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

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Message-ID: <20181016031052.GA19956@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Mon, 15 Oct 2018 20:10:52 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
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 10/16, Chao Yu wrote:
> 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:

Well, wait_on_stable_page() doesn't guarantee its end_io. So, I'm not sure
this is the only case.

> 
> 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);
> >>>
> > 
> > .
> >