[PATCH linux-next] mm/huge_memory: remove redundant locking when parsing THP sysfs input

[PATCH linux-next] mm/huge_memory: remove redundant locking when parsing THP sysfs input

[xu.xin16]

From: Ran Xiaokai <ran.xiaokai@zte.com.cn>

Since sysfs_streq() only performs a simple memory comparison operation
and will not introduce any sleepable operation, So there is no
need to drop the lock when parsing input. Remove redundant lock
and unlock operations to make code cleaner.

Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
---
 mm/huge_memory.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 89f58c7603b2..87123a87cb21 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -478,32 +478,26 @@ static ssize_t thpsize_enabled_store(struct kobject *kobj,
 	int order = to_thpsize(kobj)->order;
 	ssize_t ret = count;

+	spin_lock(&huge_anon_orders_lock);
 	if (sysfs_streq(buf, "always")) {
-		spin_lock(&huge_anon_orders_lock);
 		clear_bit(order, &huge_anon_orders_inherit);
 		clear_bit(order, &huge_anon_orders_madvise);
 		set_bit(order, &huge_anon_orders_always);
-		spin_unlock(&huge_anon_orders_lock);
 	} else if (sysfs_streq(buf, "inherit")) {
-		spin_lock(&huge_anon_orders_lock);
 		clear_bit(order, &huge_anon_orders_always);
 		clear_bit(order, &huge_anon_orders_madvise);
 		set_bit(order, &huge_anon_orders_inherit);
-		spin_unlock(&huge_anon_orders_lock);
 	} else if (sysfs_streq(buf, "madvise")) {
-		spin_lock(&huge_anon_orders_lock);
 		clear_bit(order, &huge_anon_orders_always);
 		clear_bit(order, &huge_anon_orders_inherit);
 		set_bit(order, &huge_anon_orders_madvise);
-		spin_unlock(&huge_anon_orders_lock);
 	} else if (sysfs_streq(buf, "never")) {
-		spin_lock(&huge_anon_orders_lock);
 		clear_bit(order, &huge_anon_orders_always);
 		clear_bit(order, &huge_anon_orders_inherit);
 		clear_bit(order, &huge_anon_orders_madvise);
-		spin_unlock(&huge_anon_orders_lock);
 	} else
 		ret = -EINVAL;
+	spin_unlock(&huge_anon_orders_lock);

 	return ret;
 }
-- 
2.15.2

Re: [PATCH linux-next] mm/huge_memory: remove redundant locking when parsing THP sysfs input

[Matthew Wilcox]

On Sat, May 11, 2024 at 02:40:48PM +0800, xu.xin16@zte.com.cn wrote:
> From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> 
> Since sysfs_streq() only performs a simple memory comparison operation
> and will not introduce any sleepable operation, So there is no
> need to drop the lock when parsing input. Remove redundant lock
> and unlock operations to make code cleaner.

i disagree that it makes the code cleaner.

Re: [PATCH linux-next] mm/huge_memory: remove redundant locking when parsing THP sysfs input

[Andrew Morton]

(cc Muchun)

On Sat, 11 May 2024 17:05:13 +0100 Matthew Wilcox <willy@infradead.org> wrote:

> On Sat, May 11, 2024 at 02:40:48PM +0800, xu.xin16@zte.com.cn wrote:
> > From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> > 
> > Since sysfs_streq() only performs a simple memory comparison operation
> > and will not introduce any sleepable operation, So there is no
> > need to drop the lock when parsing input. Remove redundant lock
> > and unlock operations to make code cleaner.
> 
> i disagree that it makes the code cleaner.

Oh.  Why is that?  The end result looks nice to me and saves a bit of
.text.

Re: [PATCH linux-next] mm/huge_memory: remove redundant locking when parsing THP sysfs input

[David Hildenbrand]

On 11.05.24 08:40, xu.xin16@zte.com.cn wrote:
> From: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> 
> Since sysfs_streq() only performs a simple memory comparison operation
> and will not introduce any sleepable operation, So there is no
> need to drop the lock when parsing input. Remove redundant lock
> and unlock operations to make code cleaner.
> 
> Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> ---
>   mm/huge_memory.c | 10 ++--------
>   1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 89f58c7603b2..87123a87cb21 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -478,32 +478,26 @@ static ssize_t thpsize_enabled_store(struct kobject *kobj,
>   	int order = to_thpsize(kobj)->order;
>   	ssize_t ret = count;
> 
> +	spin_lock(&huge_anon_orders_lock);
>   	if (sysfs_streq(buf, "always")) {
> -		spin_lock(&huge_anon_orders_lock);
>   		clear_bit(order, &huge_anon_orders_inherit);
>   		clear_bit(order, &huge_anon_orders_madvise);
>   		set_bit(order, &huge_anon_orders_always);
> -		spin_unlock(&huge_anon_orders_lock);
>   	} else if (sysfs_streq(buf, "inherit")) {
> -		spin_lock(&huge_anon_orders_lock);
>   		clear_bit(order, &huge_anon_orders_always);
>   		clear_bit(order, &huge_anon_orders_madvise);
>   		set_bit(order, &huge_anon_orders_inherit);
> -		spin_unlock(&huge_anon_orders_lock);
>   	} else if (sysfs_streq(buf, "madvise")) {
> -		spin_lock(&huge_anon_orders_lock);
>   		clear_bit(order, &huge_anon_orders_always);
>   		clear_bit(order, &huge_anon_orders_inherit);
>   		set_bit(order, &huge_anon_orders_madvise);
> -		spin_unlock(&huge_anon_orders_lock);
>   	} else if (sysfs_streq(buf, "never")) {
> -		spin_lock(&huge_anon_orders_lock);
>   		clear_bit(order, &huge_anon_orders_always);
>   		clear_bit(order, &huge_anon_orders_inherit);
>   		clear_bit(order, &huge_anon_orders_madvise);
> -		spin_unlock(&huge_anon_orders_lock);
>   	} else
>   		ret = -EINVAL;
> +	spin_unlock(&huge_anon_orders_lock);
> 
>   	return ret;
>   }

No strong opinion

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb