From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f200.google.com (mail-pf1-f200.google.com [209.85.210.200]) by kanga.kvack.org (Postfix) with ESMTP id C78156B41FE for ; Mon, 27 Aug 2018 17:01:46 -0400 (EDT) Received: by mail-pf1-f200.google.com with SMTP id h65-v6so186340pfk.18 for ; Mon, 27 Aug 2018 14:01:46 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id p126-v6si296659pfb.77.2018.08.27.14.01.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 27 Aug 2018 14:01:45 -0700 (PDT) Date: Mon, 27 Aug 2018 14:01:43 -0700 From: Andrew Morton Subject: Re: [PATCH v3 1/3] mm: rework memcg kernel stack accounting Message-Id: <20180827140143.98b65bc7cb32f50245eb9114@linux-foundation.org> In-Reply-To: <20180827162621.30187-1-guro@fb.com> References: <20180827162621.30187-1-guro@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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, Shakeel Butt , Michal Hocko , Johannes Weiner , Andy Lutomirski , Konstantin Khlebnikov , Tejun Heo On Mon, 27 Aug 2018 09:26:19 -0700 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. OK, but this doesn't describe how the patch addresses this issue? > > ... > > @@ -371,6 +382,35 @@ 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++) { Can we ever have THREAD_SIZE < PAGE_SIZE? 64k pages? > + /* > + * If memcg_kmem_charge() fails, page->mem_cgroup > + * pointer is NULL, and both memcg_kmem_uncharge() > + * and mod_memcg_page_state() in free_thread_stack() > + * will ignore this page. So it's safe. > + */ > + ret = memcg_kmem_charge(vm->pages[i], GFP_KERNEL, 0); > + if (ret) > + return ret; > + > + mod_memcg_page_state(vm->pages[i], > + MEMCG_KERNEL_STACK_KB, > + PAGE_SIZE / 1024); > + } > + } > +#endif > + return 0; > +} > > ... >