linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: don't skip writeback of quota data

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Message-ID: <20200710032616.GC545837@google.com>
Date:   Thu, 9 Jul 2020 20:26:16 -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, kernel-team@...roid.com
Subject: Re: [f2fs-dev] [PATCH] f2fs: don't skip writeback of quota data

On 07/10, Chao Yu wrote:
> On 2020/7/10 3:05, Jaegeuk Kim wrote:
> > On 07/09, Chao Yu wrote:
> >> On 2020/7/9 13:30, Jaegeuk Kim wrote:
> >>> It doesn't need to bypass flushing quota data in background.
> >>
> >> The condition is used to flush quota data in batch to avoid random
> >> small-sized udpate, did you hit any problem here?
> > 
> > I suspect this causes fault injection test being stuck by waiting for inode
> > writeback completion. With this patch, it has been running w/o any issue so far.
> > I keep an eye on this.
> 
> Hmmm.. so that this patch may not fix the root cause, and it may hiding the
> issue deeper.
> 
> How about just keeping this patch in our private branch to let fault injection
> test not be stuck? until we find the root cause in upstream codes.

Well, I don't think this hides something. When the issue happens, I saw inodes
being stuck due to writeback while only quota has some dirty data. At that time,
there was no dirty data page from other inodes.

More specifically, I suspect __writeback_inodes_sb_nr() gives WB_SYNC_NONE and
waits for wb_wait_for_completion().

> 
> Thanks,
> 
> > 
> > Thanks,
> > 
> >>
> >> Thanks,
> >>
> >>>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> >>> ---
> >>>  fs/f2fs/data.c | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> >>> index 44645f4f914b6..72e8b50e588c1 100644
> >>> --- a/fs/f2fs/data.c
> >>> +++ b/fs/f2fs/data.c
> >>> @@ -3148,7 +3148,7 @@ static int __f2fs_write_data_pages(struct address_space *mapping,
> >>>  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
> >>>  		goto skip_write;
> >>>  
> >>> -	if ((S_ISDIR(inode->i_mode) || IS_NOQUOTA(inode)) &&
> >>> +	if (S_ISDIR(inode->i_mode) &&
> >>>  			wbc->sync_mode == WB_SYNC_NONE &&
> >>>  			get_dirty_pages(inode) < nr_pages_to_skip(sbi, DATA) &&
> >>>  			f2fs_available_free_memory(sbi, DIRTY_DENTS))
> >>>
> > .
> >