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

[Chao Yu]

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@xxxxxxxxxx>
> > ---
> >   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