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

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Date:   Fri, 17 Nov 2017 11:20:26 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Yunlong Song <yunlong.song@...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

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;
>>>>>
>>>> .
>>>>
>>
>> .
>>
>