[PATCH] sysfs/file: move NULL checks to where they make sense and can occur

[PATCH] sysfs/file: move NULL checks to where they make sense and can occur

[André Goddard Rosa]

... avoiding checking for NULL 2 times in a row when we already have a page.

It decreases code size:
text    data     bss     dec     hex filename
4246      48    4136    8430    20ee fs/sysfs/file-BEFORE.o
4214      48    4136    8398    20ce fs/sysfs/file-AFTER.o

Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>
---
 fs/sysfs/file.c |   16 +++++++++-------
 1 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index dc30d9e..962b190 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -79,10 +79,11 @@ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer
 	int ret = 0;
 	ssize_t count;
 
-	if (!buffer->page)
-		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
-	if (!buffer->page)
-		return -ENOMEM;
+	if (!buffer->page) {
+		buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
+		if (!buffer->page)
+			return -ENOMEM;
+	}
 
 	/* need attr_sd for attr and ops, its parent for kobj */
 	if (!sysfs_get_active_two(attr_sd))
@@ -167,10 +168,11 @@ fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t
 {
 	int error;
 
-	if (!buffer->page)
+	if (!buffer->page) {
 		buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
-	if (!buffer->page)
-		return -ENOMEM;
+		if (!buffer->page)
+			return -ENOMEM;
+	}
 
 	if (count >= PAGE_SIZE)
 		count = PAGE_SIZE - 1;
-- 
1.7.0.1.164.gbe2f

Re: [PATCH] sysfs/file: move NULL checks to where they make sense and can occur

[Tejun Heo]

Hello,

On 03/05/2010 07:46 PM, André Goddard Rosa wrote:
> ... avoiding checking for NULL 2 times in a row when we already have a page.
> 
> It decreases code size:
> text    data     bss     dec     hex filename
> 4246      48    4136    8430    20ee fs/sysfs/file-BEFORE.o
> 4214      48    4136    8398    20ce fs/sysfs/file-AFTER.o
> 
> Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>

Nacked-by: Tejun Heo <tj@kernel.org>

For this level of micro optimization to be meaningful, the code path
should be *really* *really* hot, which none of sysfs code pats are.
Whatever is easier to the eyes wins.

Thanks.

-- 
tejun

Re: [PATCH] sysfs/file: move NULL checks to where they make sense and can occur

[André Goddard Rosa]

Hello,

> On 03/05/2010 07:46 PM, André Goddard Rosa wrote:
>> ... avoiding checking for NULL 2 times in a row when we already have a page.
>>
>> It decreases code size:
>> text    data     bss     dec     hex filename
>> 4246      48    4136    8430    20ee fs/sysfs/file-BEFORE.o
>> 4214      48    4136    8398    20ce fs/sysfs/file-AFTER.o
>>
>> Signed-off-by: André Goddard Rosa <andre.goddard@gmail.com>
>
> Nacked-by: Tejun Heo <tj@kernel.org>
>
> For this level of micro optimization to be meaningful, the code path
> should be *really* *really* hot, which none of sysfs code pats are.
> Whatever is easier to the eyes wins.
>

    Ok Tejun, I understood your point of view.

Thanks,
André