mm/vmscan: take all base pages of THP into account when race with speculative reference

If the page has buffers, shrink_page_list will try to free the buffer
mappings associated with the page and try to free the page as well.  In
the rare race with speculative reference, the page will be freed shortly
by speculative reference.  But nr_reclaimed is not incremented correctly
when we come across the THP.  We need to account all the base pages in
this case.

Link: https://lkml.kernel.org/r/20220425111232.23182-5-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Huang, Ying <ying.huang@intel.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/vmscan.c

@@ -1884,7 +1884,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 					 * increment nr_reclaimed here (and
 					 * leave it off the LRU).
 					 */
-					nr_reclaimed++;
+					nr_reclaimed += nr_pages;
 					continue;
 				}
 			}