btrfs: convert __process_pages_contig() to use filemap_get_folios_contig()

Convert to use folios throughout.  This is in preparation for the removal
of find_get_pages_contig().  Now also supports large folios.

Since we may receive more than nr_pages pages, nr_pages may underflow. 
Since nr_pages > 0 is equivalent to index <= end_index, we replaced it
with this check instead.

Link: https://lkml.kernel.org/r/20220824004023.77310-3-vishal.moola@gmail.comSigned-off-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Acked-by: David Sterba <dsterba@suse.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Chris Mason <clm@fb.com>
Cc: David Sterba <dsterb@suse.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/btrfs/extent_io.c

@@ -1900,9 +1900,8 @@ static int __process_pages_contig(struct address_space *mapping,
 	pgoff_t start_index = start >> PAGE_SHIFT;
 	pgoff_t end_index = end >> PAGE_SHIFT;
 	pgoff_t index = start_index;
-	unsigned long nr_pages = end_index - start_index + 1;
 	unsigned long pages_processed = 0;
-	struct page *pages[16];
+	struct folio_batch fbatch;
 	int err = 0;
 	int i;
 
@@ -1911,16 +1910,17 @@ static int __process_pages_contig(struct address_space *mapping,
 		ASSERT(processed_end && *processed_end == start);
 	}
 
-	if ((page_ops & PAGE_SET_ERROR) && nr_pages > 0)
+	if ((page_ops & PAGE_SET_ERROR) && start_index <= end_index)
 		mapping_set_error(mapping, -EIO);
 
-	while (nr_pages > 0) {
-		int found_pages;
+	folio_batch_init(&fbatch);
+	while (index <= end_index) {
+		int found_folios;
+
+		found_folios = filemap_get_folios_contig(mapping, &index,
+				end_index, &fbatch);
 
-		found_pages = find_get_pages_contig(mapping, index,
-				     min_t(unsigned long,
-				     nr_pages, ARRAY_SIZE(pages)), pages);
-		if (found_pages == 0) {
+		if (found_folios == 0) {
 			/*
 			 * Only if we're going to lock these pages, we can find
 			 * nothing at @index.
@@ -1930,23 +1930,20 @@ static int __process_pages_contig(struct address_space *mapping,
 			goto out;
 		}
 
-		for (i = 0; i < found_pages; i++) {
+		for (i = 0; i < found_folios; i++) {
 			int process_ret;
-
+			struct folio *folio = fbatch.folios[i];
 			process_ret = process_one_page(fs_info, mapping,
-					pages[i], locked_page, page_ops,
+					&folio->page, locked_page, page_ops,
 					start, end);
 			if (process_ret < 0) {
-				for (; i < found_pages; i++)
-					put_page(pages[i]);
 				err = -EAGAIN;
+				folio_batch_release(&fbatch);
 				goto out;
 			}
-			put_page(pages[i]);
-			pages_processed++;
+			pages_processed += folio_nr_pages(folio);
 		}
-		nr_pages -= found_pages;
-		index += found_pages;
+		folio_batch_release(&fbatch);
 		cond_resched();
 	}
 out: