Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1577589

Re: [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline

Show all headers | View raw

On Thu, Feb 9, 2017 at 5:38 PM, Michal Hocko <mhocko@kernel.org> wrote:
> On Thu 09-02-17 13:03:46, Hoeun Ryu wrote:
>>  Using virtually mapped stack, kernel stacks are allocated via vmalloc.
>> In the current implementation, two stacks per cpu can be cached when
>> tasks are freed and the cached stacks are used again in task duplications.
>> but the cached stacks may remain unfreed even when cpu are offline.
>>  By adding a cpu hotplug callback to free the cached stacks when a cpu
>> goes offline, the pages of the cached stacks are not wasted.
>>
>> Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com>
>> ---
>> Changes in v2:
>>  remove cpuhp callback for `starup`, only `teardown` callback is installed.
>>
>>  kernel/fork.c | 21 +++++++++++++++++++++
>>  1 file changed, 21 insertions(+)
>>
>> diff --git a/kernel/fork.c b/kernel/fork.c
>> index 61284d8..7911ed2 100644
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -170,6 +170,22 @@ void __weak arch_release_thread_stack(unsigned long *stack)
>>  static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
>>  #endif
>>
>> +static int free_vm_stack_cache(unsigned int cpu)
>> +{
>> +     int i;
>> +
>> +     for (i = 0; i < NR_CACHED_STACKS; i++) {
>> +             struct vm_struct *vm_stack = this_cpu_read(cached_stacks[i]);
>
> the callbak will run on the given cpu so this_cpu_read will be in fact
> per_cpu_ptr(cached_stacks[i], cpu). Using this_cpu_read is just too
> confusing. Also you do want to make this function defined only for
> CONFIG_VMAP_STACK.
>

Sorry, Thank you for your correction. I will fix this.

>> +             if (!vm_stack)
>> +                     continue;
>> +
>> +             vfree(vm_stack->addr);
>> +             this_cpu_write(cached_stacks[i], NULL);
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>
> --
> Michal Hocko
> SUSE Labs

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline Hoeun Ryu <hoeun.ryu@gmail.com> - 2017-02-09 05:20 +0100
  Re: [kernel-hardening] [PATCH v2 2/2] fork: make number of cached  stacks (vmapped) configurable using Kbuild Eric Biggers <ebiggers3@gmail.com> - 2017-02-09 05:30 +0100
  [PATCH v2 2/2] fork: make number of cached stacks (vmapped) configurable using Kbuild Hoeun Ryu <hoeun.ryu@gmail.com> - 2017-02-09 05:40 +0100
    Re: [PATCH v2 2/2] fork: make number of cached stacks (vmapped)  configurable using Kbuild Michal Hocko <mhocko@kernel.org> - 2017-02-09 09:50 +0100
      Re: [PATCH v2 2/2] fork: make number of cached stacks (vmapped)  configurable using Kbuild Hoeun Ryu <hoeun.ryu@gmail.com> - 2017-02-09 14:40 +0100
  Re: [kernel-hardening] [PATCH v2 1/2] fork: free vmapped stacks in  cache when cpus are offline Eric Biggers <ebiggers3@gmail.com> - 2017-02-09 06:00 +0100
    Re: [kernel-hardening] [PATCH v2 1/2] fork: free vmapped stacks in  cache when cpus are offline Hoeun Ryu <hoeun.ryu@gmail.com> - 2017-02-09 14:40 +0100
  Re: [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are  offline kbuild test robot <lkp@intel.com> - 2017-02-09 08:40 +0100
  Re: [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are  offline Michal Hocko <mhocko@kernel.org> - 2017-02-09 10:00 +0100
    Re: [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline Hoeun Ryu <hoeun.ryu@gmail.com> - 2017-02-09 14:40 +0100
  Re: [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are  offline kbuild test robot <lkp@intel.com> - 2017-02-09 11:20 +0100

csiph-web