From: Chao Yu <yuchao0@huawei.com>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 3/3] f2fs: skip migration only when BG_GC is called
Date: Tue, 25 Feb 2020 10:24:17 +0800 [thread overview]
Message-ID: <141fb1b0-b527-1ef8-0fce-dcdf0170a987@huawei.com> (raw)
In-Reply-To: <20200224215341.GB77839@google.com>
On 2020/2/25 5:53, Jaegeuk Kim wrote:
> On 02/19, Chao Yu wrote:
>> On 2020/2/19 11:04, Jaegeuk Kim wrote:
>>> On 02/19, Chao Yu wrote:
>>>> On 2020/2/19 7:27, Jaegeuk Kim wrote:
>>>>> On 02/17, Chao Yu wrote:
>>>>>> On 2020/2/15 2:58, Jaegeuk Kim wrote:
>>>>>>> FG_GC needs to move entire section more quickly.
>>>>>>>
>>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>>>>>> ---
>>>>>>> fs/f2fs/gc.c | 2 +-
>>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>>>>> index bbf4db3f6bb4..1676eebc8c8b 100644
>>>>>>> --- a/fs/f2fs/gc.c
>>>>>>> +++ b/fs/f2fs/gc.c
>>>>>>> @@ -1203,7 +1203,7 @@ static int do_garbage_collect(struct f2fs_sb_info *sbi,
>>>>>>>
>>>>>>> if (get_valid_blocks(sbi, segno, false) == 0)
>>>>>>> goto freed;
>>>>>>> - if (__is_large_section(sbi) &&
>>>>>>> + if (gc_type == BG_GC && __is_large_section(sbi) &&
>>>>>>> migrated >= sbi->migration_granularity)
>>>>>>
>>>>>> I knew migrating one large section is a more efficient way, but this can
>>>>>> increase long-tail latency of f2fs_balance_fs() occasionally, especially in
>>>>>> extreme fragmented space.
>>>>>
>>>>> FG_GC requires to wait for whole section migration which shows the entire
>>>>> latency.
>>>>
>>>> That will cause long-tail latency for single f2fs_balance_fs() procedure,
>>>> which it looks a very long hang when userspace call f2fs syscall, so why
>>>> not splitting total elapsed time into several f2fs_balance_fs() to avoid that.
>>>
>>> Then, other ops can easily make more dirty segments. The intention of FG_GC is
>>
>> Yup, that's a problem, if there are more dirty datas being made, reserved segments
>> may be ran out during FG_GC.
>>
>>> to block everything and make min. free segments as a best shot.
>>
>> I just try to simulate write GC's logic in FTL to mitigate single op's max latency,
>> otherwise benchmark looks hang during FG_GC (in a 500mb+ section).
Oh, if we want to FG_GC only migrate on segment on time, it needs to change
has_not_enough_free_secs() condition as well, so previous logic is broken.
Nvm, please add:
Reviewed-by: Chao Yu <yuchao0@huawei.com>
>
> Hmm, I think we may need to think another way like doing BG_GC more aggressively.
Agreed, I guess SMR scenario may need such policy: higher trigger frequency on bggc
when free space decreases, but less block migration for each bggc cycle.
Thanks,
>
>>
>> Thanks,
>>
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>>> goto skip;
>>>>>>> if (!PageUptodate(sum_page) || unlikely(f2fs_cp_error(sbi)))
>>>>>>>
>>>>> .
>>>>>
>>> .
>>>
> .
>
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next prev parent reply other threads:[~2020-02-25 2:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-14 18:58 [f2fs-dev] [PATCH 1/3] f2fs: skip GC when section is full Jaegeuk Kim
2020-02-14 18:58 ` [f2fs-dev] [PATCH 2/3] f2fs: add migration count iff migration happens Jaegeuk Kim
2020-02-17 1:41 ` Chao Yu
2020-02-17 1:43 ` Chao Yu
2020-02-14 18:58 ` [f2fs-dev] [PATCH 3/3] f2fs: skip migration only when BG_GC is called Jaegeuk Kim
2020-02-17 2:22 ` Chao Yu
2020-02-18 23:27 ` Jaegeuk Kim
2020-02-19 3:01 ` Chao Yu
2020-02-19 3:04 ` Jaegeuk Kim
2020-02-19 3:54 ` Chao Yu
2020-02-24 21:53 ` Jaegeuk Kim
2020-02-25 2:24 ` Chao Yu [this message]
2020-02-17 1:40 ` [f2fs-dev] [PATCH 1/3] f2fs: skip GC when section is full Chao Yu
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