mm: khugepaged: fix the incorrect statistics when collapsing large file folios

Khugepaged already supports collapsing file large folios (including shmem
mTHP) by commit 7de856f ("mm: khugepaged: support shmem mTHP
collapse"), and the control parameters in khugepaged:
'khugepaged_max_ptes_swap' and 'khugepaged_max_ptes_none', still compare
based on PTE granularity to determine whether a file collapse is needed. 
However, the statistics for 'present' and 'swap' in
hpage_collapse_scan_file() do not take into account the large folios,
which may lead to incorrect judgments regarding the
khugepaged_max_ptes_swap/none parameters, resulting in unnecessary file
collapses.

To fix this issue, take into account the large folios' statistics for
'present' and 'swap' variables in the hpage_collapse_scan_file().

Link: https://lkml.kernel.org/r/c76305d96d12d030a1a346b50503d148364246d2.1728901391.git.baolin.wang@linux.alibaba.com
Fixes: 7de856f ("mm: khugepaged: support shmem mTHP collapse")
Signed-off-by: Baolin Wang <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Barry Song <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Reviewed-by: Yang Shi <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Ryan Roberts <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Baolin Wang

mm/khugepaged.c

@@ -2252,7 +2252,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
 			continue;
 
 		if (xa_is_value(folio)) {
-			++swap;
+			swap += 1 << xas_get_order(&xas);
 			if (cc->is_khugepaged &&
 			    swap > khugepaged_max_ptes_swap) {
 				result = SCAN_EXCEED_SWAP_PTE;
@@ -2299,7 +2299,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
 		 * is just too costly...
 		 */
 
-		present++;
+		present += folio_nr_pages(folio);
 
 		if (need_resched()) {
 			xas_pause(&xas);