mm: add variant of pagevec_lookup_range_tag() taking number of pages

Currently pagevec_lookup_range_tag() takes number of pages to look up
but most users don't need this.  Create a new function
pagevec_lookup_range_nr_tag() that takes maximum number of pages to
lookup for Ceph which wants this functionality so that we can drop
nr_pages argument from pagevec_lookup_range_tag().

Link: http://lkml.kernel.org/r/20171009151359.31984-13-jack@suse.cz
Signed-off-by: Jan Kara <jack@suse.cz>
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>

include/linux/pagevec.h

@@ -41,6 +41,9 @@ static inline unsigned pagevec_lookup(struct pagevec *pvec,
 unsigned pagevec_lookup_range_tag(struct pagevec *pvec,
 		struct address_space *mapping, pgoff_t *index, pgoff_t end,
 		int tag, unsigned nr_pages);
+unsigned pagevec_lookup_range_nr_tag(struct pagevec *pvec,
+		struct address_space *mapping, pgoff_t *index, pgoff_t end,
+		int tag, unsigned max_pages);
 static inline unsigned pagevec_lookup_tag(struct pagevec *pvec,
 		struct address_space *mapping, pgoff_t *index, int tag,
 		unsigned nr_pages)

mm/swap.c

@@ -996,6 +996,15 @@ unsigned pagevec_lookup_range_tag(struct pagevec *pvec,
 }
 EXPORT_SYMBOL(pagevec_lookup_range_tag);
 
+unsigned pagevec_lookup_range_nr_tag(struct pagevec *pvec,
+		struct address_space *mapping, pgoff_t *index, pgoff_t end,
+		int tag, unsigned max_pages)
+{
+	pvec->nr = find_get_pages_range_tag(mapping, index, end, tag,
+		min_t(unsigned int, max_pages, PAGEVEC_SIZE), pvec->pages);
+	return pagevec_count(pvec);
+}
+EXPORT_SYMBOL(pagevec_lookup_range_nr_tag);
 /*
  * Perform any setup for the swap system
  */