[PATCH 1/2] f2fs: reorganize f2fs_vm_page_mkwrite

[PATCH 1/2] f2fs: reorganize f2fs_vm_page_mkwrite

[Namjae Jeon]

From: Namjae Jeon <namjae.jeon@samsung.com>

Few things can be changed in the default mkwrite function
1) Make file_update_time at the start before acquiring any lock
2) the condition page_offset(page) >= i_size_read(inode) should be
 changed to page_offset(page) > i_size_read
3) Move wait_on_page_writeback.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
---
 fs/f2fs/file.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 5cc4dd8..dc76f9b 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -63,9 +63,10 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
 	f2fs_put_dnode(&dn);
 	mutex_unlock_op(sbi, ilock);
 
+	file_update_time(vma->vm_file);
 	lock_page(page);
 	if (page->mapping != inode->i_mapping ||
-			page_offset(page) >= i_size_read(inode) ||
+			page_offset(page) > i_size_read(inode) ||
 			!PageUptodate(page)) {
 		unlock_page(page);
 		err = -EFAULT;
@@ -76,10 +77,7 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
 	 * check to see if the page is mapped already (no holes)
 	 */
 	if (PageMappedToDisk(page))
-		goto out;
-
-	/* fill the page */
-	wait_on_page_writeback(page);
+		goto mapped;
 
 	/* page is wholly or partially inside EOF */
 	if (((page->index + 1) << PAGE_CACHE_SHIFT) > i_size_read(inode)) {
@@ -90,7 +88,9 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
 	set_page_dirty(page);
 	SetPageUptodate(page);
 
-	file_update_time(vma->vm_file);
+mapped:
+	/* fill the page */
+	wait_on_page_writeback(page);
 out:
 	sb_end_pagefault(inode->i_sb);
 	return block_page_mkwrite_return(err);
-- 
1.7.9.5

Re: [PATCH 1/2] f2fs: reorganize f2fs_vm_page_mkwrite

[Jaegeuk Kim]

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Hi,

2013-04-28 (일), 09:04 +0900, Namjae Jeon:
> From: Namjae Jeon <namjae.jeon@samsung.com>
> 
> Few things can be changed in the default mkwrite function
> 1) Make file_update_time at the start before acquiring any lock
> 2) the condition page_offset(page) >= i_size_read(inode) should be
>  changed to page_offset(page) > i_size_read
> 3) Move wait_on_page_writeback.
> 
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
> ---
>  fs/f2fs/file.c |   12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 5cc4dd8..dc76f9b 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -63,9 +63,10 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
>  	f2fs_put_dnode(&dn);
>  	mutex_unlock_op(sbi, ilock);
>  
> +	file_update_time(vma->vm_file);

Should we update time even if error is occurred below?

>  	lock_page(page);
>  	if (page->mapping != inode->i_mapping ||
> -			page_offset(page) >= i_size_read(inode) ||
> +			page_offset(page) > i_size_read(inode) ||

Why? IMO, there was no problem.

>  			!PageUptodate(page)) {
>  		unlock_page(page);
>  		err = -EFAULT;
> @@ -76,10 +77,7 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
>  	 * check to see if the page is mapped already (no holes)
>  	 */
>  	if (PageMappedToDisk(page))
> -		goto out;
> -
> -	/* fill the page */
> -	wait_on_page_writeback(page);
> +		goto mapped;
>  
>  	/* page is wholly or partially inside EOF */
>  	if (((page->index + 1) << PAGE_CACHE_SHIFT) > i_size_read(inode)) {
> @@ -90,7 +88,9 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct *vma,
>  	set_page_dirty(page);
>  	SetPageUptodate(page);
>  
> -	file_update_time(vma->vm_file);
> +mapped:
> +	/* fill the page */
> +	wait_on_page_writeback(page);
>  out:
>  	sb_end_pagefault(inode->i_sb);
>  	return block_page_mkwrite_return(err);

-- 
Jaegeuk Kim
Samsung

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Re: [PATCH 1/2] f2fs: reorganize f2fs_vm_page_mkwrite

[Namjae Jeon]

2013/4/29, Jaegeuk Kim <jaegeuk.kim@samsung.com>:
> Hi,
Hi. Jaegeuk.
>
> 2013-04-28 (일), 09:04 +0900, Namjae Jeon:
>> From: Namjae Jeon <namjae.jeon@samsung.com>
>>
>> Few things can be changed in the default mkwrite function
>> 1) Make file_update_time at the start before acquiring any lock
>> 2) the condition page_offset(page) >= i_size_read(inode) should be
>>  changed to page_offset(page) > i_size_read
>> 3) Move wait_on_page_writeback.
>>
>> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
>> Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
>> ---
>>  fs/f2fs/file.c |   12 ++++++------
>>  1 file changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 5cc4dd8..dc76f9b 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -63,9 +63,10 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct
>> *vma,
>>  	f2fs_put_dnode(&dn);
>>  	mutex_unlock_op(sbi, ilock);
>>
>> +	file_update_time(vma->vm_file);
>
> Should we update time even if error is occurred below?
Should we update time even if error is occurred below?
Even though the original time change position regarding
file_update_time is correct with respect to the failure conditions,
but we referred the code in other file systems.
We found that file_update_time in page fault is not critical part, so
first thing is to move this out of the locking.
We can see the following comment in block_page_mkwrite.
/*
	 * Update file times before taking page lock. We may end up failing the
	 * fault so this update may be superfluous but who really cares...
	 */
	
Most filesystems use it regardless of below condition. Ext4 also does
this at the beginning of mkwrite-> just after
sb_start_pagefault(inode->i_sb);
>
>>  	lock_page(page);
>>  	if (page->mapping != inode->i_mapping ||
>> -			page_offset(page) >= i_size_read(inode) ||
>> +			page_offset(page) > i_size_read(inode) ||
>
> Why? IMO, there was no problem.
There is no problem and we could not find a test case either, but
looking at the code we thought it could be an alignment issue if due
to index, the page_offset() and i_size_read() ? may cause some
boundary condition.
The above changes were introduced without citing any issues, but just
to align the code.
So we can ignore this changed line :)

Thanks~
>
>>  			!PageUptodate(page)) {
>>  		unlock_page(page);
>>  		err = -EFAULT;
>> @@ -76,10 +77,7 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct
>> *vma,
>>  	 * check to see if the page is mapped already (no holes)
>>  	 */
>>  	if (PageMappedToDisk(page))
>> -		goto out;
>> -
>> -	/* fill the page */
>> -	wait_on_page_writeback(page);
>> +		goto mapped;
>>
>>  	/* page is wholly or partially inside EOF */
>>  	if (((page->index + 1) << PAGE_CACHE_SHIFT) > i_size_read(inode)) {
>> @@ -90,7 +88,9 @@ static int f2fs_vm_page_mkwrite(struct vm_area_struct
>> *vma,
>>  	set_page_dirty(page);
>>  	SetPageUptodate(page);
>>
>> -	file_update_time(vma->vm_file);
>> +mapped:
>> +	/* fill the page */
>> +	wait_on_page_writeback(page);
>>  out:
>>  	sb_end_pagefault(inode->i_sb);
>>  	return block_page_mkwrite_return(err);
>
> --
> Jaegeuk Kim
> Samsung
>
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