Re: [f2fs-dev] [PATCH] f2fs: avoid unneeded preflush during checkpoint()

[Chao Yu <chao@kernel.org>]

On 2022/2/8 9:35, Chao Yu wrote:
> On 2022/2/8 3:14, Jaegeuk Kim wrote:
>> On 02/07, Chao Yu wrote:
>>> During checkpoint, we have committed preflush command via f2fs_flush_device_cache()
>>
>>   787 int f2fs_flush_device_cache(struct f2fs_sb_info *sbi)
>>   788 {
>>   789         int ret = 0, i;
>>   790
>>   791         if (!f2fs_is_multi_device(sbi))
>>   792                 return 0;
>>
>> Seems a wrong assumption.
> 
> Oh, I missed that f2fs_flush_device_cache was introduced to flush devices except
> first device when multi-device feature is on.
> 
>      for (i = 1; i < sbi->s_ndevs; i++) {
>          int count = DEFAULT_RETRY_IO_COUNT;
> 
> So, this patch seems wrong...
> 
> Instead, below case looks wrong since it needs to trigger flush during checkpoint()
> no matter nobarrier is on or off.

Wrong comments, let's ignore this patch, sorry.

Thanks,

> 
>      if (test_opt(sbi, NOBARRIER))
>          return 0;
> 
> Thanks,
> 
>>
>>> to persist all metadata pages except last #2 CP pack page, so we don't need to
>>> commit another preflush command in commit_checkpoint(), remove it to avoid unneeded
>>> write cache overhead.
>>>
>>> Signed-off-by: Chao Yu <chao@kernel.org>
>>> ---
>>>   fs/f2fs/data.c | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 8c417864c66a..15ac18bbbc8e 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -598,7 +598,7 @@ static void __f2fs_submit_merged_write(struct f2fs_sb_info *sbi,
>>>           io->fio.op = REQ_OP_WRITE;
>>>           io->fio.op_flags = REQ_META | REQ_PRIO | REQ_SYNC;
>>>           if (!test_opt(sbi, NOBARRIER))
>>> -            io->fio.op_flags |= REQ_PREFLUSH | REQ_FUA;
>>> +            io->fio.op_flags |= REQ_FUA;
>>>       }
>>>       __submit_merged_bio(io);
>>>       up_write(&io->io_rwsem);
>>> -- 
>>> 2.32.0
> 
> 
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