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Subject: Re: [PATCH v2] f2fs: add bug_on when f2fs_gc even fails to get one
 victim
To:     Chao Yu <yuchao0@huawei.com>, Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <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: <19eec8fd-e941-770a-9477-6ad2d266d475@huawei.com>
Date:   Wed, 8 Nov 2017 11:06:29 +0800
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So we should use f2fs_bug_on(sbi, !total_freed && !sync && gc_type == 
FG_GC);

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


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