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fork: Optimize task creation by caching two thread stacks per CPU if CONFIG_VMAP_STACK=y 

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=y, 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@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jann Horn <jann@thejh.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/94811d8e3994b2e962f88866290017d498eb069c.1474003868.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2016-09-15 22:45:49 -07:00 committed by Ingo Molnar
parent 68f24b08ee
commit ac496bf48d
1 changed files with 53 additions and 9 deletions
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62
kernel/fork.c
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@ -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;