[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <ba60f1faab6c4469853f5bc31d1852c455268763.1468270393.git.luto@kernel.org>
Date: Mon, 11 Jul 2016 13:54:05 -0700
From: Andy Lutomirski <luto@...nel.org>
To: x86@...nel.org,
linux-kernel@...r.kernel.org
Cc: linux-arch@...r.kernel.org,
Borislav Petkov <bp@...en8.de>,
Nadav Amit <nadav.amit@...il.com>,
Kees Cook <keescook@...omium.org>,
Brian Gerst <brgerst@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Jann Horn <jann@...jh.net>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v5 32/32] 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 3003edae90fc..e8e21134ba23 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_kmem_pages((unsigned long)tsk->stack, THREAD_SIZE_ORDER);
+ return;
+ }
+#endif
+
+ free_kmem_pages((unsigned long)tsk->stack, THREAD_SIZE_ORDER);
}
# else
static struct kmem_cache *thread_stack_cache;
--
2.7.4
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
