_unlock(folio[0]);
+		folio_put(folio[0]);
 		return -ENOMEM;
 	}
 	/*
-	 * grab_cache_page_write_begin() may not wait on page's writeback if
+	 * __filemap_get_folio() may not wait on folio's writeback if
 	 * BDI not demand that. But it is reasonable to be very conservative
-	 * here and explicitly wait on page's writeback
+	 * here and explicitly wait on folio's writeback
 	 */
-	wait_on_page_writeback(page[0]);
-	wait_on_page_writeback(page[1]);
+	folio_wait_writeback(folio[0]);
+	folio_wait_writeback(folio[1]);
 	if (inode1 > inode2)
-		swap(page[0], page[1]);
+		swap(folio[0], folio[1]);
 
 	return 0;
 }
@@ -252,7 +255,6 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 		     int block_len_in_page, int unwritten, int *err)
 {
 	struct inode *orig_inode = file_inode(o_filp);
-	struct page *pagep[2] = {NULL, NULL};
 	struct folio *folio[2] = {NULL, NULL};
 	handle_t *handle;
 	ext4_lblk_t orig_blk_offset, donor_blk_offset;
@@ -303,8 +305,8 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 
 	replaced_size = data_size;
 
-	*err = mext_page_double_lock(orig_inode, donor_inode, orig_page_offset,
-				     donor_page_offset, pagep);
+	*err = mext_folio_double_lock(orig_inode, donor_inode, orig_page_offset,
+				     donor_page_offset, folio);
 	if (unlikely(*err < 0))
 		goto stop_journal;
 	/*
@@ -314,8 +316,6 @@ move_extent_per_page(struct file *o_filp, struct inode *donor_inode,
 	 * hold page's lock, if it is still the case data copy is not
 	 * necessary, just swap data blocks between orig and donor.
 	 */
-	folio[0] = page_folio(pagep[0]);
-	folio[1] = page_folio(pagep[1]);
 
 	VM_BUG_ON_FOLIO(folio_test_large(folio[0]), folio[0]);
 	VM_BUG_ON_FOLIO(folio_test_large(folio[1]), folio[1]);