mm: pagevec: add folio_batch_reinit()

Patch series "update mlock to use folios", v4.

This series updates mlock to use folios, converting the internal interface
to using folios exclusively and exposing the folio interface externally.

As a product of this we move to using a folio batch rather than a pagevec
for mlock folios, which brings it in line with the core folio batches
contained in mm/swap.c.


This patch (of 5):

This performs the same task as pagevec_reinit(), only modifying a folio
batch rather than a pagevec.

Link: https://lkml.kernel.org/r/cover.1673526881.git.lstoakes@gmail.com
Link: https://lkml.kernel.org/r/9018cecacb39e34c883540f997f9be8281153613.1673526881.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/pagevec.h

@@ -103,6 +103,11 @@ static inline void folio_batch_init(struct folio_batch *fbatch)
 	fbatch->percpu_pvec_drained = false;
 }
 
+static inline void folio_batch_reinit(struct folio_batch *fbatch)
+{
+	fbatch->nr = 0;
+}
+
 static inline unsigned int folio_batch_count(struct folio_batch *fbatch)
 {
 	return fbatch->nr;