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Message-ID: <20170211063445.GB30713@dhcp22.suse.cz>
Date: Sat, 11 Feb 2017 07:34:45 +0100
From: Michal Hocko <mhocko@...nel.org>
To: Hoeun Ryu <hoeun.ryu@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>, Andy Lutomirski <luto@...nel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Oleg Nesterov <oleg@...hat.com>, Mateusz Guzik <mguzik@...hat.com>,
linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v4] fork: free vmapped stacks in cache when cpus are
offline
On Sat 11-02-17 08:40:38, 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@...il.com>
Acked-by: Michal Hocko <mhocko@...e.com>
> ---
> v4:
> use CPUHP_BP_PREPARE_DYN state for cpuhp setup
> fix minor coding style
> v3:
> fix misuse of per-cpu api
> fix location of function definition within CONFIG_VMAP_STACK
> v2:
> remove cpuhp callback for `startup`, only `teardown` callback is installed.
>
> kernel/fork.c | 23 +++++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 937ba59..61634d7 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -168,6 +168,24 @@ void __weak arch_release_thread_stack(unsigned long *stack)
> */
> #define NR_CACHED_STACKS 2
> static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]);
> +
> +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)
> + continue;
> +
> + vfree(vm_stack->addr);
> + cached_vm_stacks[i] = NULL;
> + }
> +
> + 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_BP_PREPARE_DYN, "fork:vmstack_cache",
> + NULL, free_vm_stack_cache);
> +#endif
> }
>
> int __weak arch_dup_task_struct(struct task_struct *dst,
> --
> 2.7.4
>
--
Michal Hocko
SUSE Labs
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