Re: [PATCH] perf: remove the extra validity check on nr_pages

[xiakaixu <xiakaixu@huawei.com>]

于 2015/1/27 17:55, Kaixu Xia 写道:
ping...

> The function is_power_of_2() also do the check on nr_pages,
> so the first check performed is unnecessary. On the other
> hand, the key point is to ensure @nr_pages is a power-of-two
> number and mostly @nr_pages is a nonzero value, so in the
> most cases, the function is_power_of_2() will be called.
> 
> Signed-off-by: Kaixu Xia <xiakaixu@huawei.com>
> ---
>  kernel/events/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 882f835..abb57c2 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4268,7 +4268,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
>  	 * If we have rb pages ensure they're a power-of-two number, so we
>  	 * can do bitmasks instead of modulo.
>  	 */
> -	if (nr_pages != 0 && !is_power_of_2(nr_pages))
> +	if (!is_power_of_2(nr_pages))
>  		return -EINVAL;
>  
>  	if (vma_size != PAGE_SIZE * (1 + nr_pages))
>