linux-kernel - Re: [PATCH v2] libf2fs: Fix calculation of usable segments for single

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Message-ID: <ZwlFkBAV2yxf1DBt@google.com>
Date: Fri, 11 Oct 2024 15:34:40 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Yonggil Song <yonggil.song@...sung.com>
Cc: Chao Yu <chao@...nel.org>,
	"linux-f2fs-devel@...ts.sourceforge.net" <linux-f2fs-devel@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dongjin Kim <dongjin_.kim@...sung.com>,
	Siwoo Jung <siu.jung@...sung.com>,
	Daejun Park <daejun7.park@...sung.com>
Subject: Re: [PATCH v2] libf2fs: Fix calculation of usable segments for single

On 10/10, Yonggil Song wrote:
> There was a problem that did not subtract the super block area when calculating
> the usable segments for a single zoned device with a conventional zone.
> This 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 addresses the problem by subtracting the super block area when
> there is only one zoned device.
> 
> Signed-off-by: Yonggil Song <yonggil.song@...sung.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..1a0985378789 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 (c.ndevs == 1 && c.devices[0].zoned_model == F2FS_ZONED_HM)

Does this work?

> +		usable_segs -= (get_sb(segment0_blkaddr) >> get_sb(log_blocks_per_seg));
> +
>  	return usable_segs;
>  #endif
>  	return get_sb(segment_count_main);
> -- 
> 2.43.0