[PATCH 03/35] dmem: implement dmem memory management

From: yulei.kernel@gmail.com
To: akpm@linux-foundation.org, naoya.horiguchi@nec.com,
	viro@zeniv.linux.org.uk, pbonzini@redhat.com
Cc: linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, xiaoguangrong.eric@gmail.com,
	kernellwp@gmail.com, lihaiwei.kernel@gmail.com,
	Yulei Zhang <yuleixzhang@tencent.com>,
	Xiao Guangrong <gloryxiao@tencent.com>
Subject: [PATCH 03/35] dmem: implement dmem memory management
Date: Thu,  8 Oct 2020 15:53:53 +0800	[thread overview]
Message-ID: <57408f6bd8122d915e46deed96a20a8ac6d90d9f.1602093760.git.yuleixzhang@tencent.com> (raw)
In-Reply-To: <cover.1602093760.git.yuleixzhang@tencent.com>
In-Reply-To: <cover.1602093760.git.yuleixzhang@tencent.com>

From: Yulei Zhang <yuleixzhang@tencent.com>

It introduces the interfaces to manage dmem pages that include:
  - dmem_region_register(), it registers the reserved memory to the
    dmem management system, later it can be allocated out for dmemfs

 - dmem_alloc_init(), initiate dmem allocator, note the page size the
   allocator used isn't the same thing with the alignment used to
   reserve dmem memory

 - dmem_alloc_pages_from_vma() and dmem_free_pages() are the interfaces
   allocating and freeing dmem memory, multiple pages can be allocated
   at one time, but it should be power of two

Signed-off-by: Xiao Guangrong <gloryxiao@tencent.com>
Signed-off-by: Yulei Zhang <yuleixzhang@tencent.com>
---
 include/linux/dmem.h |   3 +
 mm/dmem.c            | 674 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 677 insertions(+)

diff --git a/include/linux/dmem.h b/include/linux/dmem.h
index 5049322d941c..476a82e8f252 100644
--- a/include/linux/dmem.h
+++ b/include/linux/dmem.h
@@ -7,6 +7,9 @@ int dmem_reserve_init(void);
 void dmem_init(void);
 int dmem_region_register(int node, phys_addr_t start, phys_addr_t end);
 
+int dmem_alloc_init(unsigned long dpage_shift);
+void dmem_alloc_uinit(void);
+
 #else
 static inline int dmem_reserve_init(void)
 {
diff --git a/mm/dmem.c b/mm/dmem.c
index b5fb4f1b92db..a77a064c8d59 100644
--- a/mm/dmem.c
+++ b/mm/dmem.c
@@ -91,11 +91,38 @@ static struct dmem_pool dmem_pool = {
 	.lock = __MUTEX_INITIALIZER(dmem_pool.lock),
 };
 
+#define DMEM_PAGE_SIZE		(1UL << dmem_pool.dpage_shift)
+#define DMEM_PAGE_UP(x)		phys_to_dpage(((x) + DMEM_PAGE_SIZE - 1))
+#define DMEM_PAGE_DOWN(x)	phys_to_dpage(x)
+
+#define dpage_to_phys(_dpage)						\
+	((_dpage) << dmem_pool.dpage_shift)
+#define phys_to_dpage(_addr)						\
+	((_addr) >> dmem_pool.dpage_shift)
+
+#define dpage_to_pfn(_dpage)						\
+	(__phys_to_pfn(dpage_to_phys(_dpage)))
+#define pfn_to_dpage(_pfn)						\
+	(phys_to_dpage(__pfn_to_phys(_pfn)))
+
+#define dnode_to_nid(_dnode)						\
+	((_dnode) - dmem_pool.nodes)
+#define nid_to_dnode(nid)						\
+	(&dmem_pool.nodes[nid])
+
 #define for_each_dmem_node(_dnode)					\
 	for (_dnode = dmem_pool.nodes;					\
 		_dnode < dmem_pool.nodes + ARRAY_SIZE(dmem_pool.nodes);	\
 		_dnode++)
 
+#define for_each_dmem_region(_dnode, _dregion)				\
+	list_for_each_entry(_dregion, &(_dnode)->regions, node)
+
+static inline int *dmem_nodelist(int nid)
+{
+	return nid_to_dnode(nid)->nodelist;
+}
+
 void __init dmem_init(void)
 {
 	struct dmem_node *dnode;
@@ -135,3 +162,649 @@ int dmem_region_register(int node, phys_addr_t start, phys_addr_t end)
 	return 0;
 }
 
+#define PENALTY_FOR_DMEM_SHARED_NODE		(1)
+
+static int dmem_nodeload[MAX_NUMNODES] __initdata;
+
+/* Evaluate penalty for each dmem node */
+static int __init dmem_evaluate_node(int local, int node)
+{
+	int penalty;
+
+	/* Use the distance array to find the distance */
+	penalty = node_distance(local, node);
+
+	/* Penalize nodes under us ("prefer the next node") */
+	penalty += (node < local);
+
+	/* Give preference to headless and unused nodes */
+	if (!cpumask_empty(cpumask_of_node(node)))
+		penalty += PENALTY_FOR_NODE_WITH_CPUS;
+
+	/* Penalize dmem-node shared with kernel */
+	if (node_state(node, N_MEMORY))
+		penalty += PENALTY_FOR_DMEM_SHARED_NODE;
+
+	/* Slight preference for less loaded node */
+	penalty *= (nr_online_nodes * MAX_NUMNODES);
+
+	penalty += dmem_nodeload[node];
+
+	return penalty;
+}
+
+static int __init find_next_dmem_node(int local, nodemask_t *used_nodes)
+{
+	struct dmem_node *dnode;
+	int node, best_node = NUMA_NO_NODE;
+	int penalty, min_penalty = INT_MAX;
+
+	/* Invalid node is not suitable to call node_distance */
+	if (!node_state(local, N_POSSIBLE))
+		return NUMA_NO_NODE;
+
+	/* Use the local node if we haven't already */
+	if (!node_isset(local, *used_nodes)) {
+		node_set(local, *used_nodes);
+		return local;
+	}
+
+	for_each_dmem_node(dnode) {
+		if (list_empty(&dnode->regions))
+			continue;
+
+		node = dnode_to_nid(dnode);
+
+		/* Don't want a node to appear more than once */
+		if (node_isset(node, *used_nodes))
+			continue;
+
+		penalty = dmem_evaluate_node(local, node);
+
+		if (penalty < min_penalty) {
+			min_penalty = penalty;
+			best_node = node;
+		}
+	}
+
+	if (best_node >= 0)
+		node_set(best_node, *used_nodes);
+
+	return best_node;
+}
+
+static int __init dmem_node_init(struct dmem_node *dnode)
+{
+	int *nodelist;
+	nodemask_t used_nodes;
+	int local, node, prev;
+	int load;
+	int i = 0;
+
+	nodelist = dnode->nodelist;
+	nodes_clear(used_nodes);
+	local = dnode_to_nid(dnode);
+	prev = local;
+	load = nr_online_nodes;
+
+	while ((node = find_next_dmem_node(local, &used_nodes)) >= 0) {
+		/*
+		 * We don't want to pressure a particular node.
+		 * So adding penalty to the first node in same
+		 * distance group to make it round-robin.
+		 */
+		if (node_distance(local, node) != node_distance(local, prev))
+			dmem_nodeload[node] = load;
+
+		nodelist[i++] = prev = node;
+		load--;
+	}
+
+	return 0;
+}
+
+static void __init dmem_region_uinit(struct dmem_region *dregion)
+{
+	unsigned long nr_pages, size, *bitmap = dregion->error_bitmap;
+
+	if (!bitmap)
+		return;
+
+	nr_pages = __phys_to_pfn(dregion->reserved_end_addr)
+		- __phys_to_pfn(dregion->reserved_start_addr);
+
+	WARN_ON(!nr_pages);
+
+	size = BITS_TO_LONGS(nr_pages) * sizeof(long);
+	if (size > sizeof(dregion->static_bitmap))
+		kfree(bitmap);
+	dregion->error_bitmap = NULL;
+}
+
+/*
+ * we only stop allocator to use the reserved page and do not
+ * reture pages back if anything goes wrong
+ */
+static void __init dmem_uinit(void)
+{
+	struct dmem_region *dregion, *dr;
+	struct dmem_node *dnode;
+
+	for_each_dmem_node(dnode) {
+		dnode->nodelist[0] = NUMA_NO_NODE;
+		list_for_each_entry_safe(dregion, dr, &dnode->regions, node) {
+			dmem_region_uinit(dregion);
+			dregion->reserved_start_addr =
+				dregion->reserved_end_addr = 0;
+			list_del(&dregion->node);
+		}
+	}
+
+	dmem_pool.region_num = 0;
+	dmem_pool.registered_pages = 0;
+}
+
+static int __init dmem_region_init(struct dmem_region *dregion)
+{
+	unsigned long *bitmap, size, nr_pages;
+
+	nr_pages = __phys_to_pfn(dregion->reserved_end_addr)
+		- __phys_to_pfn(dregion->reserved_start_addr);
+
+	size = BITS_TO_LONGS(nr_pages) * sizeof(long);
+	if (size <= sizeof(dregion->static_error_bitmap)) {
+		bitmap = &dregion->static_error_bitmap;
+	} else {
+		bitmap = kzalloc(size, GFP_KERNEL);
+		if (!bitmap)
+			return -ENOMEM;
+	}
+	dregion->error_bitmap = bitmap;
+	return 0;
+}
+
+/*
+ * dmem memory is not 'struct page' backend, i.e, the kernel threats
+ * it as invalid pfn
+ */
+static int __init dmem_check_region(struct dmem_region *dregion)
+{
+	unsigned long pfn;
+
+	for (pfn = __phys_to_pfn(dregion->reserved_start_addr);
+	      pfn < __phys_to_pfn(dregion->reserved_end_addr); pfn++) {
+		if (!WARN_ON(pfn_valid(pfn)))
+			continue;
+
+		pr_err("dmem: check pfn %#lx failed, its memory was not properly reserved\n",
+			pfn);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int __init dmem_late_init(void)
+{
+	struct dmem_region *dregion;
+	struct dmem_node *dnode;
+	int ret;
+
+	for_each_dmem_node(dnode) {
+		dmem_node_init(dnode);
+
+		for_each_dmem_region(dnode, dregion) {
+			ret = dmem_region_init(dregion);
+			if (ret)
+				goto exit;
+			ret = dmem_check_region(dregion);
+			if (ret)
+				goto exit;
+		}
+	}
+	return ret;
+exit:
+	dmem_uinit();
+	return ret;
+}
+late_initcall(dmem_late_init);
+
+static int dmem_alloc_region_init(struct dmem_region *dregion,
+				  unsigned long *dpages)
+{
+	unsigned long start, end, *bitmap, size;
+
+	start = DMEM_PAGE_UP(dregion->reserved_start_addr);
+	end = DMEM_PAGE_DOWN(dregion->reserved_end_addr);
+
+	*dpages = end - start;
+	if (!*dpages)
+		return 0;
+
+	size = BITS_TO_LONGS(*dpages) * sizeof(long);
+	if (size <= sizeof(dregion->static_bitmap))
+		bitmap = &dregion->static_bitmap;
+	else {
+		bitmap = kzalloc(size, GFP_KERNEL);
+		if (!bitmap)
+			return -ENOMEM;
+	}
+
+	dregion->bitmap = bitmap;
+	dregion->next_free_pos = 0;
+	dregion->dpage_start_pfn = start;
+	dregion->dpage_end_pfn = end;
+
+	dmem_pool.unaligned_pages += __phys_to_pfn((dpage_to_phys(start)
+		- dregion->reserved_start_addr));
+	dmem_pool.unaligned_pages += __phys_to_pfn(dregion->reserved_end_addr
+		- dpage_to_phys(end));
+	return 0;
+}
+
+static bool dmem_dpage_is_error(struct dmem_region *dregion, phys_addr_t dpage)
+{
+	unsigned long valid_pages;
+	unsigned long pos_pfn, pos_offset;
+	unsigned long pages_per_dpage = DMEM_PAGE_SIZE >> PAGE_SHIFT;
+	phys_addr_t reserved_start_pfn;
+
+	reserved_start_pfn = __phys_to_pfn(dregion->reserved_start_addr);
+	valid_pages = dpage_to_pfn(dregion->dpage_end_pfn) - reserved_start_pfn;
+
+	pos_offset = dpage_to_pfn(dpage) - reserved_start_pfn;
+	pos_pfn = find_next_bit(dregion->error_bitmap, valid_pages, pos_offset);
+	if (pos_pfn < pos_offset + pages_per_dpage)
+		return true;
+	return false;
+}
+
+static unsigned long
+dmem_alloc_bitmap_clear(struct dmem_region *dregion, phys_addr_t dpage,
+			unsigned int dpages_nr)
+{
+	u64 pos = dpage - dregion->dpage_start_pfn;
+	unsigned int i;
+	unsigned long err_num = 0;
+
+	for (i = 0; i < dpages_nr; i++) {
+		if (dmem_dpage_is_error(dregion, dpage + i)) {
+			WARN_ON(!test_bit(pos + i, dregion->bitmap));
+			err_num++;
+		} else {
+			WARN_ON(!__test_and_clear_bit(pos + i,
+						      dregion->bitmap));
+		}
+	}
+	return err_num;
+}
+
+/* set or clear corresponding bit on allocation bitmap based on error bitmap */
+static unsigned long dregion_alloc_bitmap_set_clear(struct dmem_region *dregion,
+						    bool set)
+{
+	unsigned long pos_pfn, pos_offset;
+	unsigned long valid_pages, mce_dpages = 0;
+	phys_addr_t dpage, reserved_start_pfn;
+
+	reserved_start_pfn = __phys_to_pfn(dregion->reserved_start_addr);
+
+	valid_pages = dpage_to_pfn(dregion->dpage_end_pfn) - reserved_start_pfn;
+	pos_offset = dpage_to_pfn(dregion->dpage_start_pfn)
+		- reserved_start_pfn;
+try_set:
+	pos_pfn = find_next_bit(dregion->error_bitmap, valid_pages, pos_offset);
+
+	if (pos_pfn >= valid_pages)
+		return mce_dpages;
+	mce_dpages++;
+	dpage = pfn_to_dpage(pos_pfn + reserved_start_pfn);
+	if (set)
+		WARN_ON(__test_and_set_bit(dpage - dregion->dpage_start_pfn,
+					   dregion->bitmap));
+	else
+		WARN_ON(!__test_and_clear_bit(dpage - dregion->dpage_start_pfn,
+					      dregion->bitmap));
+	pos_offset = dpage_to_pfn(dpage + 1) - reserved_start_pfn;
+	goto try_set;
+}
+
+static void dmem_uinit_check_alloc_bitmap(struct dmem_region *dregion)
+{
+	unsigned long dpages, size;
+
+	dregion_alloc_bitmap_set_clear(dregion, false);
+
+	dpages = dregion->dpage_end_pfn - dregion->dpage_start_pfn;
+	size = BITS_TO_LONGS(dpages) * sizeof(long);
+	WARN_ON(!bitmap_empty(dregion->bitmap, size * BITS_PER_BYTE));
+}
+
+static void dmem_alloc_region_uinit(struct dmem_region *dregion)
+{
+	unsigned long dpages, size, *bitmap = dregion->bitmap;
+
+	if (!bitmap)
+		return;
+
+	dpages = dregion->dpage_end_pfn - dregion->dpage_start_pfn;
+	WARN_ON(!dpages);
+
+	dmem_uinit_check_alloc_bitmap(dregion);
+
+	size = BITS_TO_LONGS(dpages) * sizeof(long);
+	if (size > sizeof(dregion->static_bitmap))
+		kfree(bitmap);
+	dregion->bitmap = NULL;
+}
+
+static void __dmem_alloc_uinit(void)
+{
+	struct dmem_node *dnode;
+	struct dmem_region *dregion;
+
+	if (!dmem_pool.dpage_shift)
+		return;
+
+	dmem_pool.unaligned_pages = 0;
+
+	for_each_dmem_node(dnode) {
+		for_each_dmem_region(dnode, dregion)
+			dmem_alloc_region_uinit(dregion);
+
+		dnode->total_dpages = dnode->free_dpages = 0;
+	}
+
+	dmem_pool.dpage_shift = 0;
+	dmem_pool.total_dpages = dmem_pool.free_dpages = 0;
+}
+
+static void dnode_count_free_dpages(struct dmem_node *dnode, long dpages)
+{
+	dnode->free_dpages += dpages;
+	dmem_pool.free_dpages += dpages;
+}
+
+/*
+ * uninitialize dmem allocator
+ *
+ * all dpages should be freed before calling it
+ */
+void dmem_alloc_uinit(void)
+{
+	mutex_lock(&dmem_pool.lock);
+	if (!--dmem_pool.user_count)
+		__dmem_alloc_uinit();
+	mutex_unlock(&dmem_pool.lock);
+}
+EXPORT_SYMBOL(dmem_alloc_uinit);
+
+/*
+ * initialize dmem allocator
+ *   @dpage_shift: the shift bits of dmem page size used to manange
+ *      dmem memory, it should be CPU's nature page size at least
+ *
+ * Note: the page size the allocator used isn't the same thing with
+ *       the alignment used to reserve dmem memory
+ */
+int dmem_alloc_init(unsigned long dpage_shift)
+{
+	struct dmem_node *dnode;
+	struct dmem_region *dregion;
+	unsigned long dpages;
+	int ret = 0;
+
+	if (dpage_shift < PAGE_SHIFT)
+		return -EINVAL;
+
+	mutex_lock(&dmem_pool.lock);
+
+	if (dmem_pool.dpage_shift) {
+		/*
+		 * double init on the same page size is okay
+		 * to make the unit tests happy
+		 */
+		if (dmem_pool.dpage_shift != dpage_shift)
+			ret = -EBUSY;
+
+		goto exit;
+	}
+
+	dmem_pool.dpage_shift = dpage_shift;
+
+	for_each_dmem_node(dnode) {
+		for_each_dmem_region(dnode, dregion) {
+			ret = dmem_alloc_region_init(dregion, &dpages);
+			if (ret < 0) {
+				__dmem_alloc_uinit();
+				goto exit;
+			}
+
+			dnode_count_free_dpages(dnode, dpages);
+		}
+		dnode->total_dpages = dnode->free_dpages;
+	}
+
+	dmem_pool.total_dpages = dmem_pool.free_dpages;
+
+	if (dmem_pool.unaligned_pages && !ret)
+		pr_warn("dmem: %llu pages are wasted due to alignment\n",
+			(unsigned long long)dmem_pool.unaligned_pages);
+exit:
+	if (!ret)
+		dmem_pool.user_count++;
+
+	mutex_unlock(&dmem_pool.lock);
+	return ret;
+}
+EXPORT_SYMBOL(dmem_alloc_init);
+
+static phys_addr_t
+dmem_alloc_region_page(struct dmem_region *dregion, unsigned int try_max,
+		       unsigned int *result_nr)
+{
+	unsigned long pos, dpages;
+	unsigned int i;
+
+	/* no dpage is available in this region */
+	if (!dregion->bitmap)
+		return 0;
+
+	dpages = dregion->dpage_end_pfn - dregion->dpage_start_pfn;
+
+	/* no free page in this region */
+	if (dregion->next_free_pos >= dpages)
+		return 0;
+
+	pos = find_next_zero_bit(dregion->bitmap, dpages,
+				 dregion->next_free_pos);
+	if (pos >= dpages) {
+		dregion->next_free_pos = pos;
+		return 0;
+	}
+
+	__set_bit(pos, dregion->bitmap);
+
+	/* do not go beyond the region */
+	try_max = min(try_max, (unsigned int)(dpages - pos - 1));
+	for (i = 1; i < try_max; i++)
+		if (__test_and_set_bit(pos + i, dregion->bitmap))
+			break;
+
+	*result_nr = i;
+	dregion->next_free_pos = pos + *result_nr;
+	return dpage_to_phys(dregion->dpage_start_pfn + pos);
+}
+
+/*
+ * allocate dmem pages from the nodelist
+ *
+ *   @nodelist: dmem_node's nodelist
+ *   @nodemask: nodemask for filtering the dmem nodelist
+ *   @try_max: try to allocate @try_max dpages if possible
+ *   @result_nr: allocated dpage number returned to the caller
+ *
+ * return the physical address of the first dpage allocated from dmem
+ * pool, or 0 on failure. The allocated dpage number is filled into
+ * @result_nr
+ */
+static phys_addr_t
+dmem_alloc_pages_from_nodelist(int *nodelist, nodemask_t *nodemask,
+			       unsigned int try_max, unsigned int *result_nr)
+{
+	struct dmem_node *dnode;
+	struct dmem_region *dregion;
+	phys_addr_t addr = 0;
+	int node, i;
+	unsigned int local_result_nr;
+
+	WARN_ON(try_max > 1 && !result_nr);
+
+	if (!result_nr)
+		result_nr = &local_result_nr;
+
+	*result_nr = 0;
+
+	for (i = 0; !addr && i < ARRAY_SIZE(dnode->nodelist); i++) {
+		node = nodelist[i];
+
+		if (nodemask && !node_isset(node, *nodemask))
+			continue;
+
+		mutex_lock(&dmem_pool.lock);
+
+		WARN_ON(!dmem_pool.dpage_shift);
+
+		dnode = &dmem_pool.nodes[node];
+		for_each_dmem_region(dnode, dregion) {
+			addr = dmem_alloc_region_page(dregion, try_max,
+						      result_nr);
+			if (addr) {
+				dnode_count_free_dpages(dnode,
+							-(long)(*result_nr));
+				break;
+			}
+		}
+
+		mutex_unlock(&dmem_pool.lock);
+	}
+	return addr;
+}
+
+/*
+ * allocate a dmem page from the dmem pool and try to allocate more
+ * continuous dpages if @try_max is not less than 1
+ *
+ *   @nid: the NUMA node the dmem page got from
+ *   @nodemask: nodemask for filtering the dmem nodelist
+ *   @try_max: try to allocate @try_max dpages if possible
+ *   @result_nr: allocated dpage number returned to the caller
+ *
+ * return the physical address of the first dpage allocated from dmem
+ * pool, or 0 on failure. The allocated dpage number is filled into
+ * @result_nr
+ */
+phys_addr_t
+dmem_alloc_pages_nodemask(int nid, nodemask_t *nodemask, unsigned int try_max,
+			  unsigned int *result_nr)
+{
+	int *nodelist;
+
+	if (nid >= sizeof(ARRAY_SIZE(dmem_pool.nodes)))
+		return 0;
+
+	nodelist = dmem_nodelist(nid);
+	return dmem_alloc_pages_from_nodelist(nodelist, nodemask,
+					      try_max, result_nr);
+}
+EXPORT_SYMBOL(dmem_alloc_pages_nodemask);
+
+/*
+ * dmem_alloc_pages_vma - Allocate pages for a VMA.
+ *
+ *   @vma:  Pointer to VMA or NULL if not available.
+ *   @addr: Virtual Address of the allocation. Must be inside the VMA.
+ *   @try_max: try to allocate @try_max dpages if possible
+ *   @result_nr: allocated dpage number returned to the caller
+ *
+ * Return the physical address of the first dpage allocated from dmem
+ * pool, or 0 on failure. The allocated dpage number is filled into
+ * @result_nr
+ */
+phys_addr_t
+dmem_alloc_pages_vma(struct vm_area_struct *vma, unsigned long addr,
+		     unsigned int try_max, unsigned int *result_nr)
+{
+	phys_addr_t phys_addr;
+	int *nl;
+	unsigned int cpuset_mems_cookie;
+
+retry_cpuset:
+	nl = dmem_nodelist(numa_node_id());
+
+	phys_addr = dmem_alloc_pages_from_nodelist(nl, NULL, try_max,
+						   result_nr);
+	if (unlikely(!phys_addr && read_mems_allowed_retry(cpuset_mems_cookie)))
+		goto retry_cpuset;
+
+	return phys_addr;
+}
+EXPORT_SYMBOL(dmem_alloc_pages_vma);
+
+/*
+ * Don't need to call it in a lock.
+ * This function uses the reserved addresses those are initially registered
+ * and will not be modified at run time.
+ */
+static struct dmem_region *find_dmem_region(phys_addr_t phys_addr,
+					    struct dmem_node **pdnode)
+{
+	struct dmem_node *dnode;
+	struct dmem_region *dregion;
+
+	for_each_dmem_node(dnode)
+		for_each_dmem_region(dnode, dregion) {
+			if (dregion->reserved_start_addr > phys_addr)
+				continue;
+			if (dregion->reserved_end_addr <= phys_addr)
+				continue;
+
+			*pdnode = dnode;
+			return dregion;
+		}
+
+	return NULL;
+}
+
+/*
+ * free dmem page to the dmem pool
+ *   @addr: the physical addree will be freed
+ *   @dpage_nr: the number of dpage to be freed
+ */
+void dmem_free_pages(phys_addr_t addr, unsigned int dpages_nr)
+{
+	struct dmem_region *dregion;
+	struct dmem_node *pdnode = NULL;
+	phys_addr_t dpage = phys_to_dpage(addr);
+	u64 pos;
+	unsigned long err_dpages;
+
+	mutex_lock(&dmem_pool.lock);
+
+	WARN_ON(!dmem_pool.dpage_shift);
+
+	dregion = find_dmem_region(addr, &pdnode);
+	WARN_ON(!dregion || !dregion->bitmap || !pdnode);
+
+	pos = dpage - dregion->dpage_start_pfn;
+	dregion->next_free_pos = min(dregion->next_free_pos, pos);
+
+	/* it is not possible to span multiple regions */
+	WARN_ON(dpage + dpages_nr - 1 >= dregion->dpage_end_pfn);
+
+	err_dpages = dmem_alloc_bitmap_clear(dregion, dpage, dpages_nr);
+
+	dnode_count_free_dpages(pdnode, dpages_nr - err_dpages);
+	mutex_unlock(&dmem_pool.lock);
+}
+EXPORT_SYMBOL(dmem_free_pages);
-- 
2.28.0

