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

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Date:   Tue, 8 Feb 2022 09:35:29 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] f2fs: avoid unneeded preflush during checkpoint()

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.

	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@...nel.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