On Thu, Jan 16, 2020 at 04:50:56PM +0100, Michal Hocko wrote: > [Cc Roman] Thanks! > > On Thu 16-01-20 09:10:11, Yafang Shao wrote: > > Per disccusion with Dave[1], we always assume we only ever put objects from > > memcg associated slab pages in the list_lru. In list_lru_from_kmem() it > > calls memcg_from_slab_page() which makes no attempt to verify the page is > > actually a slab page. But currently the binder coder (in > > drivers/android/binder_alloc.c) stores normal pages in the list_lru, rather > > than slab objects. The only reason the binder doesn't catch issue is that > > the list_lru is not configured to be memcg aware. > > In order to make it more stable, we should verify the page type before > > getting memcg from it. In this patch, a new helper is introduced and the > > old helper is modified. Now we have two helpers as bellow, > > > > struct mem_cgroup *__memcg_from_slab_page(struct page *page); > > struct mem_cgroup *memcg_from_slab_page(struct page *page); > > > > The first helper is used when we are sure the page is a slab page and also > > a head page, while the second helper is used when we are not sure the page > > type. > > > > [1]. > > https://lore.kernel.org/linux-mm/20200106213103.GJ23195@xxxxxxxxxxxxxxxxxxx/ > > > > Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx> > > Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx> Hello Yafang! I actually have something similar in my patch queue, but I'm adding a helper which takes a kernel pointer rather than a page: struct mem_cgroup *mem_cgroup_from_obj(void *p); Will it work for you? If so, I can send it separately. (I'm working on switching to per-object accounting of slab object, so that slab pages will be shared between multiple cgroups. So it will require a change like this). Thanks! -- >From fc2b1ec53285edcb0017275019d60bd577bf64a9 Mon Sep 17 00:00:00 2001 From: Roman Gushchin <guro@xxxxxx> Date: Thu, 2 Jan 2020 15:22:19 -0800 Subject: [PATCH] mm: memcg/slab: introduce mem_cgroup_from_obj() Sometimes we need to get a memcg pointer from a charged kernel object. The right way to do it depends on whether it's a proper slab object or it's backed by raw pages (e.g. it's a vmalloc alloction). In the first case the kmem_cache->memcg_params.memcg indirection should be used, however in the the second case it's just page->mem_cgroup. To simplify this task and hide these implementation details let's introduce the mem_cgroup_from_obj() helper, which takes a pointer to any kernel object and returns a valid memcg pointer or NULL. The caller is still responsible to ensure that the returned memcg isn't going away underneath: take the rcu read lock, cgroup mutex etc. mem_cgroup_from_kmem() defined in mm/list_lru.c is now obsolete and can be removed. Signed-off-by: Roman Gushchin <guro@xxxxxx> --- include/linux/memcontrol.h | 7 +++++++ mm/list_lru.c | 12 +----------- mm/memcontrol.c | 32 +++++++++++++++++++++++++++++--- 3 files changed, 37 insertions(+), 14 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index c372bed6be80..0f6f8e18029e 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -420,6 +420,8 @@ struct lruvec *mem_cgroup_page_lruvec(struct page *, struct pglist_data *); struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p); +struct mem_cgroup *mem_cgroup_from_obj(void *p); + struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm); struct mem_cgroup *get_mem_cgroup_from_page(struct page *page); @@ -912,6 +914,11 @@ static inline bool mm_match_cgroup(struct mm_struct *mm, return true; } +static inline struct mem_cgroup *mem_cgroup_from_obj(void *p) +{ + return NULL; +} + static inline struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm) { return NULL; diff --git a/mm/list_lru.c b/mm/list_lru.c index 0f1f6b06b7f3..8de5e3784ee4 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -57,16 +57,6 @@ list_lru_from_memcg_idx(struct list_lru_node *nlru, int idx) return &nlru->lru; } -static __always_inline struct mem_cgroup *mem_cgroup_from_kmem(void *ptr) -{ - struct page *page; - - if (!memcg_kmem_enabled()) - return NULL; - page = virt_to_head_page(ptr); - return memcg_from_slab_page(page); -} - static inline struct list_lru_one * list_lru_from_kmem(struct list_lru_node *nlru, void *ptr, struct mem_cgroup **memcg_ptr) @@ -77,7 +67,7 @@ list_lru_from_kmem(struct list_lru_node *nlru, void *ptr, if (!nlru->memcg_lrus) goto out; - memcg = mem_cgroup_from_kmem(ptr); + memcg = mem_cgroup_from_obj(ptr); if (!memcg) goto out; diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6e1ee8577ecf..99d6fe9d7026 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -757,13 +757,12 @@ void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val) { - struct page *page = virt_to_head_page(p); - pg_data_t *pgdat = page_pgdat(page); + pg_data_t *pgdat = page_pgdat(virt_to_page(p)); struct mem_cgroup *memcg; struct lruvec *lruvec; rcu_read_lock(); - memcg = memcg_from_slab_page(page); + memcg = mem_cgroup_from_obj(p); /* Untracked pages have no memcg, no lruvec. Update only the node */ if (!memcg || memcg == root_mem_cgroup) { @@ -2636,6 +2635,33 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg, unlock_page_lru(page, isolated); } +/* + * Returns a pointer to the memory cgroup to which the kernel object is charged. + * + * The caller must ensure the memcg lifetime, e.g. by owning a charged object, + * taking rcu_read_lock() or cgroup_mutex. + */ +struct mem_cgroup *mem_cgroup_from_obj(void *p) +{ + struct page *page; + + if (mem_cgroup_disabled()) + return NULL; + + page = virt_to_head_page(p); + + /* + * Slab pages don't have page->mem_cgroup set because corresponding + * kmem caches can be reparented during the lifetime. That's why + * cache->memcg_params.memcg pointer should be used instead. + */ + if (PageSlab(page)) + return memcg_from_slab_page(page); + + /* All other pages use page->mem_cgroup */ + return page->mem_cgroup; +} + #ifdef CONFIG_MEMCG_KMEM static int memcg_alloc_cache_id(void) { -- 2.21.1
