Re: [PATCH 1/2] f2fs: fix to commit bio cache after flushing node pages

[Chao Yu <yuchao0@huawei.com>]

Hi Jaegeuk,

On 2016/9/27 2:33, Jaegeuk Kim wrote:
> Hi Chao,
> 
> On Tue, Sep 27, 2016 at 12:09:52AM +0800, Chao Yu wrote:
>> From: Chao Yu <yuchao0@huawei.com>
>>
>> In sync_node_pages, we won't check and commit last merged pages in private
>> bio cache of f2fs, as these pages were taged as writeback, someone who is
>> waiting for writebacking of the page will be blocked until the cache was
>> committed by someone else.
>>
>> We need to commit node type bio cache to avoid potential deadlock or long
>> delay of waiting writeback.
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>>  fs/f2fs/node.c | 11 +++++++++--
>>  1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
>> index 9faddcd..f73f774 100644
>> --- a/fs/f2fs/node.c
>> +++ b/fs/f2fs/node.c
>> @@ -1416,6 +1416,7 @@ int sync_node_pages(struct f2fs_sb_info *sbi, struct writeback_control *wbc)
>>  	struct pagevec pvec;
>>  	int step = 0;
>>  	int nwritten = 0;
>> +	int ret = 0;
>>  
>>  	pagevec_init(&pvec, 0);
>>  
>> @@ -1436,7 +1437,8 @@ next_step:
>>  
>>  			if (unlikely(f2fs_cp_error(sbi))) {
>>  				pagevec_release(&pvec);
>> -				return -EIO;
>> +				ret = -EIO;
>> +				goto out;
>>  			}
>>  
>>  			/*
>> @@ -1487,6 +1489,8 @@ continue_unlock:
>>  
>>  			if (NODE_MAPPING(sbi)->a_ops->writepage(page, wbc))
>>  				unlock_page(page);
>> +			else
>> +				nwritten++;
>>  
>>  			if (--wbc->nr_to_write == 0)
>>  				break;
>> @@ -1504,7 +1508,10 @@ continue_unlock:
>>  		step++;
>>  		goto next_step;
>>  	}
>> -	return nwritten;
>> +out:
>> +	if (nwritten)
>> +		f2fs_submit_merged_bio(sbi, NODE, WRITE);
> 
> IIRC, we don't need to flush this, since f2fs_submit_merged_bio_cond() would
> handle this in f2fs_wait_on_page_writeback().

Yes, it covers all the cases in f2fs private codes, but there are still some
codes in mm or fs directory, and they didn't use f2fs_wait_on_page_writeback
when waiting page writeback. Such as do_writepages && filemap_fdatawait in
__writeback_single_inode...

Thanks,

> 
> Thanks,
> 
>> +	return ret;
>>  }
>>  
>>  int wait_on_node_pages_writeback(struct f2fs_sb_info *sbi, nid_t ino)
>> -- 
>> 2.7.2
> 
> .
>