linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: clear cold data flag if IO is not counted

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Date:   Tue, 16 Oct 2018 09:31:25 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH] f2fs: clear cold data flag if IO is not
 counted

On 2018/10/16 7:08, Jaegeuk Kim wrote:
> On 10/15, Chao Yu wrote:
>> On 2018/10/11 5:22, Jaegeuk Kim wrote:
>>> If we clear the cold data flag out of the writeback flow, we can miscount
>>> -1 by end_io.
>>
>> I didn't get it, which count do you mean?
> 
> It's the number of dirty pages.
> 
> Balancing F2FS Async:
>   - IO (CP:    1, Data:   -1, Flush: (   0    0    1), Discard: (   0 129304)) cmd:    0 undiscard:   0
> 

So I guess the race should be:

GC thread:				IRQ
- move_data_page()
 - set_page_dirty()
  - clear_cold_data()
					- f2fs_write_end_io()
					 - type = WB_DATA_TYPE(page);
					   here, we get wrong type
					 - dec_page_count(sbi, type);
 - f2fs_wait_on_page_writeback()

How about relocate wait_writeback & set_page_dirty to avoid above race:

move_data_page()

retry:
		f2fs_wait_on_page_writeback(page, DATA, true);
		set_page_dirty(page);

Thanks,

>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>>  fs/f2fs/data.c | 4 ----
>>>  1 file changed, 4 deletions(-)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 29a9d3b8f709..4102799b5558 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -2636,10 +2636,6 @@ static int f2fs_set_data_page_dirty(struct page *page)
>>>  	if (!PageUptodate(page))
>>>  		SetPageUptodate(page);
>>>  
>>> -	/* don't remain PG_checked flag which was set during GC */
>>> -	if (is_cold_data(page))
>>> -		clear_cold_data(page);
>>> -
>>>  	if (f2fs_is_atomic_file(inode) && !f2fs_is_commit_atomic_write(inode)) {
>>>  		if (!IS_ATOMIC_WRITTEN_PAGE(page)) {
>>>  			f2fs_register_inmem_page(inode, page);
>>>
> 
> .
>