On 2017/2/26 3:56, Jaegeuk Kim wrote:
> On 02/25, guoweichao wrote:
>> Hi Jaegeuk,
>>
>> I regard no enough free sections as a precondition when talking about
>> BG_GC -> FG_GC. I mean that for both case a) and b) I mentioned has no enough
>> free sections implicitly.
>>
>> On 2017/2/25 2:49, Jaegeuk Kim wrote:
>>> Hi Weichao,
>>>
>>> On 02/25, Weichao Guo wrote:
>>>> When turning to FG_GC from BG_GC, we need to write checkpoint in 2 cases:
>>>> * a) BG_GC have made some progress, e.g.: some prefree segments.
>>>> * b) There is no victim and no prefree segment.
>>>
>>> You missed
>>> * c) has_not_enough_free_secs() introduced by
>>> 6e17bfbc75a5cb ("f2fs: fix to overcome inline_data floods")
>> As we have enabled SSR for warm node(5b6c6be2d8 ("f2fs: use SSR for warm
>> node as well")),
>> I think inline data floods should not be a problem in most cases.
>>>
>>> And, Yunlong pointed that we can't find a case to avoid write_checkpoint()
>>> mostly due to c) condition.
>> As inline data floods is an extreme case, and there is little possibility
>> caused panic
>> for inline data floods now, there should be lots of chance to skip
>> checkpoint. I mean
>> that we can make some accurate inline data floods checking before writing
>> checkpoint.
>
> For now, the safest way is our first option. So, I decided to start with doing
> checkpoint due to previous inline_data flooding issue even though it's an
> extreme case under SSR.
>
> Anyway, I agree that we need to find a way to detect when to avoid checkpoint.
Hi all,
I proposed a approach before, can you please check that one?
https://www.mail-archive.com/linux-f2fs-devel@lists.sourceforge.net/msg03632.html
Thanks,
>
> Thanks,
>
>>>
>>> Thanks,
>>>
>>>>
>>>> For case a), previously, we also check if there is a dirty segment for
>>>> infering blocks moving in last BG_GC. But dirty segments do not always
>>>> indicate that, BG_GC may just start and do not move any blocks at all.
>>>> Futhermore, skipping checkpoint if there are some dirty segments but no
>>>> prefree segments is OK.
>>>
>>>
>>>>
>>>> Signed-off-by: Weichao Guo <guoweic...@huawei.com>
>>>> ---
>>>> fs/f2fs/gc.c | 7 ++++++-
>>>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>>> index 6c996e3..30d206a 100644
>>>> --- a/fs/f2fs/gc.c
>>>> +++ b/fs/f2fs/gc.c
>>>> @@ -958,7 +958,12 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync, bool
>>>> background)
>>>> * enough free sections, we should flush dent/node blocks and do
>>>> * garbage collections.
>>>> */
>>>> - ret = write_checkpoint(sbi, &cpc);
>>>> + if (prefree_segments(sbi))
>>>> + ret = write_checkpoint(sbi, &cpc);
>>>> + else if (!__get_victim(sbi, &segno, gc_type) {
>>>> + segno = NULL_SEGNO;
>>>> + ret = write_checkpoint(sbi, &cpc);
>>>> + }
>>>> if (ret)
>>>> goto stop;
>>>> } else if (gc_type == BG_GC && !background) {
>>>> --
>>>> 2.10.1
>>>
>>> .
>>>
>>
>> Thanks,
>> Weichao
>
> .
>
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