Messages in this thread | | | Subject | Re: [f2fs-dev] [PATCH 3/3] f2fs: skip migration only when BG_GC is called | From | Chao Yu <> | Date | Tue, 25 Feb 2020 10:24:17 +0800 |
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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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