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 <[email protected]> --- 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
