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

Khugepaged already supports collapsing file large folios (including shmem
mTHP) by commit 7de856ffd007 ("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: 7de856ffd007 ("mm: khugepaged: support shmem mTHP collapse")
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index a420eff92011e878da441d92299bb9b9e1457c52..b538c3d48386a57f98b68899f6fc45f509af596f 100644 (file)
--- a/mm/khugepaged.c
+++ b/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);