On Sat, Mar 21, 2020 at 04:48:56PM -0700, Andrew Morton wrote:

On Tue, 3 Mar 2020 15:35:50 -0800 Roman Gushchin guro@fb.com wrote:

...

Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio the space for task stacks can be allocated using __vmalloc_node_range(), alloc_pages_node() and kmem_cache_alloc_node(). In the first and the second cases page->mem_cgroup pointer is set, but in the third it's not: memcg membership of a slab page should be determined using the memcg_from_slab_page() function, which looks at page->slab_cache->memcg_params.memcg . In this case, using mod_memcg_page_state() (as in account_kernel_stack()) is incorrect: page->mem_cgroup pointer is NULL even for pages charged to a non-root memory cgroup.

It can lead to kernel_stack per-memcg counters permanently showing 0 on some architectures (depending on the configuration).

In order to fix it, let's introduce a mod_memcg_obj_state() helper, which takes a pointer to a kernel object as a first argument, uses mem_cgroup_from_obj() to get a RCU-protected memcg pointer and calls mod_memcg_state(). It allows to handle all possible configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE values) without spilling any memcg/kmem specifics into fork.c .

Note: this patch has been first posted as a part of the new slab controller patchset. This is a slightly updated version: the fixes tag has been added and the commit log was extended by the advice of Johannes Weiner. Because it's a fix that makes sense by itself, I'm re-posting it as a standalone patch.

Actually, it isn't a standalone patch.

...

--- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -776,6 +776,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val) rcu_read_unlock(); } +void mod_memcg_obj_state(void *p, int idx, int val) +{

• struct mem_cgroup *memcg;
• rcu_read_lock();
• memcg = mem_cgroup_from_obj(p);
• if (memcg)

• mod_memcg_state(memcg, idx, val);
  

• rcu_read_unlock();

+}

mem_cgroup_from_obj() is later added by http://lkml.kernel.org/r/20200117203609.3146239-1-guro@fb.com

We could merge both mm-memcg-slab-introduce-mem_cgroup_from_obj.patch and this patch, but that's a whole lot of stuff to backport into -stable.

Are you able to come up with a simpler suitable-for-stable fix?

How about this one? I've merged them into one and stripped it a little bit.

Thanks!

--

From 1b8b039b05d49945aaf34a0600b04ea616fe0ba2 Mon Sep 17 00:00:00 2001

From: Roman Gushchin guro@fb.com Date: Sat, 21 Mar 2020 23:05:42 +0000 Subject: [PATCH] mm: fork: fix kernel_stack memcg stats for various stack implementations

Depending on CONFIG_VMAP_STACK and the THREAD_SIZE / PAGE_SIZE ratio the space for task stacks can be allocated using __vmalloc_node_range(), alloc_pages_node() and kmem_cache_alloc_node(). In the first and the second cases page->mem_cgroup pointer is set, but in the third it's not: memcg membership of a slab page should be determined using the memcg_from_slab_page() function, which looks at page->slab_cache->memcg_params.memcg . In this case, using mod_memcg_page_state() (as in account_kernel_stack()) is incorrect: page->mem_cgroup pointer is NULL even for pages charged to a non-root memory cgroup.

It can lead to kernel_stack per-memcg counters permanently showing 0 on some architectures (depending on the configuration).

In order to fix it, let's introduce a mod_memcg_obj_state() helper, which takes a pointer to a kernel object as a first argument, uses mem_cgroup_from_obj() to get a RCU-protected memcg pointer and calls mod_memcg_state(). It allows to handle all possible configurations (CONFIG_VMAP_STACK and various THREAD_SIZE/PAGE_SIZE values) without spilling any memcg/kmem specifics into fork.c .

Note: This is a special version of the patch created for stable backports. It contains code from the following two patches: - mm: memcg/slab: introduce mem_cgroup_from_obj() - mm: fork: fix kernel_stack memcg stats for various stack implementations

Fixes: 4d96ba353075 ("mm: memcg/slab: stop setting page->mem_cgroup pointer for slab pages") Signed-off-by: Roman Gushchin guro@fb.com Cc: stable@vger.kernel.org --- include/linux/memcontrol.h | 12 ++++++++++++ kernel/fork.c | 4 ++-- mm/memcontrol.c | 38 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index a7a0a1a5c8d5..e9ba01336d4e 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -695,6 +695,7 @@ static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec, void __mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, int val); void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val); +void mod_memcg_obj_state(void *p, int idx, int val);

static inline void mod_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, int val) @@ -1123,6 +1124,10 @@ static inline void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, __mod_node_page_state(page_pgdat(page), idx, val); }

+static inline void mod_memcg_obj_state(void *p, int idx, int val) +{ +} + static inline unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order, gfp_t gfp_mask, @@ -1427,6 +1432,8 @@ static inline int memcg_cache_id(struct mem_cgroup *memcg) return memcg ? memcg->kmemcg_id : -1; }

+struct mem_cgroup *mem_cgroup_from_obj(void *p); + #else

static inline int memcg_kmem_charge(struct page *page, gfp_t gfp, int order) @@ -1468,6 +1475,11 @@ static inline void memcg_put_cache_ids(void) { }

+static inline struct mem_cgroup *mem_cgroup_from_obj(void *p) +{ + return NULL; +} + #endif /* CONFIG_MEMCG_KMEM */

#endif /* _LINUX_MEMCONTROL_H */ diff --git a/kernel/fork.c b/kernel/fork.c index 080809560072..183a6722dfe2 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -397,8 +397,8 @@ static void account_kernel_stack(struct task_struct *tsk, int account) mod_zone_page_state(page_zone(first_page), NR_KERNEL_STACK_KB, THREAD_SIZE / 1024 * account);

- mod_memcg_page_state(first_page, MEMCG_KERNEL_STACK_KB, - account * (THREAD_SIZE / 1024)); + mod_memcg_obj_state(stack, MEMCG_KERNEL_STACK_KB, + account * (THREAD_SIZE / 1024)); } }

diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6c83cf4ed970..a0aa1c213231 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -775,6 +775,17 @@ void __mod_lruvec_slab_state(void *p, enum node_stat_item idx, int val) rcu_read_unlock(); }

+void mod_memcg_obj_state(void *p, int idx, int val) +{ + struct mem_cgroup *memcg; + + rcu_read_lock(); + memcg = mem_cgroup_from_obj(p); + if (memcg) + mod_memcg_state(memcg, idx, val); + rcu_read_unlock(); +} + /** * __count_memcg_events - account VM events in a cgroup * @memcg: the memory cgroup @@ -2636,6 +2647,33 @@ static void commit_charge(struct page *page, struct mem_cgroup *memcg, }

#ifdef CONFIG_MEMCG_KMEM +/* + * Returns a pointer to the memory cgroup to which the kernel object is charged. + * + * The caller must ensure the memcg lifetime, e.g. by taking rcu_read_lock(), + * cgroup_mutex, etc. + */ +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 + * memcg_from_slab_page() should be used instead. + */ + if (PageSlab(page)) + return memcg_from_slab_page(page); + + /* All other pages use page->mem_cgroup */ + return page->mem_cgroup; +} + static int memcg_alloc_cache_id(void) { int id, size;

On Mon, 23 Mar 2020 18:03:58 -0700 Andrew Morton akpm@linux-foundation.org wrote:

On Mon, 23 Mar 2020 17:42:21 -0700 Roman Gushchin guro@fb.com wrote:

...

How about this one? I've merged them into one and stripped it a little bit.

Thanks!

Yes, that looks good. Here's the delta from the previously reviewed version. I think it's valid to retain those acks and revewed-by's.

And here's the altered "mm: memcg/slab: introduce mem_cgroup_from_obj()", which I have renamed to "mm: memcg/slab: use mem_cgroup_from_obj()":

The end result is slightly different - mem_cgroup_from_obj() will now end up inside #ifdef CONFIG_MEMCG_KMEM. Should I undo that?

From: Roman Gushchin guro@fb.com Subject: mm: memcg/slab: use mem_cgroup_from_obj()

Sometimes we need to get a memcg pointer from a charged kernel object. The right way to get 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; in other cases it's just page->mem_cgroup.

To simplify this task and hide the implementation details let's use the mem_cgroup_from_obj() helper, which takes a pointer to any kernel object and returns a valid memcg pointer or NULL.

Passing a kernel address rather than a pointer to a page will allow to use this helper for per-object (rather than per-page) tracked objects in the future.

The caller is still responsible to ensure that the returned memcg isn't going away underneath: take the rcu read lock, cgroup mutex etc; depending on the context.

mem_cgroup_from_kmem() defined in mm/list_lru.c is now obsolete and can be removed.

Link: http://lkml.kernel.org/r/20200117203609.3146239-1-guro@fb.com Signed-off-by: Roman Gushchin guro@fb.com Acked-by: Yafang Shao laoar.shao@gmail.com Reviewed-by: Shakeel Butt shakeelb@google.com Cc: Michal Hocko mhocko@kernel.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Vladimir Davydov vdavydov.dev@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/list_lru.c | 12 +----------- mm/memcontrol.c | 5 ++--- 2 files changed, 3 insertions(+), 14 deletions(-)

--- a/mm/list_lru.c~mm-memcg-slab-introduce-mem_cgroup_from_obj +++ a/mm/list_lru.c @@ -57,16 +57,6 @@ list_lru_from_memcg_idx(struct list_lru_ 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 if (!nlru->memcg_lrus) goto out;

- memcg = mem_cgroup_from_kmem(ptr); + memcg = mem_cgroup_from_obj(ptr); if (!memcg) goto out;

--- a/mm/memcontrol.c~mm-memcg-slab-introduce-mem_cgroup_from_obj +++ a/mm/memcontrol.c @@ -759,13 +759,12 @@ void __mod_lruvec_state(struct lruvec *l

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) { _