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SubjectRe: [PATCH v3] fork: free vmapped stacks in cache when cpus are offline
On Fri, Feb 10, 2017 at 9:05 PM, Michal Hocko <mhocko@kernel.org> wrote:
> On Fri 10-02-17 17:32:07, Hoeun Ryu wrote:
> [...]
>> +static int free_vm_stack_cache(unsigned int cpu)
>> +{
>> + struct vm_struct **cached_vm_stacks = per_cpu_ptr(cached_stacks, cpu);
>> + int i;
>> +
>> + for (i = 0; i < NR_CACHED_STACKS; i++) {
>> + struct vm_struct **vm_stack = &cached_vm_stacks[i];
>> +
>> + if (*vm_stack == NULL)
>> + continue;
>> +
>> + vfree((*vm_stack)->addr);
>> + *vm_stack = NULL;
>
> this seems more obscure than necessary. Probably a matter of taste but I
> would find the following easier to read
> struct vm_struct *vm_stack = cached_vm_stacks[i];
>
> if (!vm_stack)
> continue;
>
> vfree(vm_stack);
> cached_vm_stacks[i] = NULL;
>

OK, it's easier to read, I'll fix it.

>> + }
>> +
>> + return 0;
>> +}
>> #endif
>>
>> 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 ?

Thank you for your review anyway.

>
> --
> Michal Hocko
> SUSE Labs

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