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 <jaeg...@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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