Re: [f2fs-dev] [PATCH v2] f2fs: add bug_on when f2fs_gc even fails to get one victim

[Yunlong Song <yunlong.song@huawei.com>]

So it seems it is really useful to add this bug_on in gc.

On 2017/10/31 11:17, Chao Yu wrote:
> On 2017/10/31 9:32, Yunlong Song wrote:
>> I think there may be bugs somewhere, since no victim is selected but it
>> really needs gc.
>> What is the size of the data image?
> I have providered the testcase, could you check that?
>
>>>>> I can hit this bugon with generic/015 of fstest easily, could have a look at
>>>>> this?
> Anyway, I have looked into this issue at last weekend, forgot to post related
> info. It shows that if the image size is very small, e.g. 50MB, current
> segment will encroach overprov and reserved segments, so free segment count will
> always be small than reserved segment threshold, result in triggering bugon in
> FGGC.
>
> [SB: 1] [CP: 2] [SIT: 2] [NAT: 2] [SSA: 1] [MAIN: 17(OverProv:14 Resv:12)]
>
>    - Valid: 6
>    - Dirty: 0
>    - Prefree: 0
>    - Free: 11 (11)
>
> I modify mkfs.f2fs forcedly as below, which could let generic/015 passed:
>
> diff --git a/mkfs/f2fs_format.c b/mkfs/f2fs_format.c
> index 8a821d3a1747..774bbef73d9a 100644
> --- a/mkfs/f2fs_format.c
> +++ b/mkfs/f2fs_format.c
> @@ -371,6 +371,12 @@ static int f2fs_prepare_super_block(void)
>   			(2 * (100 / c.overprovision + 1) + 6)
>   			* c.segs_per_sec;
>
> +	if (get_sb(segment_count_main) * (100 - c.overprovision) / 100 -
> +		c.reserved_segments < 6) {
> +		c.overprovision = 50;
> +		c.reserved_segments = get_sb(segment_count_main) - 6 * 2;
> +	}
> +
>   	uuid_generate(sb->uuid);
>
>   	/* precompute checksum seed for metadata */
>
> Thanks,
>
>> On 2017/10/16 11:25, Chao Yu wrote:
>>> On 2017/10/14 20:34, Yunlong Song wrote:
>>>> Do you mean check out-of-space test? I have tried that but no bugon.
>>> Yes, test recent f2fs codes with kernel 4.13.0-rc1+ in VM, FYI:
>>>
>>> kernel BUG at gc.c:1034!
>>> invalid opcode: 0000 [#1] SMP
>>> Hardware name: Xen HVM domU, BIOS 4.1.2_115-900.260_ 11/06/2015
>>> RIP: 0010:f2fs_gc+0x6e5/0x6f0 [f2fs]
>>> RSP: 0018:ffffc90004af7b40 EFLAGS: 00010202
>>> RAX: ffff8801b0a15940 RBX: 0000000000000000 RCX: 0000000000000000
>>> RDX: ffff8801b0a15940 RSI: ffff8801978d5f00 RDI: ffff880128148048
>>> RBP: ffffc90004af7c38 R08: ffff8801978d5f00 R09: 0000000000000003
>>> R10: 0000000000000003 R11: ffff8800060703a0 R12: 0000000000000000
>>> R13: 0000000000000000 R14: 0000000000000001 R15: ffff8801b4279800
>>> FS:  00007f23493cb740(0000) GS:ffff880216f00000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 00007ffd05402ff8 CR3: 00000001bffb3000 CR4: 00000000001406e0
>>> Call Trace:
>>>    f2fs_balance_fs+0x123/0x140 [f2fs]
>>>    f2fs_create+0x130/0x240 [f2fs]
>>>    path_openat+0xee7/0x1360
>>>    do_filp_open+0x7e/0xd0
>>>    do_sys_open+0x115/0x1f0
>>>    SyS_open+0x1e/0x20
>>>    do_syscall_64+0x6e/0x160
>>>    entry_SYSCALL64_slow_path+0x25/0x25
>>>
>>> Thanks,
>>>
>>>> On 2017/10/14 8:17, Chao Yu wrote:
>>>>> On 2017/10/13 21:31, Yunlong Song wrote:
>>>>>> This can help us to debug on some corner case.
>>>>> I can hit this bugon with generic/015 of fstest easily, could have a look at
>>>>> this?
>>>>>
>>>>> Thanks,
>>>>>
>>>>>> 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);
>>>>>>     		ret = -ENODATA;
>>>>>>     		goto stop;
>>>>>>     	}
>>>>>>
>>>>> .
>>>>>
>>> .
>>>
>
> .
>

-- 
Thanks,
Yunlong Song