2024-05-11 06:41:51

by xu.xin16

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

From: Ran Xiaokai <[email protected]>

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 <[email protected]>
---
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

2024-05-11 16:05:27

by Matthew Wilcox

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

On Sat, May 11, 2024 at 02:40:48PM +0800, [email protected] wrote:
> From: Ran Xiaokai <[email protected]>
>
> 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.

2024-05-11 21:35:12

by Andrew Morton

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

(cc Muchun)

On Sat, 11 May 2024 17:05:13 +0100 Matthew Wilcox <[email protected]> wrote:

> On Sat, May 11, 2024 at 02:40:48PM +0800, [email protected] wrote:
> > From: Ran Xiaokai <[email protected]>
> >
> > 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.

2024-05-13 15:59:43

by David Hildenbrand

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

On 11.05.24 08:40, [email protected] wrote:
> From: Ran Xiaokai <[email protected]>
>
> 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 <[email protected]>
> ---
> 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 <[email protected]>

--
Cheers,

David / dhildenb