From 12d40e43d251de4fa1f982567fc8b4ee5e858367 Mon Sep 17 00:00:00 2001 From: Arnaldo Carvalho de Melo Date: Wed, 6 Dec 2006 20:39:53 -0800 Subject: [PATCH] [PATCH] Save some bytes in struct inode [acme@newtoy net-2.6.20]$ pahole --cacheline 64 fs/inode.o inode /* /pub/scm/linux/kernel/git/acme/net-2.6.20/include/linux/dcache.h:86 */ struct inode { struct hlist_node i_hash; /* 0 8 */ struct list_head i_list; /* 8 8 */ struct list_head i_sb_list; /* 16 8 */ struct list_head i_dentry; /* 24 8 */ long unsigned int i_ino; /* 32 4 */ atomic_t i_count; /* 36 4 */ umode_t i_mode; /* 40 2 */ /* XXX 2 bytes hole, try to pack */ unsigned int i_nlink; /* 44 4 */ uid_t i_uid; /* 48 4 */ gid_t i_gid; /* 52 4 */ dev_t i_rdev; /* 56 4 */ loff_t i_size; /* 60 8 */ struct timespec i_atime; /* 68 8 */ struct timespec i_mtime; /* 76 8 */ struct timespec i_ctime; /* 84 8 */ unsigned int i_blkbits; /* 92 4 */ long unsigned int i_version; /* 96 4 */ blkcnt_t i_blocks; /* 100 4 */ short unsigned int i_bytes; /* 104 2 */ /* XXX 2 bytes hole, try to pack */ spinlock_t i_lock; /* 108 40 */ struct mutex i_mutex; /* 148 76 */ struct rw_semaphore i_alloc_sem; /* 224 64 */ struct inode_operations * i_op; /* 288 4 */ const struct file_operations * i_fop; /* 292 4 */ struct super_block * i_sb; /* 296 4 */ struct file_lock * i_flock; /* 300 4 */ struct address_space * i_mapping; /* 304 4 */ struct address_space i_data; /* 308 188 */ struct list_head i_devices; /* 496 8 */ union ; /* 504 4 */ int i_cindex; /* 508 4 */ __u32 i_generation; /* 512 4 */ /* ---------- cacheline 8 boundary ---------- */ long unsigned int i_dnotify_mask; /* 516 4 */ struct dnotify_struct * i_dnotify; /* 520 4 */ struct list_head inotify_watches; /* 524 8 */ struct mutex inotify_mutex; /* 532 76 */ long unsigned int i_state; /* 608 4 */ long unsigned int dirtied_when; /* 612 4 */ unsigned int i_flags; /* 616 4 */ atomic_t i_writecount; /* 620 4 */ void * i_security; /* 624 4 */ void * i_private; /* 628 4 */ }; /* size: 632, sum members: 628, holes: 2, sum holes: 4 */ [acme@newtoy net-2.6.20]$ So just moving i_mode to after i_bytes we save 4 bytes by nuking both holes: [acme@newtoy net-2.6.20]$ codiff -V /tmp/inode.o.before fs/inode.o /pub/scm/linux/kernel/git/acme/net-2.6.20/fs/inode.c: struct inode | -4 i_mode; from: umode_t /* 40(0) 2(0) */ to: umode_t /* 102(0) 2(0) */ 1 struct changed [acme@newtoy net-2.6.20]$ I've prunned all the other offset changes, only this one is of interest here. So now we have: [acme@newtoy net-2.6.20]$ pahole --cacheline 64 ../OUTPUT/qemu/net-2.6.20/fs/inode.o inode /* /pub/scm/linux/kernel/git/acme/net-2.6.20/include/linux/dcache.h:86 */ struct inode { struct hlist_node i_hash; /* 0 8 */ struct list_head i_list; /* 8 8 */ struct list_head i_sb_list; /* 16 8 */ struct list_head i_dentry; /* 24 8 */ long unsigned int i_ino; /* 32 4 */ atomic_t i_count; /* 36 4 */ unsigned int i_nlink; /* 40 4 */ uid_t i_uid; /* 44 4 */ gid_t i_gid; /* 48 4 */ dev_t i_rdev; /* 52 4 */ loff_t i_size; /* 56 8 */ /* ---------- cacheline 1 boundary ---------- */ struct timespec i_atime; /* 64 8 */ struct timespec i_mtime; /* 72 8 */ struct timespec i_ctime; /* 80 8 */ unsigned int i_blkbits; /* 88 4 */ long unsigned int i_version; /* 92 4 */ blkcnt_t i_blocks; /* 96 4 */ short unsigned int i_bytes; /* 100 2 */ umode_t i_mode; /* 102 2 */ spinlock_t i_lock; /* 104 40 */ struct mutex i_mutex; /* 144 76 */ struct rw_semaphore i_alloc_sem; /* 220 64 */ struct inode_operations * i_op; /* 284 4 */ const struct file_operations * i_fop; /* 288 4 */ struct super_block * i_sb; /* 292 4 */ struct file_lock * i_flock; /* 296 4 */ struct address_space * i_mapping; /* 300 4 */ struct address_space i_data; /* 304 188 */ struct list_head i_devices; /* 492 8 */ union ; /* 500 4 */ int i_cindex; /* 504 4 */ __u32 i_generation; /* 508 4 */ /* ---------- cacheline 8 boundary ---------- */ long unsigned int i_dnotify_mask; /* 512 4 */ struct dnotify_struct * i_dnotify; /* 516 4 */ struct list_head inotify_watches; /* 520 8 */ struct mutex inotify_mutex; /* 528 76 */ long unsigned int i_state; /* 604 4 */ long unsigned int dirtied_when; /* 608 4 */ unsigned int i_flags; /* 612 4 */ atomic_t i_writecount; /* 616 4 */ void * i_security; /* 620 4 */ void * i_private; /* 624 4 */ }; /* size: 628 */ [acme@newtoy net-2.6.20]$ Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/fs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 3a1927e516..70b99fbb56 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -543,7 +543,6 @@ struct inode { struct list_head i_dentry; unsigned long i_ino; atomic_t i_count; - umode_t i_mode; unsigned int i_nlink; uid_t i_uid; gid_t i_gid; @@ -559,6 +558,7 @@ struct inode { unsigned int i_blkbits; blkcnt_t i_blocks; unsigned short i_bytes; + umode_t i_mode; spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */ struct mutex i_mutex; struct rw_semaphore i_alloc_sem; -- 2.39.5