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Subject: Re: [PATCH v2] f2fs: add bug_on when f2fs_gc even fails to get one
 victim
To:     Yunlong Song <yunlong.song@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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 <20171107032636.GB92599@jaegeuk-macbookpro.roam.corp.google.com>
 <7433d584-b1e0-76e9-a6e4-8da1218dd71d@huawei.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <d036e6c2-af73-3781-242d-5d56a0933e8a@huawei.com>
Date:   Tue, 7 Nov 2017 14:56:26 +0800
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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
>>>
>> .
>>
> 


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