[PATCH v2 4/5] mm,hugetlb: Drop obsolete comment about non-present pte and second faults

Oscar Salvador
2025-06-20T12:30:40Z

There is a comment in hugetlb_fault() that does not hold anymore.
This one:

/*
* vmf.orig_pte could be a migration/hwpoison vmf.orig_pte at this
* point, so this check prevents the kernel from going below assuming
* that we have an active hugepage in pagecache. This goto expects
* the 2nd page fault, and is_hugetlb_entry_(migration|hwpoisoned)
* check will properly handle it.
*/

This was written because back in the day we used to do:

hugetlb_fault () {
ptep = huge_pte_offset(...)
if (ptep) {
entry = huge_ptep_get(ptep)
if (unlikely(is_hugetlb_entry_migration(entry))
...
else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
...
}

...
...

/*
* entry could be a migration/hwpoison entry at this point, so this
* check prevents the kernel from going below assuming that we have
* a active hugepage in pagecache. This goto expects the 2nd page fault,
* and is_hugetlb_entry_(migration|hwpoisoned) check will properly
* handle it.
*/
if (!pte_present(entry))
goto out_mutex;
...
}

The code was designed to check for hwpoisoned/migration entries upfront,
and then bail out if further down the pte was not present anymore,
relying on the second fault to properly handle migration/hwpoison entries that
time around.

The way we handle this is different nowadays, so drop the misleading comment.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
mm/hugetlb.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 57bb8b2dce21..868ee8ed45c0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6746,13 +6746,7 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,

ret = 0;

- /*
- * vmf.orig_pte could be a migration/hwpoison vmf.orig_pte at this
- * point, so this check prevents the kernel from going below assuming
- * that we have an active hugepage in pagecache. This goto expects
- * the 2nd page fault, and is_hugetlb_entry_(migration|hwpoisoned)
- * check will properly handle it.
- */
+ /* Not present, either a migration or a hwpoisoned entry */
if (!pte_present(vmf.orig_pte)) {
if (unlikely(is_hugetlb_entry_migration(vmf.orig_pte))) {
/*
--
2.50.0