On Fri 02-10-20 10:25:59, Roman Gushchin wrote: > PageKmemcg flag is currently defined as a page type (like buddy, > offline, table and guard). Semantically it means that the page > was accounted as a kernel memory by the page allocator and has > to be uncharged on the release. > > As a side effect of defining the flag as a page type, the accounted > page can't be mapped to userspace (look at page_has_type() and > comments above). In particular, this blocks the accounting of > vmalloc-backed memory used by some bpf maps, because these maps > do map the memory to userspace. > > One option is to fix it by complicating the access to page->mapcount, > which provides some free bits for page->page_type. > > But it's way better to move this flag into page->memcg_data flags. > Indeed, the flag makes no sense without enabled memory cgroups > and memory cgroup pointer set in particular.
Completely agreed. Also this concept is already used for anon/ksm which set flags on the same pointer as the object. Having that outsourced to elsewhere is really harder to follow. > This commit replaces PageKmemcg() and __SetPageKmemcg() with > PageMemcgKmem() and an open-coded OR operation setting the memcg > pointer with the MEMCG_DATA_KMEM bit. __ClearPageKmemcg() can be > simple deleted, as the whole memcg_data is zeroed at once. > > As a bonus, on !CONFIG_MEMCG build the PageMemcgKmem() check will > be compiled out. > > Signed-off-by: Roman Gushchin <[email protected]> > Acked-by: Johannes Weiner <[email protected]> Acked-by: Michal Hocko <[email protected]> > --- > cover.txt | 4 ++-- > include/linux/memcontrol.h | 37 +++++++++++++++++++++++++++++++++---- > include/linux/page-flags.h | 11 ++--------- > mm/memcontrol.c | 16 +++++----------- > mm/page_alloc.c | 4 ++-- > 5 files changed, 44 insertions(+), 28 deletions(-) > > diff --git a/cover.txt b/cover.txt > index 32460cd3316e..cf23753cad15 100644 > --- a/cover.txt > +++ b/cover.txt > @@ -15,10 +15,10 @@ their memory can't be accounted because of this > implementation detail. > > This patchset removes this limitation by moving the PageKmemcg flag > into one of the free bits of the page->mem_cgroup pointer. Also it > -formalizes all accesses to the page->mem_cgroup and page->obj_cgroups > +formalizes accesses to the page->mem_cgroup and page->obj_cgroups > using new helpers, adds several checks and removes a couple of obsolete > functions. As the result the code became more robust with fewer > -open-coded bits tricks. > +open-coded bit tricks. > > v5: > - added ~MEMCG_DATA_FLAGS_MASK to page_memcg_rcu(), by Michal > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 99a4841d658b..7c9d43476166 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -346,8 +346,10 @@ extern struct mem_cgroup *root_mem_cgroup; > enum page_memcg_data_flags { > /* page->memcg_data is a pointer to an objcgs vector */ > MEMCG_DATA_OBJCGS = (1UL << 0), > + /* page has been accounted as a non-slab kernel page */ > + MEMCG_DATA_KMEM = (1UL << 1), > /* the next bit after the last actual flag */ > - __NR_MEMCG_DATA_FLAGS = (1UL << 1), > + __NR_MEMCG_DATA_FLAGS = (1UL << 2), > }; > > #define MEMCG_DATA_FLAGS_MASK (__NR_MEMCG_DATA_FLAGS - 1) > @@ -369,8 +371,12 @@ enum page_memcg_data_flags { > */ > static inline struct mem_cgroup *page_memcg(struct page *page) > { > + unsigned long memcg_data = page->memcg_data; > + > VM_BUG_ON_PAGE(PageSlab(page), page); > - return (struct mem_cgroup *)page->memcg_data; > + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_OBJCGS, page); > + > + return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > } > > /* > @@ -387,7 +393,8 @@ static inline struct mem_cgroup *page_memcg_rcu(struct > page *page) > VM_BUG_ON_PAGE(PageSlab(page), page); > WARN_ON_ONCE(!rcu_read_lock_held()); > > - return (struct mem_cgroup *)READ_ONCE(page->memcg_data); > + return (struct mem_cgroup *)(READ_ONCE(page->memcg_data) & > + ~MEMCG_DATA_FLAGS_MASK); > } > > /* > @@ -416,7 +423,21 @@ static inline struct mem_cgroup *page_memcg_check(struct > page *page) > if (memcg_data & MEMCG_DATA_OBJCGS) > return NULL; > > - return (struct mem_cgroup *)memcg_data; > + return (struct mem_cgroup *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > +} > + > +/* > + * PageMemcgKmem - check if the page has MemcgKmem flag set > + * @page: a pointer to the page struct > + * > + * Checks if the page has MemcgKmem flag set. The caller must ensure that > + * the page has an associated memory cgroup. It's not safe to call this > function > + * against some types of pages, e.g. slab pages. > + */ > +static inline bool PageMemcgKmem(struct page *page) > +{ > + VM_BUG_ON_PAGE(page->memcg_data & MEMCG_DATA_OBJCGS, page); > + return page->memcg_data & MEMCG_DATA_KMEM; > } > > #ifdef CONFIG_MEMCG_KMEM > @@ -435,6 +456,7 @@ static inline struct obj_cgroup **page_objcgs(struct page > *page) > unsigned long memcg_data = READ_ONCE(page->memcg_data); > > VM_BUG_ON_PAGE(memcg_data && !(memcg_data & MEMCG_DATA_OBJCGS), page); > + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, page); > > return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > } > @@ -454,6 +476,8 @@ static inline struct obj_cgroup > **page_objcgs_check(struct page *page) > if (!memcg_data || !(memcg_data & MEMCG_DATA_OBJCGS)) > return NULL; > > + VM_BUG_ON_PAGE(memcg_data & MEMCG_DATA_KMEM, page); > + > return (struct obj_cgroup **)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); > } > > @@ -1109,6 +1133,11 @@ static inline struct mem_cgroup > *page_memcg_check(struct page *page) > return NULL; > } > > +static inline bool PageMemcgKmem(struct page *page) > +{ > + return false; > +} > + > static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) > { > return true; > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index 4f6ba9379112..fc0e1bd48e73 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -715,9 +715,8 @@ PAGEFLAG_FALSE(DoubleMap) > #define PAGE_MAPCOUNT_RESERVE -128 > #define PG_buddy 0x00000080 > #define PG_offline 0x00000100 > -#define PG_kmemcg 0x00000200 > -#define PG_table 0x00000400 > -#define PG_guard 0x00000800 > +#define PG_table 0x00000200 > +#define PG_guard 0x00000400 > > #define PageType(page, flag) \ > ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) > @@ -768,12 +767,6 @@ PAGE_TYPE_OPS(Buddy, buddy) > */ > PAGE_TYPE_OPS(Offline, offline) > > -/* > - * If kmemcg is enabled, the buddy allocator will set PageKmemcg() on > - * pages allocated with __GFP_ACCOUNT. It gets cleared on page free. > - */ > -PAGE_TYPE_OPS(Kmemcg, kmemcg) > - > /* > * Marks pages in use as page tables. > */ > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index a8eb20283dcd..e3fc240101ff 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -3090,8 +3090,8 @@ int __memcg_kmem_charge_page(struct page *page, gfp_t > gfp, int order) > if (memcg && !mem_cgroup_is_root(memcg)) { > ret = __memcg_kmem_charge(memcg, gfp, 1 << order); > if (!ret) { > - page->memcg_data = (unsigned long)memcg; > - __SetPageKmemcg(page); > + page->memcg_data = (unsigned long)memcg | > + MEMCG_DATA_KMEM; > return 0; > } > css_put(&memcg->css); > @@ -3116,10 +3116,6 @@ void __memcg_kmem_uncharge_page(struct page *page, int > order) > __memcg_kmem_uncharge(memcg, nr_pages); > page->memcg_data = 0; > css_put(&memcg->css); > - > - /* slab pages do not have PageKmemcg flag set */ > - if (PageKmemcg(page)) > - __ClearPageKmemcg(page); > } > > static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int > nr_bytes) > @@ -6863,12 +6859,10 @@ static void uncharge_page(struct page *page, struct > uncharge_gather *ug) > nr_pages = compound_nr(page); > ug->nr_pages += nr_pages; > > - if (!PageKmemcg(page)) { > - ug->pgpgout++; > - } else { > + if (PageMemcgKmem(page)) > ug->nr_kmem += nr_pages; > - __ClearPageKmemcg(page); > - } > + else > + ug->pgpgout++; > > ug->dummy_page = page; > page->memcg_data = 0; > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e9f0fe4a143e..5ebd50183d93 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1179,7 +1179,7 @@ static __always_inline bool free_pages_prepare(struct > page *page, > * Do not let hwpoison pages hit pcplists/buddy > * Untie memcg state and reset page's owner > */ > - if (memcg_kmem_enabled() && PageKmemcg(page)) > + if (memcg_kmem_enabled() && PageMemcgKmem(page)) > __memcg_kmem_uncharge_page(page, order); > reset_page_owner(page, order); > return false; > @@ -1209,7 +1209,7 @@ static __always_inline bool free_pages_prepare(struct > page *page, > } > if (PageMappingFlags(page)) > page->mapping = NULL; > - if (memcg_kmem_enabled() && PageKmemcg(page)) > + if (memcg_kmem_enabled() && PageMemcgKmem(page)) > __memcg_kmem_uncharge_page(page, order); > if (check_free) > bad += check_free_page(page); > -- > 2.26.2 -- Michal Hocko SUSE Labs
