On Tue, Aug 21, 2018 at 2:36 PM Roman Gushchin <guro@xxxxxx> wrote:
>
> If CONFIG_VMAP_STACK is set, kernel stacks are allocated
> using __vmalloc_node_range() with __GFP_ACCOUNT. So kernel
> stack pages are charged against corresponding memory cgroups
> on allocation and uncharged on releasing them.
>
> The problem is that we do cache kernel stacks in small
> per-cpu caches and do reuse them for new tasks, which can
> belong to different memory cgroups.
>
> Each stack page still holds a reference to the original cgroup,
> so the cgroup can't be released until the vmap area is released.
>
> To make this happen we need more than two subsequent exits
> without forks in between on the current cpu, which makes it
> very unlikely to happen. As a result, I saw a significant number
> of dying cgroups (in theory, up to 2 * number_of_cpu +
> number_of_tasks), which can't be released even by significant
> memory pressure.
>
> As a cgroup structure can take a significant amount of memory
> (first of all, per-cpu data like memcg statistics), it leads
> to a noticeable waste of memory.
>
> Signed-off-by: Roman Gushchin <guro@xxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
BTW this makes a very good use-case for optimizing kmem uncharging
similar to what you did for skmem uncharging.
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
> ---
> include/linux/memcontrol.h | 13 +++++++++-
> kernel/fork.c | 51 +++++++++++++++++++++++++++++++++-----
> 2 files changed, 57 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 0e6c515fb698..b12a553048e2 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1250,10 +1250,11 @@ struct kmem_cache *memcg_kmem_get_cache(struct kmem_cache *cachep);
> void memcg_kmem_put_cache(struct kmem_cache *cachep);
> int memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
> struct mem_cgroup *memcg);
> +
> +#ifdef CONFIG_MEMCG_KMEM
> int memcg_kmem_charge(struct page *page, gfp_t gfp, int order);
> void memcg_kmem_uncharge(struct page *page, int order);
>
> -#ifdef CONFIG_MEMCG_KMEM
> extern struct static_key_false memcg_kmem_enabled_key;
> extern struct workqueue_struct *memcg_kmem_cache_wq;
>
> @@ -1289,6 +1290,16 @@ extern int memcg_expand_shrinker_maps(int new_id);
> extern void memcg_set_shrinker_bit(struct mem_cgroup *memcg,
> int nid, int shrinker_id);
> #else
> +
> +static inline int memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
> +{
> + return 0;
> +}
> +
> +static inline void memcg_kmem_uncharge(struct page *page, int order)
> +{
> +}
> +
> #define for_each_memcg_cache_index(_idx) \
> for (; NULL; )
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 5ee74c113381..09b5b9a40166 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -223,9 +223,14 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
> return s->addr;
> }
>
> + /*
> + * Allocated stacks are cached and later reused by new threads,
> + * so memcg accounting is performed manually on assigning/releasing
> + * stacks to tasks. Drop __GFP_ACCOUNT.
> + */
> stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
> VMALLOC_START, VMALLOC_END,
> - THREADINFO_GFP,
> + THREADINFO_GFP & ~__GFP_ACCOUNT,
> PAGE_KERNEL,
> 0, node, __builtin_return_address(0));
>
> @@ -248,9 +253,20 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
> static inline void free_thread_stack(struct task_struct *tsk)
> {
> #ifdef CONFIG_VMAP_STACK
> - if (task_stack_vm_area(tsk)) {
> + struct vm_struct *vm = task_stack_vm_area(tsk);
> +
> + if (vm) {
> int i;
>
> + for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
> + mod_memcg_page_state(vm->pages[i],
> + MEMCG_KERNEL_STACK_KB,
> + -(int)(PAGE_SIZE / 1024));
> +
> + memcg_kmem_uncharge(vm->pages[i],
> + compound_order(vm->pages[i]));
> + }
> +
> for (i = 0; i < NR_CACHED_STACKS; i++) {
> if (this_cpu_cmpxchg(cached_stacks[i],
> NULL, tsk->stack_vm_area) != NULL)
> @@ -350,10 +366,6 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
> NR_KERNEL_STACK_KB,
> PAGE_SIZE / 1024 * account);
> }
> -
> - /* All stack pages belong to the same memcg. */
> - mod_memcg_page_state(vm->pages[0], MEMCG_KERNEL_STACK_KB,
> - account * (THREAD_SIZE / 1024));
> } else {
> /*
> * All stack pages are in the same zone and belong to the
> @@ -369,6 +381,30 @@ static void account_kernel_stack(struct task_struct *tsk, int account)
> }
> }
>
> +static int memcg_charge_kernel_stack(struct task_struct *tsk)
> +{
> +#ifdef CONFIG_VMAP_STACK
> + struct vm_struct *vm = task_stack_vm_area(tsk);
> + int ret;
> +
> + if (vm) {
> + int i;
> +
> + for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
> + ret = memcg_kmem_charge(vm->pages[i], GFP_KERNEL,
> + compound_order(vm->pages[i]));
> + if (ret)
> + return ret;
> +
> + mod_memcg_page_state(vm->pages[i],
> + MEMCG_KERNEL_STACK_KB,
> + PAGE_SIZE / 1024);
> + }
> + }
> +#endif
> + return 0;
> +}
> +
> static void release_task_stack(struct task_struct *tsk)
> {
> if (WARN_ON(tsk->state != TASK_DEAD))
> @@ -807,6 +843,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> if (!stack)
> goto free_tsk;
>
> + if (memcg_charge_kernel_stack(tsk))
> + goto free_stack;
> +
> stack_vm_area = task_stack_vm_area(tsk);
>
> err = arch_dup_task_struct(tsk, orig);
> --
> 2.17.1
>
