Re: [PATCH 1/2] f2fs: enable to gc page whose inode already atomic commit

[Chao Yu <yuchao0@huawei.com>]

On 2018/2/5 17:37, Yunlong Song wrote:
> 
>> OK, details as I explained before:
>>
>> atomic_commit				GC
>> - file_write_and_wait_range
>> 					- move_data_block
>> 					 - f2fs_submit_page_write
>> 					  - f2fs_update_data_blkaddr
>> 					   - set_page_dirty
>>   - fsync_node_pages
>>
>> 1. atomic writes data page #1 & update node #1
>> 2. GC data page #2 & update node #2
>> 3. page #1 & node #1 & #2 can be committed into nand flash before page #2 be
>> committed.
>>
>> After a sudden pow-cut, database transaction will be inconsistent. So I think
>> there will be better to exclude gc/atomic_write to each other, with a lock
>> instead of flag checking.
>>
> 
> I do not understand why this transaction is inconsistent, is it a
> problem that page #2 is not committed into nand flash? Since normal

Yes, node #2 contains newly updated LBAx of page #2, but if page #2 is not
committed to LBAx, after recovery, page #2 's block address in node #2 will
point to LBAx which contains random data, result in corrupted db file.

> gc also has this problem:
> 
> Suppose that there is db file A, f2fs_gc moves data page #1 of db file
> A. But if write checkpoint only commit node page #1 and then a sudden

f2fs will ensure GCed data being persisted during checkpoint, so migrated page
#1 and updated node #1 will both be committed in this checkpoint.

Please check WB_DATA_TYPE macro to see how we define data type that cp
guarantees to writeback.

> power-cut happens. Data page #1 is not committed to nand flash, but
> node page #1 is committed. Is the db transaction broken and
> inconsistent?
> 
> Come back to your example, I think data page 2 of atomic file does not
> belong to this transaction, so even node page 2 is committed, it is just

If node #2 is committed only, it will be harmful to db transaction due to the
reason I said above.

Thanks,

> the same problem as what I have listed above(db file A), and it does not
> break this transaction.
> 
>> Thanks,
>>
>>>>>>
>>>>>> So how about just using dio_rwsem[WRITE] during atomic committing to exclude
>>>>>> GCing data block of atomic opened file?
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>>
>>>>>>> Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
>>>>>>> ---
>>>>>>>     fs/f2fs/data.c | 5 ++---
>>>>>>>     fs/f2fs/gc.c   | 6 ++++--
>>>>>>>     2 files changed, 6 insertions(+), 5 deletions(-)
>>>>>>>
>>>>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>>>>> index 7435830..edafcb6 100644
>>>>>>> --- a/fs/f2fs/data.c
>>>>>>> +++ b/fs/f2fs/data.c
>>>>>>> @@ -1580,14 +1580,13 @@ bool should_update_outplace(struct inode *inode, struct f2fs_io_info *fio)
>>>>>>>     		return true;
>>>>>>>     	if (S_ISDIR(inode->i_mode))
>>>>>>>     		return true;
>>>>>>> -	if (f2fs_is_atomic_file(inode))
>>>>>>> -		return true;
>>>>>>>     	if (fio) {
>>>>>>>     		if (is_cold_data(fio->page))
>>>>>>>     			return true;
>>>>>>>     		if (IS_ATOMIC_WRITTEN_PAGE(fio->page))
>>>>>>>     			return true;
>>>>>>> -	}
>>>>>>> +	} else if (f2fs_is_atomic_file(inode))
>>>>>>> +		return true;
>>>>>>>     	return false;
>>>>>>>     }
>>>>>>>     
>>>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>>>>> index b9d93fd..84ab3ff 100644
>>>>>>> --- a/fs/f2fs/gc.c
>>>>>>> +++ b/fs/f2fs/gc.c
>>>>>>> @@ -622,7 +622,8 @@ static void move_data_block(struct inode *inode, block_t bidx,
>>>>>>>     	if (!check_valid_map(F2FS_I_SB(inode), segno, off))
>>>>>>>     		goto out;
>>>>>>>     
>>>>>>> -	if (f2fs_is_atomic_file(inode))
>>>>>>> +	if (f2fs_is_atomic_file(inode) &&
>>>>>>> +		!f2fs_is_commit_atomic_write(inode))
>>>>>>>     		goto out;
>>>>>>>     
>>>>>>>     	if (f2fs_is_pinned_file(inode)) {
>>>>>>> @@ -729,7 +730,8 @@ static void move_data_page(struct inode *inode, block_t bidx, int gc_type,
>>>>>>>     	if (!check_valid_map(F2FS_I_SB(inode), segno, off))
>>>>>>>     		goto out;
>>>>>>>     
>>>>>>> -	if (f2fs_is_atomic_file(inode))
>>>>>>> +	if (f2fs_is_atomic_file(inode) &&
>>>>>>> +		!f2fs_is_commit_atomic_write(inode))
>>>>>>>     		goto out;
>>>>>>>     	if (f2fs_is_pinned_file(inode)) {
>>>>>>>     		if (gc_type == FG_GC)
>>>>>>>
>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>
>>>>
>>>> .
>>>>
>>>
>>
>>
>> .
>>
>