Date:	Wed,  8 Jul 2015 17:21:32 -0700
From:	Mike Kravetz <mike.kravetz@...cle.com>
To:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Cc:	Dave Hansen <dave.hansen@...ux.intel.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH v2 01/10] mm/hugetlb: add cache of descriptors to resv_map for region_add

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 <mike.kravetz@...cle.com>
---
 include/linux/hugetlb.h |   3 +
 mm/hugetlb.c            | 168 ++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 152 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..de03374 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.
+		 */
+		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 +619,44 @@ 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->rgn_cache;
+	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);
+		kfree(rg);
+	}
+
+	VM_BUG_ON(resv_map->adds_in_progress);
+
 	kfree(resv_map);
 }
 
@@ -1473,16 +1570,18 @@ static void return_unused_surplus_pages(struct hstate *h,
 	}
 }
 
+
 /*
- * vma_needs_reservation and vma_commit_reservation are used by the huge
- * page allocation routines to manage reservations.
+ * vma_needs_reservation, vma_commit_reservation and vma_abort_reservation
+ * are used by the huge page allocation routines to manage reservations.
  *
  * vma_needs_reservation is called to determine if the huge page at addr
  * within the vma has an associated reservation.  If a reservation is
  * needed, the value 1 is returned.  The caller is then responsible for
  * managing the global reservation and subpool usage counts.  After
  * the huge page has been allocated, vma_commit_reservation is called
- * to add the page to the reservation map.
+ * to add the page to the reservation map.  If the reservation must be
+ * aborted instead of committed, vma_abort_reservation is called.
  *
  * In the normal case, vma_commit_reservation returns the same value
  * as the preceding vma_needs_reservation call.  The only time this
@@ -1490,9 +1589,14 @@ static void return_unused_surplus_pages(struct hstate *h,
  * is the responsibility of the caller to notice the difference and
  * take appropriate action.
  */
+enum vma_resv_mode {
+	VMA_NEEDS_RESV,
+	VMA_COMMIT_RESV,
+	VMA_ABORT_RESV,
+};
 static long __vma_reservation_common(struct hstate *h,
 				struct vm_area_struct *vma, unsigned long addr,
-				bool commit)
+				enum vma_resv_mode mode)
 {
 	struct resv_map *resv;
 	pgoff_t idx;
@@ -1503,10 +1607,20 @@ static long __vma_reservation_common(struct hstate *h,
 		return 1;
 
 	idx = vma_hugecache_offset(h, vma, addr);
-	if (commit)
-		ret = region_add(resv, idx, idx + 1);
-	else
+	switch (mode) {
+	case VMA_NEEDS_RESV:
 		ret = region_chg(resv, idx, idx + 1);
+		break;
+	case VMA_COMMIT_RESV:
+		ret = region_add(resv, idx, idx + 1);
+		break;
+	case VMA_ABORT_RESV:
+		region_abort(resv, idx, idx + 1);
+		ret = 0;
+		break;
+	default:
+		BUG();
+	}
 
 	if (vma->vm_flags & VM_MAYSHARE)
 		return ret;
@@ -1517,13 +1631,19 @@ static long __vma_reservation_common(struct hstate *h,
 static long vma_needs_reservation(struct hstate *h,
 			struct vm_area_struct *vma, unsigned long addr)
 {
-	return __vma_reservation_common(h, vma, addr, false);
+	return __vma_reservation_common(h, vma, addr, VMA_NEEDS_RESV);
 }
 
 static long vma_commit_reservation(struct hstate *h,
 			struct vm_area_struct *vma, unsigned long addr)
 {
-	return __vma_reservation_common(h, vma, addr, true);
+	return __vma_reservation_common(h, vma, addr, VMA_COMMIT_RESV);
+}
+
+static void vma_abort_reservation(struct hstate *h,
+			struct vm_area_struct *vma, unsigned long addr)
+{
+	(void)__vma_reservation_common(h, vma, addr, VMA_ABORT_RESV);
 }
 
 static struct page *alloc_huge_page(struct vm_area_struct *vma,
@@ -1549,8 +1669,10 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
 	if (chg < 0)
 		return ERR_PTR(-ENOMEM);
 	if (chg || avoid_reserve)
-		if (hugepage_subpool_get_pages(spool, 1) < 0)
+		if (hugepage_subpool_get_pages(spool, 1) < 0) {
+			vma_abort_reservation(h, vma, addr);
 			return ERR_PTR(-ENOSPC);
+		}
 
 	ret = hugetlb_cgroup_charge_cgroup(idx, pages_per_huge_page(h), &h_cg);
 	if (ret)
@@ -1596,6 +1718,7 @@ out_uncharge_cgroup:
 out_subpool_put:
 	if (chg || avoid_reserve)
 		hugepage_subpool_put_pages(spool, 1);
+	vma_abort_reservation(h, vma, addr);
 	return ERR_PTR(-ENOSPC);
 }
 
@@ -3236,11 +3359,14 @@ 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 +3513,8 @@ 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 +3854,8 @@ 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

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