mm: free folios in a batch in shrink_folio_list()

Use free_unref_page_batch() to free the folios.  This may increase the
number of IPIs from calling try_to_unmap_flush() more often, but that's
going to be very workload-dependent.  It may even reduce the number of
IPIs as we now batch-free large folios instead of freeing them one at a
time.

Link: https://lkml.kernel.org/r/20240227174254.710559-12-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -1006,14 +1006,15 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 		struct pglist_data *pgdat, struct scan_control *sc,
 		struct reclaim_stat *stat, bool ignore_references)
 {
+	struct folio_batch free_folios;
 	LIST_HEAD(ret_folios);
-	LIST_HEAD(free_folios);
 	LIST_HEAD(demote_folios);
 	unsigned int nr_reclaimed = 0;
 	unsigned int pgactivate = 0;
 	bool do_demote_pass;
 	struct swap_iocb *plug = NULL;
 
+	folio_batch_init(&free_folios);
 	memset(stat, 0, sizeof(*stat));
 	cond_resched();
 	do_demote_pass = can_demote(pgdat->node_id, sc);
@@ -1412,14 +1413,11 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 		 */
 		nr_reclaimed += nr_pages;
 
-		/*
-		 * Is there need to periodically free_folio_list? It would
-		 * appear not as the counts should be low
-		 */
-		if (unlikely(folio_test_large(folio)))
-			destroy_large_folio(folio);
-		else
-			list_add(&folio->lru, &free_folios);
+		if (folio_batch_add(&free_folios, folio) == 0) {
+			mem_cgroup_uncharge_folios(&free_folios);
+			try_to_unmap_flush();
+			free_unref_folios(&free_folios);
+		}
 		continue;
 
 activate_locked_split:
@@ -1483,9 +1481,9 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
 
 	pgactivate = stat->nr_activate[0] + stat->nr_activate[1];
 
-	mem_cgroup_uncharge_list(&free_folios);
+	mem_cgroup_uncharge_folios(&free_folios);
 	try_to_unmap_flush();
-	free_unref_page_list(&free_folios);
+	free_unref_folios(&free_folios);
 
 	list_splice(&ret_folios, folio_list);
 	count_vm_events(PGACTIVATE, pgactivate);