fallocate hole punch will want to remove a specific range of
pages.  When pages are removed, their associated entries in
the region/reserve map will also be removed.  This will break
an assumption in the region_chg/region_add calling sequence.
If a new region descriptor must be allocated, it is done as
part of the region_chg processing.  In this way, region_add
can not fail because it does not need to attempt an allocation.

To prepare for fallocate hole punch, create a "cache" of
descriptors that can be used by region_add if necessary.
region_chg will ensure there are sufficient entries in the
cache.  It will be necessary to track the number of in progress
add operations to know a sufficient number of descriptors
reside in the cache.  A new routine region_abort is added to
adjust this in progress count when add operations are aborted.
vma_abort_reservation is also added for callers creating
reservations with vma_needs_reservation/vma_commit_reservation.

Signed-off-by: Mike Kravetz <redacted>
---
 include/linux/hugetlb.h |   3 +
 mm/hugetlb.c            | 169 ++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 153 insertions(+), 19 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index d891f94..667cf44 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h

@@ -35,6 +35,9 @@ struct resv_map {
 	struct kref refs;
 	spinlock_t lock;
 	struct list_head regions;
+	long adds_in_progress;
+	struct list_head rgn_cache;
+	long rgn_cache_count;
 };
 extern struct resv_map *resv_map_alloc(void);
 void resv_map_release(struct kref *ref);

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a8c3087..241d16d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c

@@ -240,11 +240,14 @@ struct file_region {
 
 /*
  * Add the huge page range represented by [f, t) to the reserve
- * map.  Existing regions will be expanded to accommodate the
- * specified range.  We know only existing regions need to be
- * expanded, because region_add is only called after region_chg
- * with the same range.  If a new file_region structure must
- * be allocated, it is done in region_chg.
+ * map.  In the normal case, existing regions will be expanded
+ * to accommodate the specified range.  Sufficient regions should
+ * exist for expansion due to the previous call to region_chg
+ * with the same range.  However, it is possible that region_del
+ * could have been called after region_chg and modifed the map
+ * in such a way that no region exists to be expanded.  In this
+ * case, pull a region descriptor from the cache associated with
+ * the map and use that for the new range.
  *
  * Return the number of new huge pages added to the map.  This
  * number is greater than or equal to zero.

@@ -261,6 +264,27 @@ static long region_add(struct resv_map *resv, long f, long t)
 		if (f <= rg->to)
 			break;
 
+	if (&rg->link == head || t < rg->from) {
+		/*
+		 * No region exists which can be expanded to include the
+		 * specified range.  Pull a region descriptor from the
+		 * cache, and use it for this range.
+		 */

@@ -3236,11 +3360,14 @@ retry:
 	 * any allocations necessary to record that reservation occur outside
 	 * the spinlock.
 	 */
-	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED))
+	if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {
 		if (vma_needs_reservation(h, vma, address) < 0) {
 			ret = VM_FAULT_OOM;
 			goto backout_unlocked;
 		}
+		/* Just decrements count, does not deallocate */
+		vma_abort_reservation(h, vma, address);
+	}

 
 	ptl = huge_pte_lockptr(h, mm, ptep);
 	spin_lock(ptl);

@@ -3387,6 +3514,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 			ret = VM_FAULT_OOM;
 			goto out_mutex;
 		}
+		/* Just decrements count, does not deallocate */
+		vma_abort_reservation(h, vma, address);
 
 		if (!(vma->vm_flags & VM_MAYSHARE))
 			pagecache_page = hugetlbfs_pagecache_page(h,

@@ -3726,6 +3855,8 @@ int hugetlb_reserve_pages(struct inode *inode,
 	}
 	return 0;
 out_err:
+	if (!vma || vma->vm_flags & VM_MAYSHARE)
+		region_abort(resv_map, from, to);
 	if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
 		kref_put(&resv_map->refs, resv_map_release);
 	return ret;

-- 
2.1.0