linux-kernel - Re: [f2fs-dev] [PATCH 1/2] f2fs: wait on atomic writes to count F2FS_CP_WB

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Date:   Fri, 4 Jan 2019 12:36:04 -0800
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, stable@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: wait on atomic writes to count
 F2FS_CP_WB_DATA

On 01/04, Chao Yu wrote:
> On 2019/1/4 12:20, Jaegeuk Kim wrote:
> > Otherwise, we can get wrong counts incurring checkpoint hang.
> > 
> > IO_W (CP:  -24, Data:   24, Flush: (   0    0    1), Discard: (   0    0))
> > 
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> 
> Good catch! ;)
> 
> I can understand this condition, but for other new developer who reads this
> commit, it will be a little hard to understand situation here.
> 
> How about explaining a little more about problem here, maybe:
> 
> Thread A			Thread B		
> - f2fs_write_data_pages
>  -  __write_data_page
>   - f2fs_submit_page_write
>    - inc_page_count(F2FS_WB_DATA)
>      type is F2FS_WB_DATA due to file is non-atomic one
> - f2fs_ioc_start_atomic_write
>  - set_inode_flag(FI_ATOMIC_FILE)
> 				- f2fs_write_end_io
> 				 - dec_page_count(F2FS_WB_CP_DATA)
> 				   type is F2FS_WB_DATA due to file becomes
> 				   atomic one
> 
> Reviewed-by: Chao Yu <yuchao0@...wei.com>

Thanks, added the comment. :P

> 
> Thanks,
>