On 07/02/2015 09:21 PM, Hillf Danton wrote:

quoted

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            | 166 ++++++++++++++++++++++++++++++++++++++++++------
  2 files changed, 150 insertions(+), 19 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 2050261..f9c8cb2 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..189c0d7 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 exits which can be expanded to include the

s/exits/exists/ ?

Yes, that is a typo and should be exists.

quoted

+		 * specified range.  Pull a region descriptor from the
+		 * cache, and use it for this range.
+		 */
+		VM_BUG_ON(!resv->rgn_cache_count);
+
+		resv->rgn_cache_count--;
+		nrg = list_first_entry(&resv->rgn_cache, struct file_region,
+					link);
+		list_del(&nrg->link);
+
+		nrg->from = f;
+		nrg->to = t;
+		list_add(&nrg->link, rg->link.prev);
+
+		add += t - f;
+		goto out_locked;
+	}
+
  	/* Round our left edge to the current segment if it encloses us. */
  	if (f > rg->from)
  		f = rg->from;

@@ -294,6 +318,8 @@ static long region_add(struct resv_map *resv, long f, long t)
  	add += t - nrg->to;		/* Added to end of region */
  	nrg->to = t;

+out_locked:
+	resv->adds_in_progress--;
  	spin_unlock(&resv->lock);
  	VM_BUG_ON(add < 0);
  	return add;

@@ -312,11 +338,16 @@ static long region_add(struct resv_map *resv, long f, long t)
   * so that the subsequent region_add call will have all the
   * regions it needs and will not fail.
   *
+ * Upon entry, region_chg will also examine the cache of
+ * region descriptors associated with the map.  If there
+ * not enough descriptors cached, one will be allocated
+ * for the in progress add operation.
+ *
   * Returns the number of huge pages that need to be added
   * to the existing reservation map for the range [f, t).
   * This number is greater or equal to zero.  -ENOMEM is
- * returned if a new file_region structure is needed and can
- * not be allocated.
+ * returned if a new file_region structure or cache entry
+ * is needed and can not be allocated.
   */
  static long region_chg(struct resv_map *resv, long f, long t)
  {

@@ -326,6 +357,30 @@ static long region_chg(struct resv_map *resv, long f, long t)

  retry:
  	spin_lock(&resv->lock);
+	resv->adds_in_progress++;
+
+	/*
+	 * Check for sufficient descriptors in the cache to accommodate
+	 * the number of in progress add operations.
+	 */
+	if (resv->adds_in_progress > resv->rgn_cache_count) {
+		struct file_region *trg;
+
+		VM_BUG_ON(resv->adds_in_progress - resv->rgn_cache_count > 1);
+		/* Must drop lock to allocate a new descriptor. */
+		resv->adds_in_progress--;
+		spin_unlock(&resv->lock);
+
+		trg = kmalloc(sizeof(*trg), GFP_KERNEL);
+		if (!trg)
+			return -ENOMEM;
+
+		spin_lock(&resv->lock);
+		resv->adds_in_progress++;
+		list_add(&trg->link, &resv->rgn_cache);
+		resv->rgn_cache_count++;
+	}
+
  	/* Locate the region we are before or in. */
  	list_for_each_entry(rg, head, link)
  		if (f <= rg->to)

@@ -336,6 +391,7 @@ retry:
  	 * size such that we can guarantee to record the reservation. */
  	if (&rg->link == head || t < rg->from) {
  		if (!nrg) {
+			resv->adds_in_progress--;
  			spin_unlock(&resv->lock);
  			nrg = kmalloc(sizeof(*nrg), GFP_KERNEL);
  			if (!nrg)

@@ -385,6 +441,25 @@ out_nrg:
  }

  /*
+ * Abort the in progress add operation.  The adds_in_progress field
+ * of the resv_map keeps track of the operations in progress between
+ * calls to region_chg and region_add.  Operations are sometimes
+ * aborted after the call to region_chg.  In such cases, region_abort
+ * is called to decrement the adds_in_progress counter.
+ *
+ * NOTE: The range arguments [f, t) are not needed or used in this
+ * routine.  They are kept to make reading the calling code easier as
+ * arguments will match the associated region_chg call.
+ */
+static void region_abort(struct resv_map *resv, long f, long t)
+{
+	spin_lock(&resv->lock);
+	VM_BUG_ON(!resv->rgn_cache_count);
+	resv->adds_in_progress--;
+	spin_unlock(&resv->lock);
+}
+
+/*
   * Truncate the reserve map at index 'end'.  Modify/truncate any
   * region which contains end.  Delete any regions past end.
   * Return the number of huge pages removed from the map.

@@ -544,22 +619,42 @@ static void set_vma_private_data(struct vm_area_struct *vma,
  struct resv_map *resv_map_alloc(void)
  {
  	struct resv_map *resv_map = kmalloc(sizeof(*resv_map), GFP_KERNEL);
-	if (!resv_map)
+	struct file_region *rg = kmalloc(sizeof(*rg), GFP_KERNEL);
+
+	if (!resv_map || !rg) {
+		kfree(resv_map);
+		kfree(rg);
  		return NULL;
+	}

  	kref_init(&resv_map->refs);
  	spin_lock_init(&resv_map->lock);
  	INIT_LIST_HEAD(&resv_map->regions);

+	resv_map->adds_in_progress = 0;
+
+	INIT_LIST_HEAD(&resv_map->rgn_cache);
+	list_add(&rg->link, &resv_map->rgn_cache);
+	resv_map->rgn_cache_count = 1;
+
  	return resv_map;
  }

  void resv_map_release(struct kref *ref)
  {
  	struct resv_map *resv_map = container_of(ref, struct resv_map, refs);
+	struct list_head *head = &resv_map->regions;
+	struct file_region *rg, *trg;

  	/* Clear out any active regions before we release the map. */
  	region_truncate(resv_map, 0);
+
+	/* ... and any entries left in the cache */
+	list_for_each_entry_safe(rg, trg, head, link)
+		list_del(&rg->link);
+

I am wondering if `cache' is rgn_cache.
And rg should be freed if yes.

Good catch.

It should be:

	struct list_head *head = &resv_map->rgn_cache;

and

	list_for_each_entry_safe(rg, trg, head, link) {
		list_del(&rg->link);
		kfree(rg);
	}

As is, it will leak memory and not free entries in the cache.

I will fix this in the next revision.

-- 
Mike Kravetz

quoted

+	VM_BUG_ON(resv_map->adds_in_progress);
+
  	kfree(resv_map);
  }

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