From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id D18876B0003 for ; Wed, 15 Aug 2018 03:11:00 -0400 (EDT) Received: by mail-ed1-f69.google.com with SMTP id i26-v6so261899edr.4 for ; Wed, 15 Aug 2018 00:11:00 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id n38-v6si683918edn.443.2018.08.15.00.10.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 15 Aug 2018 00:10:59 -0700 (PDT) Date: Wed, 15 Aug 2018 09:10:58 +0200 From: Michal Hocko Subject: Re: [RFC PATCH 1/2] mm: rework memcg kernel stack accounting Message-ID: <20180815071058.GL32645@dhcp22.suse.cz> References: <20180815003620.15678-1-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180815003620.15678-1-guro@fb.com> Sender: owner-linux-mm@kvack.org List-ID: To: Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Johannes Weiner , Andy Lutomirski , Konstantin Khlebnikov , Tejun Heo On Tue 14-08-18 17:36:19, 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 Fixes: ac496bf48d97 ("fork: Optimize task creation by caching two thread stacks per CPU if CONFIG_VMAP_STACK=y") AFAICS > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Andy Lutomirski > Cc: Konstantin Khlebnikov > Cc: Tejun Heo Yes this is the right way to do accounting here. Acked-by: Michal Hocko Thanks! > --- > 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 -- Michal Hocko SUSE Labs