In vma_has_reserves(), the current assumption is that reserves are
always present for shared mappings. However, this will not be the
case with fallocate hole punch. When punching a hole, the present
page will be deleted as well as the region/reserve map entry (and
hence any reservation). vma_has_reserves is passed "chg" which
indicates whether or not a region/reserve map is present. Use
this to determine if reserves are actually present or were removed
via hole punch.
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
mm/hugetlb.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1c3049c..5923c21 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -800,9 +800,19 @@ static int vma_has_reserves(struct vm_area_struct *vma, long chg)
return 0;
}
- /* Shared mappings always use reserves */
- if (vma->vm_flags & VM_MAYSHARE)
- return 1;
+ if (vma->vm_flags & VM_MAYSHARE) {
+ /*
+ * We know VM_NORESERVE is not set. Therefore, there SHOULD
+ * be a region map for all pages. The only situation where
+ * there is no region map is if a hole was punched via
+ * fallocate. In this case, there really are no reverves to
+ * use. This situation is indicated if chg != 0.
+ */
+ if (chg)
+ return 0;
+ else
+ return 1;
+ }
/*
* Only the process that called mmap() has reserves for
--
2.1.0
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