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SubjectRe: [f2fs-dev] [PATCH 3/3] f2fs: skip migration only when BG_GC is called
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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.

Thanks,

>
>>
>> Thanks,
>>
>>> goto skip;
>>> if (!PageUptodate(sum_page) || unlikely(f2fs_cp_error(sbi)))
>>>
> .
>

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