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Date: Thu, 15 Sep 2016 22:45:49 -0700 From: Andy Lutomirski <luto@...nel.org> To: x86@...nel.org Cc: Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org, Brian Gerst <brgerst@...il.com>, Jann Horn <jann@...jh.net>, Josh Poimboeuf <jpoimboe@...hat.com>, Andy Lutomirski <luto@...nel.org> Subject: [PATCH v2 8/8] fork: Cache two thread stacks per cpu if CONFIG_VMAP_STACK is set vmalloc is a bit slow, and pounding vmalloc/vfree will eventually force a global TLB flush. To reduce pressure on them, if CONFIG_VMAP_STACK, cache two thread stacks per cpu. This will let us quickly allocate a hopefully cache-hot, TLB-hot stack under heavy forking workloads (shell script style). On my silly pthread_create benchmark, it saves about 2 µs per pthread_create+join with CONFIG_VMAP_STACK=y. Signed-off-by: Andy Lutomirski <luto@...nel.org> --- kernel/fork.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 53 insertions(+), 9 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 5dd0a516626d..2d44a9d05218 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -159,15 +159,41 @@ void __weak arch_release_thread_stack(unsigned long *stack) * kmemcache based allocator. */ # if THREAD_SIZE >= PAGE_SIZE || defined(CONFIG_VMAP_STACK) + +#ifdef CONFIG_VMAP_STACK +/* + * vmalloc is a bit slow, and calling vfree enough times will force a TLB + * flush. Try to minimize the number of calls by caching stacks. + */ +#define NR_CACHED_STACKS 2 +static DEFINE_PER_CPU(struct vm_struct *, cached_stacks[NR_CACHED_STACKS]); +#endif + static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) { #ifdef CONFIG_VMAP_STACK - void *stack = __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE, - VMALLOC_START, VMALLOC_END, - THREADINFO_GFP | __GFP_HIGHMEM, - PAGE_KERNEL, - 0, node, - __builtin_return_address(0)); + void *stack; + int i; + + local_irq_disable(); + for (i = 0; i < NR_CACHED_STACKS; i++) { + struct vm_struct *s = this_cpu_read(cached_stacks[i]); + + if (!s) + continue; + this_cpu_write(cached_stacks[i], NULL); + + tsk->stack_vm_area = s; + local_irq_enable(); + return s->addr; + } + local_irq_enable(); + + stack = __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE, + VMALLOC_START, VMALLOC_END, + THREADINFO_GFP | __GFP_HIGHMEM, + PAGE_KERNEL, + 0, node, __builtin_return_address(0)); /* * We can't call find_vm_area() in interrupt context, and @@ -187,10 +213,28 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node) static inline void free_thread_stack(struct task_struct *tsk) { - if (task_stack_vm_area(tsk)) +#ifdef CONFIG_VMAP_STACK + if (task_stack_vm_area(tsk)) { + unsigned long flags; + int i; + + local_irq_save(flags); + for (i = 0; i < NR_CACHED_STACKS; i++) { + if (this_cpu_read(cached_stacks[i])) + continue; + + this_cpu_write(cached_stacks[i], tsk->stack_vm_area); + local_irq_restore(flags); + return; + } + local_irq_restore(flags); + vfree(tsk->stack); - else - __free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER); + return; + } +#endif + + __free_pages(virt_to_page(tsk->stack), THREAD_SIZE_ORDER); } # else static struct kmem_cache *thread_stack_cache; -- 2.7.4
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