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

[Chao Yu]

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@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
>
>
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