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

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

[Kaixu Xia]

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))
-- 
1.8.5.5

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

[xiakaixu]

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))
> 

[tip:perf/core] perf: Remove the extra validity check on nr_pages

[tip-bot for Kaixu Xia]

Commit-ID:  74390aa5567827add5058a3b26eff0ed06a629ba
Gitweb:     http://git.kernel.org/tip/74390aa5567827add5058a3b26eff0ed06a629ba
Author:     Kaixu Xia <xiakaixu@huawei.com>
AuthorDate: Tue, 27 Jan 2015 17:55:12 +0800
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Fri, 13 Feb 2015 11:40:30 -0300

perf: Remove the extra validity check on nr_pages

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>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Link: http://lkml.kernel.org/r/1422352512-75150-1-git-send-email-xiakaixu@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.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 7f2fbb8..0969c9b 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4420,7 +4420,7 @@ 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))