linux-kernel - Re: [PATCH v3] fork: free vmapped stacks in cache when cpus are offline

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Date:   Sat, 11 Feb 2017 00:00:00 +0900
From:   Hoeun Ryu <hoeun.ryu@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3] fork: free vmapped stacks in cache when cpus are offline

On Fri, Feb 10, 2017 at 11:41 PM, Michal Hocko <mhocko@...nel.org> wrote:
> On Fri 10-02-17 23:31:41, Hoeun Ryu wrote:
>> On Fri, Feb 10, 2017 at 9:05 PM, Michal Hocko <mhocko@...nel.org> wrote:
>> > On Fri 10-02-17 17:32:07, Hoeun Ryu wrote:
> [...]
>> >>  static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
>> >> @@ -456,6 +474,11 @@ void __init fork_init(void)
>> >>       for (i = 0; i < UCOUNT_COUNTS; i++) {
>> >>               init_user_ns.ucount_max[i] = max_threads/2;
>> >>       }
>> >> +
>> >> +#ifdef CONFIG_VMAP_STACK
>> >> +     cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "vm_stack_cache",
>> >> +                       NULL, free_vm_stack_cache);
>> >> +#endif
>> >
>> > I am not familiar the new hotplug infrastructure so I might be missing
>> > something. CPUHP_AP_ONLINE_DYN will allocate a state which is has only
>> > 30 slots available. The name also suggests this will be called on an
>> > online event. Why doesn't this have its own state like other users. The
>> > name should also reflect offline event CPUHP_STACK_CACHE_DEAD or
>> > something like that.
>>
>> I'll define CPUHP_VMSTACK_CACHE_DEAD before CPUHP_BP_PREPARE_DYN in
>> cpuhotplug.h.
>> Do you think the change is made in a separate patch or not ?
>
> I think it should be in a single patch. I am not sure what are the rules
> to define a new state though. Let's CC Thomas.

OK, I will.

> --
> Michal Hocko
> SUSE Labs