Sorry, misunderstanding, because I think when sync == true, FG_GC does not
check has_not_enough_free_secs, so maybe it does not have to do any gc 
at all.
For example, if there are 100 segments for f2fs, and 20 segments are full or
valid blocks over fggc_threshold, then it is correct to fail in get victim.


On 2017/11/7 11:26, Jaegeuk Kim wrote:
> On 11/07, Yunlong Song wrote:
>> Because I find that some out-of-free problem is caused by the failure
>> of get victim target. For example, chao has pointed out that he has
>> found out a bug when adding this bug_on last week.
> That's NOT what I asked. Why not checking FG_GC all the time like this?
>
> f2fs_bug_on(sbi, !total_freed && gc_type == FG_GC);
>
>> On 2017/11/7 10:40, Jaegeuk Kim wrote:
>>> On 11/06, Jaegeuk Kim wrote:
>>>> On 11/06, Yunlong Song wrote:
>>>>> Agree.
>>>>>
>>>>> On 2017/11/3 11:44, Jaegeuk Kim wrote:
>>>>>> On 10/13, Yunlong Song wrote:
>>>>>>> This can help us to debug on some corner case.
>>>>>>>
>>>>>>> Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
>>>>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>>>>> ---
>>>>>>>     fs/f2fs/gc.c | 6 +++++-
>>>>>>>     1 file changed, 5 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>>>>> index 197ebf4..2b03202 100644
>>>>>>> --- a/fs/f2fs/gc.c
>>>>>>> +++ b/fs/f2fs/gc.c
>>>>>>> @@ -986,6 +986,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>>>>>>     		.ilist = LIST_HEAD_INIT(gc_list.ilist),
>>>>>>>     		.iroot = RADIX_TREE_INIT(GFP_NOFS),
>>>>>>>     	};
>>>>>>> +	bool need_fggc = false;
>>>>>>>     	trace_f2fs_gc_begin(sbi->sb, sync, background,
>>>>>>>     				get_pages(sbi, F2FS_DIRTY_NODES),
>>>>>>> @@ -1018,8 +1019,10 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>>>>>>     			if (ret)
>>>>>>>     				goto stop;
>>>>>>>     		}
>>>>>>> -		if (has_not_enough_free_secs(sbi, 0, 0))
>>>>>>> +		if (has_not_enough_free_secs(sbi, 0, 0)) {
>>>>>>>     			gc_type = FG_GC;
>>>>>>> +			need_fggc = true;
>>>>>>> +		}
>>>>>>>     	}
>>>>>>>     	/* f2fs_balance_fs doesn't need to do BG_GC in critical path. */
>>>>>>> @@ -1028,6 +1031,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>>>>>>     		goto stop;
>>>>>>>     	}
>>>>>>>     	if (!__get_victim(sbi, &segno, gc_type)) {
>>>>>>> +		f2fs_bug_on(sbi, !total_freed && need_fggc);
>>>>>> Just like this?
>>>>> That's OK.
>>>> I'm not quite sure whether this is really a bug_on case.
>>>> Let me make it WARN_ON() for debugging purpose first.
>>> BTW, why is this the special case where BG_GC detects FG_GC?
>>>
>>>> Thanks,
>>>>
>>>>>> 		f2fs_bug_on(sbi, !total_freed && !sync && gc_type == FG_GC);
>>>>>>
>>>>>>>     		ret = -ENODATA;
>>>>>>>     		goto stop;
>>>>>>>     	}
>>>>>>> -- 
>>>>>>> 1.8.5.2
>>>>>> .
>>>>>>
>>>>> -- 
>>>>> Thanks,
>>>>> Yunlong Song
>>>>>
>>> .
>>>
>> -- 
>> Thanks,
>> Yunlong Song
>>
> .
>

-- 
Thanks,
Yunlong Song