ext4: convert mpage_prepare_extent_to_map() to use filemap_get_folios_tag()

Convert the function to use folios throughout.  This is in preparation for
the removal of find_get_pages_range_tag().  Now supports large folios. 
This change removes 11 calls to compound_head().

Link: https://lkml.kernel.org/r/20230104211448.4804-11-vishal.moola@gmail.comSigned-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/ext4/inode.c

@@ -2595,8 +2595,8 @@ static bool ext4_page_nomap_can_writeout(struct page *page)
 static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 {
 	struct address_space *mapping = mpd->inode->i_mapping;
-	struct pagevec pvec;
-	unsigned int nr_pages;
+	struct folio_batch fbatch;
+	unsigned int nr_folios;
 	long left = mpd->wbc->nr_to_write;
 	pgoff_t index = mpd->first_page;
 	pgoff_t end = mpd->last_page;
@@ -2610,18 +2610,17 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 		tag = PAGECACHE_TAG_TOWRITE;
 	else
 		tag = PAGECACHE_TAG_DIRTY;
-
-	pagevec_init(&pvec);
+	folio_batch_init(&fbatch);
 	mpd->map.m_len = 0;
 	mpd->next_page = index;
 	while (index <= end) {
-		nr_pages = pagevec_lookup_range_tag(&pvec, mapping, &index, end,
-				tag);
-		if (nr_pages == 0)
+		nr_folios = filemap_get_folios_tag(mapping, &index, end,
+				tag, &fbatch);
+		if (nr_folios == 0)
 			break;
 
-		for (i = 0; i < nr_pages; i++) {
-			struct page *page = pvec.pages[i];
+		for (i = 0; i < nr_folios; i++) {
+			struct folio *folio = fbatch.folios[i];
 
 			/*
 			 * Accumulated enough dirty pages? This doesn't apply
@@ -2635,10 +2634,10 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 				goto out;
 
 			/* If we can't merge this page, we are done. */
-			if (mpd->map.m_len > 0 && mpd->next_page != page->index)
+			if (mpd->map.m_len > 0 && mpd->next_page != folio->index)
 				goto out;
 
-			lock_page(page);
+			folio_lock(folio);
 			/*
 			 * If the page is no longer dirty, or its mapping no
 			 * longer corresponds to inode we are writing (which
@@ -2646,16 +2645,16 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 			 * page is already under writeback and we are not doing
 			 * a data integrity writeback, skip the page
 			 */
-			if (!PageDirty(page) ||
-			    (PageWriteback(page) &&
+			if (!folio_test_dirty(folio) ||
+			    (folio_test_writeback(folio) &&
 			     (mpd->wbc->sync_mode == WB_SYNC_NONE)) ||
-			    unlikely(page->mapping != mapping)) {
-				unlock_page(page);
+			    unlikely(folio->mapping != mapping)) {
+				folio_unlock(folio);
 				continue;
 			}
 
-			wait_on_page_writeback(page);
-			BUG_ON(PageWriteback(page));
+			folio_wait_writeback(folio);
+			BUG_ON(folio_test_writeback(folio));
 
 			/*
 			 * Should never happen but for buggy code in
@@ -2666,49 +2665,49 @@ static int mpage_prepare_extent_to_map(struct mpage_da_data *mpd)
 			 *
 			 * [1] https://lore.kernel.org/linux-mm/20180103100430.GE4911@quack2.suse.cz
 			 */
-			if (!page_has_buffers(page)) {
-				ext4_warning_inode(mpd->inode, "page %lu does not have buffers attached", page->index);
-				ClearPageDirty(page);
-				unlock_page(page);
+			if (!folio_buffers(folio)) {
+				ext4_warning_inode(mpd->inode, "page %lu does not have buffers attached", folio->index);
+				folio_clear_dirty(folio);
+				folio_unlock(folio);
 				continue;
 			}
 
 			if (mpd->map.m_len == 0)
-				mpd->first_page = page->index;
-			mpd->next_page = page->index + 1;
+				mpd->first_page = folio->index;
+			mpd->next_page = folio->index + folio_nr_pages(folio);
 			/*
 			 * Writeout for transaction commit where we cannot
 			 * modify metadata is simple. Just submit the page.
 			 */
 			if (!mpd->can_map) {
-				if (ext4_page_nomap_can_writeout(page)) {
-					err = mpage_submit_page(mpd, page);
+				if (ext4_page_nomap_can_writeout(&folio->page)) {
+					err = mpage_submit_page(mpd, &folio->page);
 					if (err < 0)
 						goto out;
 				} else {
-					unlock_page(page);
-					mpd->first_page++;
+					folio_unlock(folio);
+					mpd->first_page += folio_nr_pages(folio);
 				}
 			} else {
 				/* Add all dirty buffers to mpd */
-				lblk = ((ext4_lblk_t)page->index) <<
+				lblk = ((ext4_lblk_t)folio->index) <<
 					(PAGE_SHIFT - blkbits);
-				head = page_buffers(page);
+				head = folio_buffers(folio);
 				err = mpage_process_page_bufs(mpd, head, head,
-							      lblk);
+						lblk);
 				if (err <= 0)
 					goto out;
 				err = 0;
 			}
-			left--;
+			left -= folio_nr_pages(folio);
 		}
-		pagevec_release(&pvec);
+		folio_batch_release(&fbatch);
 		cond_resched();
 	}
 	mpd->scanned_until_end = 1;
 	return 0;
 out:
-	pagevec_release(&pvec);
+	folio_batch_release(&fbatch);
 	return err;
 }