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Subject: Re: [PATCH v2] f2fs: add bug_on when f2fs_gc even fails to get one
 victim
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     Chao Yu <yuchao0@huawei.com>, <chao@kernel.org>,
        <yunlong.song@icloud.com>, <miaoxie@huawei.com>,
        <bintian.wang@huawei.com>, <linux-fsdevel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>
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From:   Yunlong Song <yunlong.song@huawei.com>
Message-ID: <67f53739-ccc5-59be-9770-85d3ab76ed07@huawei.com>
Date:   Fri, 10 Nov 2017 10:11:15 +0800
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Agree.

On 2017/11/10 1:59, Jaegeuk Kim wrote:
> On 11/08, Yunlong Song wrote:
>> So we should use f2fs_bug_on(sbi, !total_freed && !sync && gc_type ==
>> FG_GC);
> f2fs_bug_on(sbi, !total_freed && has_not_enough_free_secs(sbi, 0, 0)); ?
>
>> On 2017/11/7 14:56, Chao Yu wrote:
>>> On 2017/11/7 12:01, Yunlong Song wrote:
>>>> 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);
>>> ioctl(F2FS_IOC_GARBAGE_COLLECT, &1) will simply trigger this bug_on, so we
>>> have to check the conditon only when we run out-of-free-space?
>>>
>>> Thanks,
>>>
>>>>>> 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
>>
> .
>

-- 
Thanks,
Yunlong Song


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