1 files changed, 26 insertions, 2 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 618e98304080..107da3d809a8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2269,12 +2269,18 @@ void hugetlb_change_protection(struct vm_area_struct *vma,
 
 int hugetlb_reserve_pages(struct inode *inode,
                                         long from, long to,
-                                        struct vm_area_struct *vma)
+                                        struct vm_area_struct *vma,
+                                        int acctflag)
 {
         long ret, chg;
         struct hstate *h = hstate_inode(inode);
 
-        if (vma && vma->vm_flags & VM_NORESERVE)
+        /*
+         * Only apply hugepage reservation if asked. At fault time, an
+         * attempt will be made for VM_NORESERVE to allocate a page
+         * and filesystem quota without using reserves
+         */
+        if (acctflag & VM_NORESERVE)
                 return 0;
 
         /*
@@ -2299,13 +2305,31 @@ int hugetlb_reserve_pages(struct inode *inode,
         if (chg < 0)
                 return chg;
 
+        /* There must be enough filesystem quota for the mapping */
         if (hugetlb_get_quota(inode->i_mapping, chg))
                 return -ENOSPC;
+
+        /*
+         * Check enough hugepages are available for the reservation.
+         * Hand back the quota if there are not
+         */
         ret = hugetlb_acct_memory(h, chg);
         if (ret < 0) {
                 hugetlb_put_quota(inode->i_mapping, chg);
                 return ret;
         }
+
+        /*
+         * Account for the reservations made. Shared mappings record regions
+         * that have reservations as they are shared by multiple VMAs.
+         * When the last VMA disappears, the region map says how much
+         * the reservation was and the page cache tells how much of
+         * the reservation was consumed. Private mappings are per-VMA and
+         * only the consumed reservations are tracked. When the VMA
+         * disappears, the original reservation is the VMA size and the
+         * consumed reservations are stored in the map. Hence, nothing
+         * else has to be done for private mappings here
+         */
         if (!vma || vma->vm_flags & VM_SHARED)
                 region_add(&inode->i_mapping->private_list, from, to);
         return 0;