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Subject: Re: [f2fs-dev] [PATCH] f2fs: don't skip writeback of quota data
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>, <kernel-team@android.com>
References: <20200709053027.351974-1-jaegeuk@kernel.org>
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 <ae1a3e8a-6209-8d4b-7235-5c8897076501@huawei.com>
 <20200710032616.GC545837@google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <01d0db54-eee1-f6cd-76c3-ebe59a7abae4@huawei.com>
Date:   Fri, 10 Jul 2020 11:41:31 +0800
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On 2020/7/10 11:26, Jaegeuk Kim wrote:
> 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.

Okay,

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

Did you record any callstack after the issue happened?

Still I'm confused that why directory's data written could be skipped, but
quota's data couldn't, what's the difference?

> 
>>
>> Thanks,
>>
>>>
>>> Thanks,
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.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))
>>>>>
>>> .
>>>
> .
>