RE:(2) [PATCH] libf2fs: Fix calculation of usable segments for single zoned

[Yonggil Song]

> On 2024/10/7 13:21, Yonggil Song wrote:
> > There was a bug that did not subtract the super block area when calculating
> > the usable segments for a single zoned device with a conventional zone.
> > This bug resulted in incorrect the overprovision and reserved area.
> > 
> > 	<256MiB legacy block + zoned block w/ 32MiB zone size>
> > 	Info: Overprovision ratio = 3.570%
> > 	Info: Overprovision segments = 656 (GC reserved = 560)
> > 
> > 	<8 conventional zone + 1016 sequential zone w/ 32MiB zone size>
> > 	Info: Overprovision ratio = 3.700%
> > 	Info: Overprovision segments = 676 (GC reserved = 578)
> > 
> > This patch fixes the bug by subtracting the super block area when there is
> > only one zoned device.
> > 
> > Signed-off-by: Yonggil Song <yonggil.song@xxxxxxxxxxx>
> > ---
> >   lib/libf2fs_zoned.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/lib/libf2fs_zoned.c b/lib/libf2fs_zoned.c
> > index 89ba5ad73a76..cc5c064b7e3e 100644
> > --- a/lib/libf2fs_zoned.c
> > +++ b/lib/libf2fs_zoned.c
> > @@ -555,6 +555,11 @@ uint32_t f2fs_get_usable_segments(struct f2fs_super_block *sb)
> >   	}
> >   	usable_segs -= (get_sb(main_blkaddr) - get_sb(segment0_blkaddr)) >>
> >   						get_sb(log_blocks_per_seg);
> > +
> > +	/* single zoned device needs to remove a super block area */
> 
> If we don't format zoned device, it doesn't need to do this?
> 
> Thanks,
> 
Yes, single zoned block only needs this.

legacy block just return a segment_count_main.

thanks.
> > +	if (c.ndevs == 1)
>  > +		usable_segs -= (get_sb(segment0_blkaddr) >> get_sb(log_blocks_per_seg));> +
> >   	return usable_segs;
> >   #endif
> >   	return get_sb(segment_count_main);