f2fs: convert f2fs_sync_meta_pages() to use filemap_get_folios_tag()

Convert function to use folios throughout.  This is in preparation for the
removal of find_get_pages_range_tag().  This change removes 5 calls to
compound_head().

Initially the function was checking if the previous page index is truly
the previous page i.e.  1 index behind the current page.  To convert to
folios and maintain this check we need to make the check folio->index !=
prev + folio_nr_pages(previous folio) since we don't know how many pages
are in a folio.

At index i == 0 the check is guaranteed to succeed, so to workaround
indexing bounds we can simply ignore the check for that specific index. 
This makes the initial assignment of prev trivial, so I removed that as
well.

Also modify a comment in commit_checkpoint for consistency.

Link: https://lkml.kernel.org/r/20230104211448.4804-17-vishal.moola@gmail.comSigned-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Acked-by: Chao Yu <chao@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/f2fs/checkpoint.c

@@ -395,59 +395,62 @@ long f2fs_sync_meta_pages(struct f2fs_sb_info *sbi, enum page_type type,
 {
 	struct address_space *mapping = META_MAPPING(sbi);
 	pgoff_t index = 0, prev = ULONG_MAX;
-	struct pagevec pvec;
+	struct folio_batch fbatch;
 	long nwritten = 0;
-	int nr_pages;
+	int nr_folios;
 	struct writeback_control wbc = {
 		.for_reclaim = 0,
 	};
 	struct blk_plug plug;
 
-	pagevec_init(&pvec);
+	folio_batch_init(&fbatch);
 
 	blk_start_plug(&plug);
 
-	while ((nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
-				PAGECACHE_TAG_DIRTY))) {
+	while ((nr_folios = filemap_get_folios_tag(mapping, &index,
+					(pgoff_t)-1,
+					PAGECACHE_TAG_DIRTY, &fbatch))) {
 		int i;
 
-		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];
 
-			if (prev == ULONG_MAX)
-				prev = page->index - 1;
-			if (nr_to_write != LONG_MAX && page->index != prev + 1) {
-				pagevec_release(&pvec);
+			if (nr_to_write != LONG_MAX && i != 0 &&
+					folio->index != prev +
+					folio_nr_pages(fbatch.folios[i-1])) {
+				folio_batch_release(&fbatch);
 				goto stop;
 			}
 
-			lock_page(page);
+			folio_lock(folio);
 
-			if (unlikely(page->mapping != mapping)) {
+			if (unlikely(folio->mapping != mapping)) {
 continue_unlock:
-				unlock_page(page);
+				folio_unlock(folio);
 				continue;
 			}
-			if (!PageDirty(page)) {
+			if (!folio_test_dirty(folio)) {
 				/* someone wrote it for us */
 				goto continue_unlock;
 			}
 
-			f2fs_wait_on_page_writeback(page, META, true, true);
+			f2fs_wait_on_page_writeback(&folio->page, META,
+					true, true);
 
-			if (!clear_page_dirty_for_io(page))
+			if (!folio_clear_dirty_for_io(folio))
 				goto continue_unlock;
 
-			if (__f2fs_write_meta_page(page, &wbc, io_type)) {
-				unlock_page(page);
+			if (__f2fs_write_meta_page(&folio->page, &wbc,
+						io_type)) {
+				folio_unlock(folio);
 				break;
 			}
-			nwritten++;
-			prev = page->index;
+			nwritten += folio_nr_pages(folio);
+			prev = folio->index;
 			if (unlikely(nwritten >= nr_to_write))
 				break;
 		}
-		pagevec_release(&pvec);
+		folio_batch_release(&fbatch);
 		cond_resched();
 	}
 stop:
@@ -1403,7 +1406,7 @@ static void commit_checkpoint(struct f2fs_sb_info *sbi,
 	};
 
 	/*
-	 * pagevec_lookup_tag and lock_page again will take
+	 * filemap_get_folios_tag and lock_page again will take
 	 * some extra time. Therefore, f2fs_update_meta_pages and
 	 * f2fs_sync_meta_pages are combined in this function.
 	 */