linux-kernel - [PATCH 4/4] f2fs: shrink size of struct seg

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Date:	Wed,  4 May 2016 23:19:48 +0800
From:	Chao Yu <chao@...nel.org>
To:	jaegeuk@...nel.org
Cc:	linux-f2fs-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: [PATCH 4/4] f2fs: shrink size of struct seg_entry

From: Chao Yu <yuchao0@...wei.com>

Restructure struct seg_entry to eliminate holes in it, after that,
in 32-bits machine, it reduces size from 32 bytes to 24 bytes; in
64-bits machine, it reduces size from 56 bytes to 40 bytes.

Signed-off-by: Chao Yu <yuchao0@...wei.com>
---
 fs/f2fs/segment.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
index 975c33d..7a756ff 100644
--- a/fs/f2fs/segment.h
+++ b/fs/f2fs/segment.h
@@ -158,16 +158,17 @@ struct victim_sel_policy {
 };
 
 struct seg_entry {
-	unsigned short valid_blocks;	/* # of valid blocks */
+	unsigned int type:6;		/* segment type like CURSEG_XXX_TYPE */
+	unsigned int valid_blocks:10;	/* # of valid blocks */
+	unsigned int ckpt_valid_blocks:10;	/* # of valid blocks last cp */
+	unsigned int padding:6;		/* padding */
 	unsigned char *cur_valid_map;	/* validity bitmap of blocks */
 	/*
 	 * # of valid blocks and the validity bitmap stored in the the last
 	 * checkpoint pack. This information is used by the SSR mode.
 	 */
-	unsigned short ckpt_valid_blocks;
-	unsigned char *ckpt_valid_map;
+	unsigned char *ckpt_valid_map;	/* validity bitmap of blocks last cp */
 	unsigned char *discard_map;
-	unsigned char type;		/* segment type like CURSEG_XXX_TYPE */
 	unsigned long long mtime;	/* modification time of the segment */
 };
 
-- 
2.7.2