ceph: use pagevec_lookup_range_nr_tag()

Use new function for looking up pages since nr_pages argument from
pagevec_lookup_range_tag() is going away.

Link: http://lkml.kernel.org/r/20171009151359.31984-14-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ceph/addr.c

@@ -783,8 +783,7 @@ retry:
 		struct page **pages = NULL;
 		mempool_t *pool = NULL;	/* Becomes non-null if mempool used */
 		struct page *page;
-		int want;
-		u64 offset, len;
+		u64 offset = 0, len = 0;
 		long writeback_stat;
 
 		next = 0;
@@ -793,13 +792,9 @@ retry:
 
 get_more_pages:
 		first = -1;
-		want = min(end - index,
-			   min((pgoff_t)PAGEVEC_SIZE,
-			       max_pages - (pgoff_t)locked_pages) - 1)
-			+ 1;
 		pvec_pages = pagevec_lookup_range_tag(&pvec, mapping, &index,
 						end, PAGECACHE_TAG_DIRTY,
-						want);
+						max_pages - locked_pages);
 		dout("pagevec_lookup_range_tag got %d\n", pvec_pages);
 		if (!pvec_pages && !locked_pages)
 			break;