btrfs: convert end_compressed_writeback() to use filemap_get_folios()

Converted function 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.

Also this function does not care about the pages being contiguous so we
can just use filemap_get_folios() to be more efficient.

Link: https://lkml.kernel.org/r/20220824004023.77310-4-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/compression.c

@@ -8,6 +8,7 @@
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/pagemap.h>
+#include <linux/pagevec.h>
 #include <linux/highmem.h>
 #include <linux/kthread.h>
 #include <linux/time.h>
@@ -222,8 +223,7 @@ static noinline void end_compressed_writeback(struct inode *inode,
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	unsigned long index = cb->start >> PAGE_SHIFT;
 	unsigned long end_index = (cb->start + cb->len - 1) >> PAGE_SHIFT;
-	struct page *pages[16];
-	unsigned long nr_pages = end_index - index + 1;
+	struct folio_batch fbatch;
 	const int errno = blk_status_to_errno(cb->status);
 	int i;
 	int ret;
@@ -231,24 +231,23 @@ static noinline void end_compressed_writeback(struct inode *inode,
 	if (errno)
 		mapping_set_error(inode->i_mapping, errno);
 
-	while (nr_pages > 0) {
-		ret = find_get_pages_contig(inode->i_mapping, index,
-				     min_t(unsigned long,
-				     nr_pages, ARRAY_SIZE(pages)), pages);
-		if (ret == 0) {
-			nr_pages -= 1;
-			index += 1;
-			continue;
-		}
+	folio_batch_init(&fbatch);
+	while (index <= end_index) {
+		ret = filemap_get_folios(inode->i_mapping, &index, end_index,
+				&fbatch);
+
+		if (ret == 0)
+			return;
+
 		for (i = 0; i < ret; i++) {
+			struct folio *folio = fbatch.folios[i];
+
 			if (errno)
-				SetPageError(pages[i]);
-			btrfs_page_clamp_clear_writeback(fs_info, pages[i],
+				folio_set_error(folio);
+			btrfs_page_clamp_clear_writeback(fs_info, &folio->page,
 							 cb->start, cb->len);
-			put_page(pages[i]);
 		}
-		nr_pages -= ret;
-		index += ret;
+		folio_batch_release(&fbatch);
 	}
 	/* the inode may be gone now */
 }