> From: Uros Bizjak <ubizjak@xxxxxxxxx>
> Subject: fork: use this_cpu_try_cmpxchg() in try_release_thread_stack_to_cache()
> Date: Thu, 23 May 2024 09:35:14 +0200
>
> Use this_cpu_try_cmpxchg() instead of this_cpu_cmpxchg (*ptr, old, new) ==
> old in try_release_thread_stack_to_cache. x86 CMPXCHG instruction returns
> success in ZF flag, so this change saves a compare after cmpxchg (and
> related move instruction in front of cmpxchg).
>
> No functional change intended.
Sorry, cosmetic nit...
> @@ -205,7 +205,9 @@ static bool try_release_thread_stack_to_
> unsigned int i;
>
> for (i = 0; i < NR_CACHED_STACKS; i++) {
> - if (this_cpu_cmpxchg(cached_stacks[i], NULL, vm) != NULL)
> + struct vm_struct *tmp = NULL;
> +
> + if (!this_cpu_try_cmpxchg(cached_stacks[i], &tmp, vm))
> continue;
> return true;
> }
Why not
static bool try_release_thread_stack_to_cache(struct vm_struct *vm)
{
unsigned int i;
for (i = 0; i < NR_CACHED_STACKS; i++) {
struct vm_struct *tmp = NULL;
if (this_cpu_try_cmpxchg(cached_stacks[i], &tmp, vm))
return true;
}
return false;
}
?
To me this "continue" just adds the unnecessary confusion with or without
this patch, but I won't insist.
Oleg.
