Re: [PATCH] libf2fs: Fix calculation of usable segments for single zoned

[Chao Yu <chao@kernel.org>]

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@samsung.com>
> ---
>   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,

> +	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);