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 09B686B1FDA for ; Tue, 21 Aug 2018 13:23:02 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id y8-v6so7195235edr.12 for ; Tue, 21 Aug 2018 10:23:01 -0700 (PDT) Received: from mx0a-00082601.pphosted.com (mx0b-00082601.pphosted.com. [67.231.153.30]) by mx.google.com with ESMTPS id b38-v6si4497708ede.355.2018.08.21.10.23.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 Aug 2018 10:23:00 -0700 (PDT) Date: Tue, 21 Aug 2018 10:22:39 -0700 From: Roman Gushchin Subject: Re: [RFC PATCH 1/2] mm: rework memcg kernel stack accounting Message-ID: <20180821172236.GA27058@tower.DHCP.thefacebook.com> References: <20180815003620.15678-1-guro@fb.com> <20180815163923.GA28953@cmpxchg.org> <20180815165513.GA26330@castle.DHCP.thefacebook.com> <2393E780-2B97-4BEE-8374-8E9E5249E5AD@amacapital.net> <20180815172557.GC26330@castle.DHCP.thefacebook.com> <19CD1E5B-CB86-493A-8BA6-7389E36291B4@amacapital.net> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <19CD1E5B-CB86-493A-8BA6-7389E36291B4@amacapital.net> Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: Shakeel Butt , Johannes Weiner , Linux MM , LKML , kernel-team@fb.com, Michal Hocko , luto@kernel.org, Konstantin Khlebnikov , Tejun Heo On Wed, Aug 15, 2018 at 10:37:28AM -0700, Andy Lutomirski wrote: > > > > On Aug 15, 2018, at 10:32 AM, Shakeel Butt wrote: > > > >> On Wed, Aug 15, 2018 at 10:26 AM Roman Gushchin wrote: > >> > >>> On Wed, Aug 15, 2018 at 10:12:42AM -0700, Andy Lutomirski wrote: > >>> > >>> > >>>>> On Aug 15, 2018, at 9:55 AM, Roman Gushchin wrote: > >>>>> > >>>>>> On Wed, Aug 15, 2018 at 12:39:23PM -0400, Johannes Weiner wrote: > >>>>>> On Tue, Aug 14, 2018 at 05:36:19PM -0700, Roman Gushchin wrote: > >>>>>> @@ -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 > >>>>>> +} > >>>>> > >>>>> Before this change, the memory limit can fail the fork, but afterwards > >>>>> fork() can grow memory consumption unimpeded by the cgroup settings. > >>>>> > >>>>> Can we continue to use try_charge() here and fail the fork? > >>>> > >>>> We can, but I'm not convinced we should. > >>>> > >>>> Kernel stack is relatively small, and it's already allocated at this point. > >>>> So IMO exceeding the memcg limit for 1-2 pages isn't worse than > >>>> adding complexity and handle this case (e.g. uncharge partially > >>>> charged stack). Do you have an example, when it does matter? > >>> > >>> What bounds it to just a few pages? Couldna??t there be lots of forks in flight that all hit this path? Ita??s unlikely, and there are surely easier DoS vectors, but still. > >> > >> Because any following memcg-aware allocation will fail. > >> There is also the pid cgroup controlled which can be used to limit the number > >> of forks. > >> > >> Anyway, I'm ok to handle the this case and fail fork, > >> if you think it does matter. > > > > Roman, before adding more changes do benchmark this. Maybe disabling > > the stack caching for CONFIG_MEMCG is much cleaner. > > > > > > Unless memcg accounting is colossally slow, the caching should be left on. vmalloc() isna??t inherently slow, but vfree() is, since we need to do a global broadcast TLB flush after enough vfree() calls. It's not. BTW, is the test, which you used to measure the performance gains of stack caching, available publicly? Thanks!