[PATCH v2 5/6] memcg: introduce swap_cgroup_init()/swap_cgroup_free()

[Jeff Liu <jeff.liu@oracle.com>]

Introduce swap_cgroup_init()/swap_cgroup_free() to allocate buffers when creating the first
non-root memcg and deallocate buffers on the last non-root memcg is gone.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
CC: Glauber Costa <glommer@parallels.com>
CC: Michal Hocko <mhocko@suse.cz>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
CC: Johannes Weiner <hannes@cmpxchg.org>
CC: Mel Gorman <mgorman@suse.de>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Sha Zhengju <handai.szj@taobao.com>

---
 include/linux/page_cgroup.h |   12 +++++
 mm/page_cgroup.c            |  108 +++++++++++++++++++++++++++++++++++++++----
 2 files changed, 110 insertions(+), 10 deletions(-)

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 777a524..1255cc9 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -113,6 +113,8 @@ extern unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id);
 extern unsigned short lookup_swap_cgroup_id(swp_entry_t ent);
 extern int swap_cgroup_swapon(int type, unsigned long max_pages);
 extern void swap_cgroup_swapoff(int type);
+extern int swap_cgroup_init(void);
+extern void swap_cgroup_free(void);
 #else
 
 static inline
@@ -138,6 +140,16 @@ static inline void swap_cgroup_swapoff(int type)
 	return;
 }
 
+static inline int swap_cgroup_init(void)
+{
+	return 0;
+}
+
+static inline void swap_cgroup_free(void)
+{
+	return;
+}
+
 #endif /* CONFIG_MEMCG_SWAP */
 
 #endif /* !__GENERATING_BOUNDS_H */
diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 189fbf5..0ebd127 100644
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -362,14 +362,28 @@ static int swap_cgroup_prepare(int type)
 	unsigned long idx, max;
 
 	ctrl = &swap_cgroup_ctrl[type];
+	if (!ctrl->length) {
+		/*
+		 * Bypass the buffer allocation if the corresponding swap
+		 * partition/file was turned off.
+		 */
+		pr_debug("couldn't allocate swap_cgroup on a disabled swap "
+			 "partition or file, index: %d\n", type);
+		return 0;
+	}
+
 	ctrl->map = vzalloc(ctrl->length * sizeof(void *));
-	if (!ctrl->map)
+	if (!ctrl->map) {
+		ctrl->length = 0;
 		goto nomem;
+	}
 
 	for (idx = 0; idx < ctrl->length; idx++) {
 		page = alloc_page(GFP_KERNEL | __GFP_ZERO);
-		if (!page)
+		if (!page) {
+			ctrl->length = 0;
 			goto not_enough_page;
+		}
 		ctrl->map[idx] = page;
 	}
 	return 0;
@@ -383,6 +397,32 @@ nomem:
 	return -ENOMEM;
 }
 
+/*
+ * free buffer for swap_cgroup.
+ */
+static void swap_cgroup_teardown(int type)
+{
+	struct page **map;
+	unsigned long length;
+	struct swap_cgroup_ctrl *ctrl;
+
+	ctrl = &swap_cgroup_ctrl[type];
+	map = ctrl->map;
+	length = ctrl->length;
+	ctrl->map = NULL;
+	ctrl->length = 0;
+
+	if (map) {
+		unsigned long i;
+		for (i = 0; i < length; i++) {
+			struct page *page = map[i];
+			if (page)
+				__free_page(page);
+		}
+		vfree(map);
+	}
+}
+
 static struct swap_cgroup *lookup_swap_cgroup(swp_entry_t ent,
 					struct swap_cgroup_ctrl **ctrlp)
 {
@@ -474,6 +514,56 @@ unsigned short lookup_swap_cgroup_id(swp_entry_t ent)
 	return sc ? sc->id : 0;
 }
 
+/*
+ * Allocate swap cgroup accounting structures when the first non-root
+ * memcg is created.
+ */
+int swap_cgroup_init(void)
+{
+	unsigned int type;
+
+	if (!do_swap_account)
+		return 0;
+
+	if (atomic_add_return(1, &memsw_accounting_users) != 1)
+		return 0;
+
+	mutex_lock(&swap_cgroup_mutex);
+	for (type = 0; type < nr_swapfiles; type++) {
+		if (swap_cgroup_prepare(type) < 0) {
+			mutex_unlock(&swap_cgroup_mutex);
+			goto nomem;
+		}
+	}
+	mutex_unlock(&swap_cgroup_mutex);
+	return 0;
+
+nomem:
+	pr_info("couldn't allocate enough memory for swap_cgroup "
+		"while creating non-root memcg.\n");
+	return -ENOMEM;
+}
+
+/*
+ * Deallocate swap cgroup accounting structures on the last non-root
+ * memcg removal.
+ */
+void swap_cgroup_free(void)
+{
+	unsigned int type;
+
+	if (!do_swap_account)
+		return;
+
+	if (atomic_sub_return(1, &memsw_accounting_users))
+		return;
+
+	mutex_lock(&swap_cgroup_mutex);
+	for (type = 0; type < nr_swapfiles; type++)
+		swap_cgroup_teardown(type);
+	mutex_unlock(&swap_cgroup_mutex);
+}
+
 int swap_cgroup_swapon(int type, unsigned long max_pages)
 {
 	unsigned long length;
@@ -482,20 +572,18 @@ int swap_cgroup_swapon(int type, unsigned long max_pages)
 	if (!do_swap_account)
 		return 0;
 
-	if (!atomic_read(&memsw_accounting_users))
-		return 0;
-
 	length = DIV_ROUND_UP(max_pages, SC_PER_PAGE);
 
 	ctrl = &swap_cgroup_ctrl[type];
 	mutex_lock(&swap_cgroup_mutex);
 	ctrl->length = length;
 	spin_lock_init(&ctrl->lock);
-	if (swap_cgroup_prepare(type)) {
-		/* memory shortage */
-		ctrl->length = 0;
-		mutex_unlock(&swap_cgroup_mutex);
-		goto nomem;
+	if (atomic_read(&memsw_accounting_users)) {
+		if (swap_cgroup_prepare(type)) {
+			/* memory shortage */
+			mutex_unlock(&swap_cgroup_mutex);
+			goto nomem;
+		}
 	}
 	mutex_unlock(&swap_cgroup_mutex);
 
-- 
1.7.9.5

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