The lowest bit in page->memcg_data is used to distinguish between
struct memory_cgroup pointer and a pointer to a objcgs array.
All checks and modifications of this bit are open-coded.
Let's formalize it using page memcg flags, defined in page_memcg_flags
enum and replace all open-coded accesses with test_bit()/__set_bit().
Few additional flags might be added later. Flags are intended to be
mutually exclusive.
Signed-off-by: Roman Gushchin <guro@xxxxxx>
---
include/linux/memcontrol.h | 34 +++++++++++++++++++++++-----------
1 file changed, 23 insertions(+), 11 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 48d4c2c1ce81..7ab5f92bb686 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -340,23 +340,25 @@ struct mem_cgroup {
extern struct mem_cgroup *root_mem_cgroup;
+enum page_memcg_flags {
+ /* page->memcg_data is a pointer to a objcgs vector */
+ PG_MEMCG_OBJ_CGROUPS,
+};
+
static inline struct mem_cgroup *page_mem_cgroup(struct page *page)
{
+ unsigned long memcg_data = page->memcg_data;
+
VM_BUG_ON_PAGE(PageSlab(page), page);
- return (struct mem_cgroup *)page->memcg_data;
+
+ return (struct mem_cgroup *)memcg_data;
}
static inline struct mem_cgroup *page_mem_cgroup_check(struct page *page)
{
unsigned long memcg_data = page->memcg_data;
- /*
- * The lowest bit set means that memcg isn't a valid
- * memcg pointer, but a obj_cgroups pointer.
- * In this case the page is shared and doesn't belong
- * to any specific memory cgroup.
- */
- if (memcg_data & 0x1UL)
+ if (test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data))
return NULL;
return (struct mem_cgroup *)memcg_data;
@@ -378,14 +380,20 @@ static inline void clear_page_mem_cgroup(struct page *page)
#ifdef CONFIG_MEMCG_KMEM
static inline struct obj_cgroup **page_obj_cgroups(struct page *page)
{
- return (struct obj_cgroup **)(page->memcg_data & ~0x1UL);
+ unsigned long memcg_data = page->memcg_data;
+
+ VM_BUG_ON_PAGE(memcg_data && !test_bit(PG_MEMCG_OBJ_CGROUPS,
+ &memcg_data), page);
+ __clear_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data);
+
+ return (struct obj_cgroup **)memcg_data;
}
static inline struct obj_cgroup **page_obj_cgroups_check(struct page *page)
{
unsigned long memcg_data = page->memcg_data;
- if (memcg_data && (memcg_data & 0x1UL))
+ if (memcg_data && test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data))
return (struct obj_cgroup **)memcg_data;
return NULL;
@@ -394,7 +402,11 @@ static inline struct obj_cgroup **page_obj_cgroups_check(struct page *page)
static inline bool set_page_obj_cgroups(struct page *page,
struct obj_cgroup **objcgs)
{
- return !cmpxchg(&page->memcg_data, 0, (unsigned long)objcgs | 0x1UL);
+ unsigned long memcg_data = (unsigned long)objcgs;
+
+ __set_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data);
+
+ return !cmpxchg(&page->memcg_data, 0, memcg_data);
}
static inline void clear_page_obj_cgroups(struct page *page)
--
2.26.2
