From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 001D26B2AF7 for ; Thu, 23 Aug 2018 12:24:09 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id g5-v6so2529944edp.1 for ; Thu, 23 Aug 2018 09:24:09 -0700 (PDT) Received: from mx0a-00082601.pphosted.com (mx0b-00082601.pphosted.com. [67.231.153.30]) by mx.google.com with ESMTPS id p1-v6si10230edq.94.2018.08.23.09.24.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 23 Aug 2018 09:24:08 -0700 (PDT) Date: Thu, 23 Aug 2018 09:23:50 -0700 From: Roman Gushchin Subject: Re: [PATCH v2 1/3] mm: rework memcg kernel stack accounting Message-ID: <20180823162347.GA22650@tower.DHCP.thefacebook.com> References: <20180821213559.14694-1-guro@fb.com> <20180822141213.GO29735@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20180822141213.GO29735@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, Johannes Weiner , Andy Lutomirski , Konstantin Khlebnikov , Tejun Heo , Shakeel Butt On Wed, Aug 22, 2018 at 04:12:13PM +0200, Michal Hocko wrote: > On Tue 21-08-18 14:35:57, 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 > > Cc: Johannes Weiner > > Cc: Michal Hocko > > Cc: Andy Lutomirski > > Cc: Konstantin Khlebnikov > > Cc: Tejun Heo > > Cc: Shakeel Butt > > Looks good to me. Two nits below. > > I am not sure stable tree backport is really needed but it would be nice > to put > Fixes: ac496bf48d97 ("fork: Optimize task creation by caching two thread stacks per CPU if CONFIG_VMAP_STACK=y") > > Acked-by: Michal Hocko Will add, thanks! > > > @@ -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])); > > when do we have order > 0 here? I guess, it's not possible, but hard-coded 1 looked a bit crappy. Do you think it's better? > Also I was wondering how come this > doesn't blow up on partially charged stacks but both > mod_memcg_page_state and memcg_kmem_uncharge check for page->mem_cgroup > so this is safe. Maybe a comment would save people from scratching their > heads. Ok, will add. Thank you!