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.
>
> 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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