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(). Additional flags might be added later. 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 2ed36c8562ac..a498a7368cff 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -343,6 +343,15 @@ struct mem_cgroup { extern struct mem_cgroup *root_mem_cgroup; +enum page_memcg_flags { + /* page->memcg_data is a pointer to an objcgs vector */ + PG_MEMCG_OBJ_CGROUPS, + /* the next bit after the last actual flag */ + PG_MEMCG_LAST_FLAG, +}; + +#define MEMCG_FLAGS_MASK ((1UL << PG_MEMCG_LAST_FLAG) - 1) + /* * page_mem_cgroup - get the memory cgroup associated with a page * @page: a pointer to the page struct @@ -371,13 +380,7 @@ 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; @@ -422,7 +425,12 @@ static inline void clear_page_mem_cgroup(struct page *page) */ 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); + + return (struct obj_cgroup **)(memcg_data & ~MEMCG_FLAGS_MASK); } /* @@ -437,8 +445,8 @@ 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)) - return (struct obj_cgroup **)(memcg_data & ~0x1UL); + if (memcg_data && test_bit(PG_MEMCG_OBJ_CGROUPS, &memcg_data)) + return (struct obj_cgroup **)(memcg_data & ~MEMCG_FLAGS_MASK); return NULL; } @@ -453,7 +461,11 @@ 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); } /* -- 2.26.2
