mm/vmscan: Account large folios correctly

The statistics we gather should count the number of pages, not the
number of folios.  The logic in this function is somewhat convoluted,
but even if we split the folio, I think the accounting is now correct.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

Author: Matthew Wilcox (Oracle)

mm/vmscan.c

@@ -1575,10 +1575,10 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 		 */
 		folio_check_dirty_writeback(folio, &dirty, &writeback);
 		if (dirty || writeback)
-			stat->nr_dirty++;
+			stat->nr_dirty += nr_pages;
 
 		if (dirty && !writeback)
-			stat->nr_unqueued_dirty++;
+			stat->nr_unqueued_dirty += nr_pages;
 
 		/*
 		 * Treat this page as congested if the underlying BDI is or if
@@ -1590,7 +1590,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 		if (((dirty || writeback) && mapping &&
 		     inode_write_congested(mapping->host)) ||
 		    (writeback && PageReclaim(page)))
-			stat->nr_congested++;
+			stat->nr_congested += nr_pages;
 
 		/*
 		 * If a page at the tail of the LRU is under writeback, there
@@ -1639,7 +1639,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 			if (current_is_kswapd() &&
 			    PageReclaim(page) &&
 			    test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
-				stat->nr_immediate++;
+				stat->nr_immediate += nr_pages;
 				goto activate_locked;
 
 			/* Case 2 above */
@@ -1657,7 +1657,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 				 * and it's also appropriate in global reclaim.
 				 */
 				SetPageReclaim(page);
-				stat->nr_writeback++;
+				stat->nr_writeback += nr_pages;
 				goto activate_locked;
 
 			/* Case 3 above */
@@ -1823,7 +1823,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 			case PAGE_ACTIVATE:
 				goto activate_locked;
 			case PAGE_SUCCESS:
-				stat->nr_pageout += thp_nr_pages(page);
+				stat->nr_pageout += nr_pages;
 
 				if (PageWriteback(page))
 					goto keep;