In collapse_file(), after locking the page, it is necessary to recheck
that the page is up-to-date. Add PageUptodate() check for both shmem THP
and file THP.
Current khugepaged should not try to collapse dirty file THP, because it
is limited to read only text. Add a PageDirty check and warning for file
THP. This is added after page_mapping() check, because if the page is
truncated, it might be dirty.
Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
Changes v1 => v2:
Rearrange the checks per feedback from Johannes, Rik, and Kirill.
---
mm/khugepaged.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 0a1b4b484ac5..40c549302d36 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1626,7 +1626,12 @@ static void collapse_file(struct mm_struct *mm,
* without racing with truncate.
*/
VM_BUG_ON_PAGE(!PageLocked(page), page);
- VM_BUG_ON_PAGE(!PageUptodate(page), page);
+
+ /* double check the page is up to date */
+ if (unlikely(!PageUptodate(page))) {
+ result = SCAN_FAIL;
+ goto out_unlock;
+ }
/*
* If file was truncated then extended, or hole-punched, before
@@ -1642,6 +1647,15 @@ static void collapse_file(struct mm_struct *mm,
goto out_unlock;
}
+ /*
+ * khugepaged should not try to collapse dirty pages for
+ * file THP. Show warning if this somehow happens.
+ */
+ if (WARN_ON_ONCE(!is_shmem && PageDirty(page))) {
+ result = SCAN_FAIL;
+ goto out_unlock;
+ }
+
if (isolate_lru_page(page)) {
result = SCAN_DEL_PAGE_LRU;
goto out_unlock;
--
2.17.1
