The current code would unnecessarily expand the address range. Consider
one example, (start, end) = (1G-2M, 3G+2M), and (vm_start, vm_end) =
(1G-4M, 3G+4M), the expected adjustment should be keep (1G-2M, 3G+2M)
without expand. But the current result will be (1G-4M, 3G+4M). Actually,
the range (1G-4M, 1G) and (3G, 3G+4M) would never been involved in pmd
sharing.
After this patch, if pud aligned *start across vm_start, then we know the
*start and vm_start are in same pud_index, and vm_start is not pud
aligned, so don't adjust *start. Same logic applied to *end.
Fixes: commit 75802ca66354 ("mm/hugetlb: fix calculation of adjust_range_if_pmd_sharing_possible")
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Signed-off-by: Li Xinhai <lixinhai.lxh@xxxxxxxxx>
---
mm/hugetlb.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index cbf32d2824fd..d1e9ea55b7e6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5249,11 +5249,16 @@ void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
a_end = ALIGN(*end, PUD_SIZE);
/*
- * Intersect the range with the vma range, since pmd sharing won't be
- * across vma after all
+ * If the PUD aligned address across vma range, then it means the
+ * vm_start/vm_end is not PUD aligned. In that case, we must don't
+ * adjust range because pmd sharing is not possbile at the start and/or
+ * end part of vma.
*/
- *start = max(vma->vm_start, a_start);
- *end = min(vma->vm_end, a_end);
+ if (a_start >= vma->vm_start)
+ *start = a_start;
+
+ if (a_end <= vma->vm_end)
+ *end = a_end;
}
/*
--
2.18.4
