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Date:   Wed, 27 May 2020 10:35:35 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <kernel-team@...roid.com>, <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: avoid inifinite loop to wait for
 flushing node pages at cp_error

On 2020/5/26 9:56, Jaegeuk Kim wrote:
> On 05/26, Chao Yu wrote:
>> On 2020/5/26 9:11, Chao Yu wrote:
>>> On 2020/5/25 23:06, Jaegeuk Kim wrote:
>>>> On 05/25, Chao Yu wrote:
>>>>> On 2020/5/25 11:56, Jaegeuk Kim wrote:
>>>>>> Shutdown test is somtimes hung, since it keeps trying to flush dirty node pages

    71.07%     0.01%  kworker/u256:1+  [kernel.kallsyms]  [k] wb_writeback
            |
             --71.06%--wb_writeback
                       |
                       |--68.96%--__writeback_inodes_wb
                       |          |
                       |           --68.95%--writeback_sb_inodes
                       |                     |
                       |                     |--65.08%--__writeback_single_inode
                       |                     |          |
                       |                     |           --64.35%--do_writepages
                       |                     |                     |
                       |                     |                     |--59.83%--f2fs_write_node_pages
                       |                     |                     |          |
                       |                     |                     |           --59.74%--f2fs_sync_node_pages
                       |                     |                     |                     |
                       |                     |                     |                     |--27.91%--pagevec_lookup_range_tag
                       |                     |                     |                     |          |
                       |                     |                     |                     |           --27.90%--find_get_pages_range_tag

Before umount, kworker will always hold one core, that looks not reasonable,
to avoid that, could we just allow node write, since it's out-place-update,
and cp is not allowed, we don't need to worry about its effect on data on
previous checkpoint, and it can decrease memory footprint cost by node pages.

Thanks,

>>>>>
>>>>> IMO, for umount case, we should drop dirty reference and dirty pages on meta/data
>>>>> pages like we change for node pages to avoid potential dead loop...
>>>>
>>>> I believe we're doing for them. :P
>>>
>>> Actually, I mean do we need to drop dirty meta/data pages explicitly as below:
>>>
>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>> index 3dc3ac6fe143..4c08fd0a680a 100644
>>> --- a/fs/f2fs/checkpoint.c
>>> +++ b/fs/f2fs/checkpoint.c
>>> @@ -299,8 +299,15 @@ static int __f2fs_write_meta_page(struct page *page,
>>>
>>>  	trace_f2fs_writepage(page, META);
>>>
>>> -	if (unlikely(f2fs_cp_error(sbi)))
>>> +	if (unlikely(f2fs_cp_error(sbi))) {
>>> +		if (is_sbi_flag_set(sbi, SBI_IS_CLOSE)) {
>>> +			ClearPageUptodate(page);
>>> +			dec_page_count(sbi, F2FS_DIRTY_META);
>>> +			unlock_page(page);
>>> +			return 0;
>>> +		}
>>>  		goto redirty_out;
>>> +	}
>>>  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
>>>  		goto redirty_out;
>>>  	if (wbc->for_reclaim && page->index < GET_SUM_BLOCK(sbi, 0))
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 48a622b95b76..94b342802513 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -2682,6 +2682,12 @@ int f2fs_write_single_data_page(struct page *page, int *submitted,
>>>
>>>  	/* we should bypass data pages to proceed the kworkder jobs */
>>>  	if (unlikely(f2fs_cp_error(sbi))) {
>>> +		if (is_sbi_flag_set(sbi, SBI_IS_CLOSE)) {
>>> +			ClearPageUptodate(page);
>>> +			inode_dec_dirty_pages(inode);
>>> +			unlock_page(page);
>>> +			return 0;
>>> +		}
>>
>> Oh, I notice previously, we will drop non-directory inode's dirty pages directly,
>> however, during umount, we'd better drop directory inode's dirty pages as well, right?
> 
> Hmm, I remember I dropped them before. Need to double check.
> 
>>
>>>  		mapping_set_error(page->mapping, -EIO);
>>>  		/*
>>>  		 * don't drop any dirty dentry pages for keeping lastest
>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>>> in an inifinite loop. Let's drop dirty pages at umount in that case.
>>>>>>
>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>>>>> ---
>>>>>> v3:
>>>>>>  - fix wrong unlock
>>>>>>
>>>>>> v2:
>>>>>>  - fix typos
>>>>>>
>>>>>>  fs/f2fs/node.c | 9 ++++++++-
>>>>>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
>>>>>> index e632de10aedab..e0bb0f7e0506e 100644
>>>>>> --- a/fs/f2fs/node.c
>>>>>> +++ b/fs/f2fs/node.c
>>>>>> @@ -1520,8 +1520,15 @@ static int __write_node_page(struct page *page, bool atomic, bool *submitted,
>>>>>>  
>>>>>>  	trace_f2fs_writepage(page, NODE);
>>>>>>  
>>>>>> -	if (unlikely(f2fs_cp_error(sbi)))
>>>>>> +	if (unlikely(f2fs_cp_error(sbi))) {
>>>>>> +		if (is_sbi_flag_set(sbi, SBI_IS_CLOSE)) {
>>>>>> +			ClearPageUptodate(page);
>>>>>> +			dec_page_count(sbi, F2FS_DIRTY_NODES);
>>>>>> +			unlock_page(page);
>>>>>> +			return 0;
>>>>>> +		}
>>>>>>  		goto redirty_out;
>>>>>> +	}
>>>>>>  
>>>>>>  	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
>>>>>>  		goto redirty_out;
>>>>>>
>>>> .
>>>>
>>>
>>>
>>> _______________________________________________
>>> Linux-f2fs-devel mailing list
>>> Linux-f2fs-devel@...ts.sourceforge.net
>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>> .
>>>
> .
> 

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