mm/hugetlb: vma_has_reserves() needs to handle fallocate hole punch

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 <[email protected]>
Reviewed-by: Naoya Horiguchi <[email protected]>
Acked-by: Hillf Danton <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Aneesh Kumar <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Michal Hocko <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 61c52cd5f77b775e82bf508b7550742bae06a709..bd12e8c8bc7b4702c8d31c37b4a2250959099af6 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -801,8 +801,19 @@ static bool vma_has_reserves(struct vm_area_struct *vma, long chg)
        }
 
        /* Shared mappings always use reserves */
-       if (vma->vm_flags & VM_MAYSHARE)
-               return true;
+       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 false;
+               else
+                       return true;
+       }
 
        /*
         * Only the process that called mmap() has reserves for