linux-kernel - Re: [PATCH] f2fs: let f2fs also gc atomic file to avoid loop gc

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Date:   Fri, 17 Nov 2017 11:30:04 +0800
From:   Yunlong Song <yunlong.song@...wei.com>
To:     Chao Yu <yuchao0@...wei.com>, <jaegeuk@...nel.org>,
        <chao@...nel.org>, <yunlong.song@...oud.com>
CC:     <miaoxie@...wei.com>, <bintian.wang@...wei.com>,
        <linux-fsdevel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] f2fs: let f2fs also gc atomic file to avoid loop gc

How about add file_write_and_wait_range in __write_node_page as following:
if (atomic && !test_opt(sbi, NOBARRIER)) {
     file_write_and_wait_range(file, 0, LLONG_MAX);
     fio.op_flags |= REQ_PREFLUSH | REQ_FUA;
}

The all the GCed data will be flushed to non-volatile before last node 
write with REQ_PREFLUSH | REQ_FUA.

On 2017/11/17 11:20, Chao Yu wrote:
> On 2017/11/17 11:04, Yunlong Song wrote:
>> The atomic commit will trigger:
>>       -f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true)
>>           -file_write_and_wait_range(file, 0, LLONG_MAX)
>>           -fsync_node_pages
>>               -__write_node_page
>>                   -REQ_PREFLUSH | REQ_FUA
>>
>> So data is flushed to non-volatile before  last node write with > REQ_PREFLUSH | REQ_FUA,
> I mean GCed data.
>
> - file_write_and_wait_range
> 					- move_data_block
> 					 - f2fs_submit_page_write
> 					  - f2fs_update_data_blkaddr
> 					   - set_page_dirty
>   - fsync_node_pages
>
> Thanks,
>
>> we do not need to worry about the inconsistent problem. Right?
>>
>> On 2017/11/17 10:49, Chao Yu wrote:
>>> On 2017/11/17 8:58, Yunlong Song wrote:
>>>> Is there any problem if just deleting the judgement condition in this patch?
>>> IIRC, dirty node comes from data segment GC can be writebacked & flushed during
>>> atomic commit, but related data will still be in inner bio cache, after later
>>> SPOR, data would be inconsistent.
>>>
>>> Thanks,
>>>
>>>> On 2017/11/8 17:28, Chao Yu wrote:
>>>>> On 2017/11/8 10:34, Yunlong Song wrote:
>>>>>> If some files are opened with atomic flag and have not commited yet, at
>>>>>> the same time, if all the target victim segments have at least one page
>>>>>> of these atomic files, then f2fs gc will fail to do gc and hangs in the
>>>>>> process of go to gc_more, since gc_date_segment will not move any data
>>>>>> and get_valid_blocks will never be 0, then do_garbage_collect will
>>>>>> always return 0.
>>>>> Oh, I added this judgment condition to avoid ruining atomic write by data
>>>>> GC, could we find another way to solve this issue? BTW, if there is direct
>>>>> IO, we will also skip data segment GC.
>>>>>
>>>>> Thanks,
>>>>>
>>>>>> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
>>>>>> ---
>>>>>>     fs/f2fs/gc.c | 6 ------
>>>>>>     1 file changed, 6 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>>>> index 5d5bba4..3fdcd04 100644
>>>>>> --- a/fs/f2fs/gc.c
>>>>>> +++ b/fs/f2fs/gc.c
>>>>>> @@ -621,9 +621,6 @@ 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))
>>>>>> -		goto out;
>>>>>> -
>>>>>>     	set_new_dnode(&dn, inode, NULL, NULL, 0);
>>>>>>     	err = get_dnode_of_data(&dn, bidx, LOOKUP_NODE);
>>>>>>     	if (err)
>>>>>> @@ -718,9 +715,6 @@ 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))
>>>>>> -		goto out;
>>>>>> -
>>>>>>     	if (gc_type == BG_GC) {
>>>>>>     		if (PageWriteback(page))
>>>>>>     			goto out;
>>>>>>
>>>>> .
>>>>>
>>> .
>>>
>
> .
>

-- 
Thanks,
Yunlong Song