[PATCH v3] resource: Merge resources on a node when hot-adding memory

[Rashmica Gupta]

When hot-removing memory release_mem_region_adjustable() splits
iomem resources if they are not the exact size of the memory being
hot-deleted. Adding this memory back to the kernel adds a new
resource.

Eg a node has memory 0x0 - 0xfffffffff. Offlining and hot-removing
1GB from 0xf40000000 results in the single resource 0x0-0xfffffffff being
split into two resources: 0x0-0xf3fffffff and 0xf80000000-0xfffffffff.

When we hot-add the memory back we now have three resources:
0x0-0xf3fffffff, 0xf40000000-0xf7fffffff, and 0xf80000000-0xfffffffff.

Now if we try to remove some memory that overlaps these resources,
like 2GB from 0xf40000000, release_mem_region_adjustable() fails as it
expects the chunk of memory to be within the boundaries of a single
resource.

This patch adds a function request_resource_and_merge(). This is called
instead of request_resource_conflict() when registering a resource in
add_memory(). It calls request_resource_conflict() and if hot-removing is
enabled (if it isn't we won't get resource fragmentation) we attempt to
merge contiguous resources on the node.

Signed-off-by: Rashmica Gupta <rashmica.g@xxxxxxxxx>
---
v2->v3: Update Xen balloon, make the commit msg and a comment clearer,
and changed '>' to '>=' when comparing the end of a resource and the
end of a node.

v1->v2: Only attempt to merge resources if hot-remove is enabled.

 drivers/xen/balloon.c          |   3 +-
 include/linux/ioport.h         |   2 +
 include/linux/memory_hotplug.h |   2 +-
 kernel/resource.c              | 120 +++++++++++++++++++++++++++++++++++++++++
 mm/memory_hotplug.c            |  22 ++++----
 5 files changed, 136 insertions(+), 13 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 065f0b607373..9b972b37b0da 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -401,7 +401,8 @@ static enum bp_state reserve_additional_memory(void)
 	 * callers drop the mutex before trying again.
 	 */
 	mutex_unlock(&balloon_mutex);
-	rc = add_memory_resource(nid, resource, memhp_auto_online);
+	rc = add_memory_resource(nid, resource->start, resource_size(resource),
+				 memhp_auto_online);
 	mutex_lock(&balloon_mutex);
 
 	if (rc) {
diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index da0ebaec25f0..f5b93a711e86 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -189,6 +189,8 @@ extern int allocate_resource(struct resource *root, struct resource *new,
 						       resource_size_t,
 						       resource_size_t),
 			     void *alignf_data);
+extern struct resource *request_resource_and_merge(struct resource *parent,
+						   struct resource *new, int nid);
 struct resource *lookup_resource(struct resource *root, resource_size_t start);
 int adjust_resource(struct resource *res, resource_size_t start,
 		    resource_size_t size);
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 4e9828cda7a2..9c00f97c8cc6 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -322,7 +322,7 @@ static inline void remove_memory(int nid, u64 start, u64 size) {}
 extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
 		void *arg, int (*func)(struct memory_block *, void *));
 extern int add_memory(int nid, u64 start, u64 size);
-extern int add_memory_resource(int nid, struct resource *resource, bool online);
+extern int add_memory_resource(int nid, u64 start, u64 size, bool online);
 extern int arch_add_memory(int nid, u64 start, u64 size,
 		struct vmem_altmap *altmap, bool want_memblock);
 extern void move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn,
diff --git a/kernel/resource.c b/kernel/resource.c
index 30e1bc68503b..a31d3f5bccb7 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1621,3 +1621,123 @@ static int __init strict_iomem(char *str)
 }
 
 __setup("iomem=", strict_iomem);
+
+#ifdef CONFIG_MEMORY_HOTPLUG
+#ifdef CONFIG_MEMORY_HOTREMOVE
+/*
+ * Attempt to merge resource and it's sibling
+ */
+static int merge_resources(struct resource *res)
+{
+	struct resource *next;
+	struct resource *tmp;
+	uint64_t size;
+	int ret = -EINVAL;
+
+	next = res->sibling;
+
+	/*
+	 * Not sure how to handle two different children. So only attempt
+	 * to merge two resources if neither have children, only one has a
+	 * child or if both have the same child.
+	 */
+	if ((res->child && next->child) && (res->child != next->child))
+		return ret;
+
+	if (res->end + 1 != next->start)
+		return ret;
+
+	if (res->flags != next->flags)
+		return ret;
+
+	/* Update sibling and child of resource */
+	res->sibling = next->sibling;
+	tmp = res->child;
+	if (!res->child)
+		res->child = next->child;
+
+	size = next->end - res->start + 1;
+	ret = __adjust_resource(res, res->start, size);
+	if (ret) {
+		/* Failed so restore resource to original state */
+		res->sibling = next;
+		res->child = tmp;
+		return ret;
+	}
+
+	free_resource(next);
+
+	return ret;
+}
+
+/*
+ * Attempt to merge resources on the node
+ */
+static void merge_node_resources(int nid, struct resource *parent)
+{
+	struct resource *res;
+	uint64_t start_addr;
+	uint64_t end_addr;
+	int ret;
+
+	start_addr = node_start_pfn(nid) << PAGE_SHIFT;
+	end_addr = node_end_pfn(nid) << PAGE_SHIFT;
+
+	write_lock(&resource_lock);
+
+	/* Get the first resource */
+	res = parent->child;
+
+	while (res) {
+		/* Check that the resource is within the node */
+		if (res->start < start_addr) {
+			res = res->sibling;
+			continue;
+		}
+		/* Exit if sibling resource is past end of node */
+		if (res->sibling->end >= end_addr)
+			break;
+
+		ret = merge_resources(res);
+		if (!ret)
+			continue;
+		res = res->sibling;
+	}
+	write_unlock(&resource_lock);
+}
+#endif /* CONFIG_MEMORY_HOTREMOVE */
+
+/**
+ * request_resource_and_merge() - request an I/O or memory resource for hot-add
+ * @parent: parent resource descriptor
+ * @new: resource descriptor desired by caller
+ * @nid: node id of the node we want the resource on
+ *
+ * If no conflict resource then attempt to merge resources on the node.
+ *
+ * This is intended to cleanup the fragmentation of resources that occurs when
+ * hot-removing memory (see release_mem_region_adjustable). If hot-removing is
+ * not enabled then there is no point trying to merge resources.
+ *
+ * Note that the inability to merge resources is not an error.
+ *
+ * Return: NULL for successful request of resource and conflict resource if
+ * there was a conflict.
+ */
+struct resource *request_resource_and_merge(struct resource *parent,
+					    struct resource *new, int nid)
+{
+	struct resource *conflict;
+
+	conflict = request_resource_conflict(parent, new);
+
+	if (conflict)
+		return conflict;
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+	merge_node_resources(nid, parent);
+#endif /* CONFIG_MEMORY_HOTREMOVE */
+
+	return NULL;
+}
+#endif /* CONFIG_MEMORY_HOTPLUG */
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 7deb49f69e27..2e342f5ce322 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -97,7 +97,7 @@ void mem_hotplug_done(void)
 }
 
 /* add this memory to iomem resource */
-static struct resource *register_memory_resource(u64 start, u64 size)
+static struct resource *register_memory_resource(int nid, u64 start, u64 size)
 {
 	struct resource *res, *conflict;
 	res = kzalloc(sizeof(struct resource), GFP_KERNEL);
@@ -108,7 +108,7 @@ static struct resource *register_memory_resource(u64 start, u64 size)
 	res->start = start;
 	res->end = start + size - 1;
 	res->flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
-	conflict =  request_resource_conflict(&iomem_resource, res);
+	conflict =  request_resource_and_merge(&iomem_resource, res, nid);
 	if (conflict) {
 		if (conflict->desc == IORES_DESC_DEVICE_PRIVATE_MEMORY) {
 			pr_debug("Device unaddressable memory block "
@@ -122,11 +122,15 @@ static struct resource *register_memory_resource(u64 start, u64 size)
 	return res;
 }
 
-static void release_memory_resource(struct resource *res)
+static void release_memory_resource(struct resource *res, u64 start, u64 size)
 {
 	if (!res)
 		return;
+#ifdef CONFIG_MEMORY_HOTREMOVE
+	release_mem_region_adjustable(&iomem_resource, start, size);
+#else
 	release_resource(res);
+#endif
 	kfree(res);
 	return;
 }
@@ -1096,17 +1100,13 @@ static int online_memory_block(struct memory_block *mem, void *arg)
 }
 
 /* we are OK calling __meminit stuff here - we have CONFIG_MEMORY_HOTPLUG */
-int __ref add_memory_resource(int nid, struct resource *res, bool online)
+int __ref add_memory_resource(int nid, u64 start, u64 size, bool online)
 {
-	u64 start, size;
 	pg_data_t *pgdat = NULL;
 	bool new_pgdat;
 	bool new_node;
 	int ret;
 
-	start = res->start;
-	size = resource_size(res);
-
 	ret = check_hotplug_memory_range(start, size);
 	if (ret)
 		return ret;
@@ -1195,13 +1195,13 @@ int __ref add_memory(int nid, u64 start, u64 size)
 	struct resource *res;
 	int ret;
 
-	res = register_memory_resource(start, size);
+	res = register_memory_resource(nid, start, size);
 	if (IS_ERR(res))
 		return PTR_ERR(res);
 
-	ret = add_memory_resource(nid, res, memhp_auto_online);
+	ret = add_memory_resource(nid, start, size, memhp_auto_online);
 	if (ret < 0)
-		release_memory_resource(res);
+		release_memory_resource(res, start, size);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(add_memory);
-- 
2.14.4