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

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Message-ID: <20241007052122epcms2p8a7a733c92a8da751ac64af8a29de0303@epcms2p8>
Date: Mon, 07 Oct 2024 14:21:22 +0900
From: Yonggil Song <yonggil.song@...sung.com>
To: "jaegeuk@...nel.org" <jaegeuk@...nel.org>, "chao@...nel.org"
	<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>,
	Yonggil Song <yonggil.song@...sung.com>, Siwoo Jung <siu.jung@...sung.com>,
	Daejun Park <daejun7.park@...sung.com>
Subject: [PATCH] libf2fs: Fix calculation of usable segments for single
 zoned

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@...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..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 (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);
-- 
2.43.0