[RFC PATCH 1/4] mm/resource: Move child to new resource when release mem region.

[lantianyu1986@gmail.com]

From: Tianyu Lan <Tianyu.Lan@microsoft.com>

When release mem region, old mem region may be splited to
two regions. Current allocate new struct resource for high
end mem region but not move child resources whose ranges are
in the high end range to new resource. When adjust old mem
region's range, adjust_resource() detects child region's range
is out of new range and return error. Move child resources to
high end resource before adjusting old mem range.

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
This patch is to prepare for memory hot-remove function
in Hyper-V balloon driver.
---
 kernel/resource.c | 38 ++++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 76036a41143b..1c7362825134 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -181,6 +181,38 @@ static struct resource *alloc_resource(gfp_t flags)
 	return res;
 }
 
+static void move_child_to_newresource(struct resource *old,
+				      struct resource *new)
+{
+	struct resource *tmp, **p, **np;
+
+	if (!old->child)
+		return;
+
+	p = &old->child;
+	np = &new->child;
+
+	for (;;) {
+		tmp = *p;
+		if (!tmp)
+			break;
+
+		if (tmp->start >= new->start && tmp->end <= new->end) {
+			tmp->parent = new;
+			*np = tmp;
+			np = &tmp->sibling;
+			*p = tmp->sibling;
+
+			if (!tmp->sibling)
+				*np = NULL;
+			continue;
+		}
+
+		p = &tmp->sibling;
+	}
+}
+
+
 /* Return the conflict entry if you can't request it */
 static struct resource * __request_resource(struct resource *root, struct resource *new)
 {
@@ -1246,9 +1278,6 @@ EXPORT_SYMBOL(__release_region);
  * Note:
  * - Additional release conditions, such as overlapping region, can be
  *   supported after they are confirmed as valid cases.
- * - When a busy memory resource gets split into two entries, the code
- *   assumes that all children remain in the lower address entry for
- *   simplicity.  Enhance this logic when necessary.
  */
 int release_mem_region_adjustable(struct resource *parent,
 				  resource_size_t start, resource_size_t size)
@@ -1331,11 +1360,12 @@ int release_mem_region_adjustable(struct resource *parent,
 			new_res->sibling = res->sibling;
 			new_res->child = NULL;
 
+			move_child_to_newresource(res, new_res);
+			res->sibling = new_res;
 			ret = __adjust_resource(res, res->start,
 						start - res->start);
 			if (ret)
 				break;
-			res->sibling = new_res;
 			new_res = NULL;
 		}
 
-- 
2.14.5