1 files changed, 33 insertions, 20 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2074642..107da3d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2272,10 +2272,18 @@ int hugetlb_reserve_pages(struct inode *inode,
 					struct vm_area_struct *vma,
 					int acctflag)
 {
-	long ret = 0, chg;
+	long ret, chg;
 	struct hstate *h = hstate_inode(inode);
 
 	/*
+	 * 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;
+
+	/*
 	 * Shared mappings base their reservation on the number of pages that
 	 * are already allocated on behalf of the file. Private mappings need
 	 * to reserve the full area even if read-only as mprotect() may be
@@ -2283,42 +2291,47 @@ int hugetlb_reserve_pages(struct inode *inode,
 	 */
 	if (!vma || vma->vm_flags & VM_SHARED)
 		chg = region_chg(&inode->i_mapping->private_list, from, to);
-	else
+	else {
+		struct resv_map *resv_map = resv_map_alloc();
+		if (!resv_map)
+			return -ENOMEM;
+
 		chg = to - from;
 
+		set_vma_resv_map(vma, resv_map);
+		set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
+	}
+
 	if (chg < 0)
 		return chg;
 
+	/* There must be enough filesystem quota for the mapping */
 	if (hugetlb_get_quota(inode->i_mapping, chg))
 		return -ENOSPC;
 
 	/*
-	 * Only apply hugepage reservation if asked. We still have to
-	 * take the filesystem quota because it is an upper limit
-	 * defined for the mount and not necessarily memory as a whole
+	 * Check enough hugepages are available for the reservation.
+	 * Hand back the quota if there are not
 	 */
-	if (acctflag & VM_NORESERVE) {
-		reset_vma_resv_huge_pages(vma);
-		return 0;
-	}
-
 	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);
-	else {
-		struct resv_map *resv_map = resv_map_alloc();
-
-		if (!resv_map)
-			return -ENOMEM;
-
-		set_vma_resv_map(vma, resv_map);
-		set_vma_resv_flags(vma, HPAGE_RESV_OWNER);
-	}
-
 	return 0;
 }