Messages in this thread | | | From | Hoeun Ryu <> | Date | Thu, 9 Feb 2017 22:36:04 +0900 | Subject | Re: [PATCH v2 1/2] fork: free vmapped stacks in cache when cpus are offline |
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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
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