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[209.85.220.65]) by mx.google.com with SMTPS id p4-v6sor7617041uae.116.2018.08.14.18.18.13 for (Google Transport Security); Tue, 14 Aug 2018 18:18:13 -0700 (PDT) MIME-Version: 1.0 References: <20180815003620.15678-1-guro@fb.com> In-Reply-To: <20180815003620.15678-1-guro@fb.com> From: Shakeel Butt Date: Tue, 14 Aug 2018 18:18:01 -0700 Message-ID: Subject: Re: [RFC PATCH 1/2] mm: rework memcg kernel stack accounting Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Roman Gushchin Cc: Linux MM , LKML , kernel-team@fb.com, Johannes Weiner , Michal Hocko , luto@kernel.org, koct9i@gmail.com, Tejun Heo On Tue, Aug 14, 2018 at 5:37 PM Roman Gushchin 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 I was also looking into this issue. I was thinking of having a per-memcg per-cpu stack cache. However this solution seems much simpler. Can you also add the performance number for a similar simple benchmark done in ac496bf48d97 ("fork: Optimize task creation by caching two thread stacks per CPU if CONFIG_VMAP_STACK=y"). Reviewed-by: Shakeel Butt > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Andy Lutomirski > Cc: Konstantin Khlebnikov > Cc: Tejun Heo > --- > kernel/fork.c | 44 ++++++++++++++++++++++++++++++++++++++------ > 1 file changed, 38 insertions(+), 6 deletions(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index 69b6fea5a181..91872b2b37bd 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -224,9 +224,14 @@ 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)); > > @@ -246,12 +251,41 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) > #endif > } > > +static void memcg_charge_kernel_stack(struct task_struct *tsk) > +{ > +#ifdef CONFIG_VMAP_STACK > + struct vm_struct *vm = task_stack_vm_area(tsk); > + > + if (vm) { > + int i; > + > + for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) > + memcg_kmem_charge(vm->pages[i], __GFP_NOFAIL, > + compound_order(vm->pages[i])); > + > + /* All stack pages belong to the same memcg. */ > + mod_memcg_page_state(vm->pages[0], MEMCG_KERNEL_STACK_KB, > + THREAD_SIZE / 1024); > + } > +#endif > +} > + > 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; > > + /* All stack pages belong to the same memcg. */ > + mod_memcg_page_state(vm->pages[0], MEMCG_KERNEL_STACK_KB, > + -(int)(THREAD_SIZE / 1024)); > + > + for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) > + 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) > @@ -352,10 +386,6 @@ 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 > @@ -809,6 +839,8 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) > if (!stack) > goto free_tsk; > > + memcg_charge_kernel_stack(tsk); > + > stack_vm_area = task_stack_vm_area(tsk); > > err = arch_dup_task_struct(tsk, orig); > -- > 2.14.4 >