linux-kernel - Re: [PATCH] perf: remove the extra validity check on nr

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Message-ID: <54CAE316.1070300@huawei.com>
Date:	Fri, 30 Jan 2015 09:49:10 +0800
From:	xiakaixu <xiakaixu@...wei.com>
To:	Kaixu Xia <xiakaixu@...wei.com>, <a.p.zijlstra@...llo.nl>,
	<paulus@...ba.org>, <mingo@...hat.com>, <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>
CC:	<linux-kernel@...r.kernel.org>, <kaixu.xia@...aro.org>
Subject: Re: [PATCH] perf: remove the extra validity check on nr_pages

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@...wei.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))
> 


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