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 17:31:52 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
CC:     <stable@...r.kernel.org>
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: wait on atomic writes to count
 F2FS_CP_WB_DATA

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,