From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f72.google.com (mail-oi0-f72.google.com [209.85.218.72]) by kanga.kvack.org (Postfix) with ESMTP id 74D0A6B0007 for ; Wed, 15 Aug 2018 13:16:32 -0400 (EDT) Received: by mail-oi0-f72.google.com with SMTP id t138-v6so1611398oih.5 for ; Wed, 15 Aug 2018 10:16:32 -0700 (PDT) Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com. [67.231.145.42]) by mx.google.com with ESMTPS id v125-v6si15973195oif.159.2018.08.15.10.16.31 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 15 Aug 2018 10:16:31 -0700 (PDT) Date: Wed, 15 Aug 2018 10:16:05 -0700 From: Roman Gushchin Subject: Re: [RFC PATCH 1/2] mm: rework memcg kernel stack accounting Message-ID: <20180815171605.GB26330@castle.DHCP.thefacebook.com> References: <20180815003620.15678-1-guro@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Shakeel Butt 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 06:18:01PM -0700, Shakeel Butt wrote: > 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. I also thought about having per-memcg stack cache, but it seems that caching 2 * n(cpus) * n(cgroups) stacks is an overkill, and there is nothing memcg-specific in these stacks except that they are pre-charged. > 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"). Sure, will do in v2. > > Reviewed-by: Shakeel Butt Thanks! > > > 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 > >