)]}' { "commit": "12d40e43d251de4fa1f982567fc8b4ee5e858367", "tree": "91a562fc73af84efe6e8a388ccd2f907c04fa674", "parents": [ "652d3a3ed7610bb09530127ca297b538fe7d245a" ], "author": { "name": "Arnaldo Carvalho de Melo", "email": "acme@mandriva.com", "time": "Wed Dec 06 20:39:53 2006 -0800" }, "committer": { "name": "Linus Torvalds", "email": "torvalds@woody.osdl.org", "time": "Thu Dec 07 08:39:43 2006 -0800" }, "message": "[PATCH] Save some bytes in struct inode\n\n[acme@newtoy net-2.6.20]$ pahole --cacheline 64 fs/inode.o inode\n/* /pub/scm/linux/kernel/git/acme/net-2.6.20/include/linux/dcache.h:86 */\nstruct inode {\n struct hlist_node i_hash; /* 0 8 */\n struct list_head i_list; /* 8 8 */\n struct list_head i_sb_list; /* 16 8 */\n struct list_head i_dentry; /* 24 8 */\n long unsigned int i_ino; /* 32 4 */\n atomic_t i_count; /* 36 4 */\n umode_t i_mode; /* 40 2 */\n\n /* XXX 2 bytes hole, try to pack */\n\n unsigned int i_nlink; /* 44 4 */\n uid_t i_uid; /* 48 4 */\n gid_t i_gid; /* 52 4 */\n dev_t i_rdev; /* 56 4 */\n loff_t i_size; /* 60 8 */\n struct timespec i_atime; /* 68 8 */\n struct timespec i_mtime; /* 76 8 */\n struct timespec i_ctime; /* 84 8 */\n unsigned int i_blkbits; /* 92 4 */\n long unsigned int i_version; /* 96 4 */\n blkcnt_t i_blocks; /* 100 4 */\n short unsigned int i_bytes; /* 104 2 */\n\n /* XXX 2 bytes hole, try to pack */\n\n spinlock_t i_lock; /* 108 40 */\n struct mutex i_mutex; /* 148 76 */\n struct rw_semaphore i_alloc_sem; /* 224 64 */\n struct inode_operations * i_op; /* 288 4 */\n const struct file_operations * i_fop; /* 292 4 */\n struct super_block * i_sb; /* 296 4 */\n struct file_lock * i_flock; /* 300 4 */\n struct address_space * i_mapping; /* 304 4 */\n struct address_space i_data; /* 308 188 */\n struct list_head i_devices; /* 496 8 */\n union ; /* 504 4 */\n int i_cindex; /* 508 4 */\n __u32 i_generation; /* 512 4 */\n /* ---------- cacheline 8 boundary ---------- */\n long unsigned int i_dnotify_mask; /* 516 4 */\n struct dnotify_struct * i_dnotify; /* 520 4 */\n struct list_head inotify_watches; /* 524 8 */\n struct mutex inotify_mutex; /* 532 76 */\n long unsigned int i_state; /* 608 4 */\n long unsigned int dirtied_when; /* 612 4 */\n unsigned int i_flags; /* 616 4 */\n atomic_t i_writecount; /* 620 4 */\n void * i_security; /* 624 4 */\n void * i_private; /* 628 4 */\n}; /* size: 632, sum members: 628, holes: 2, sum holes: 4 */\n\n[acme@newtoy net-2.6.20]$\n\nSo just moving i_mode to after i_bytes we save 4 bytes by nuking both holes:\n\n[acme@newtoy net-2.6.20]$ codiff -V /tmp/inode.o.before fs/inode.o\n/pub/scm/linux/kernel/git/acme/net-2.6.20/fs/inode.c:\n struct inode | -4\n i_mode;\n from: umode_t /* 40(0) 2(0) */\n to: umode_t /* 102(0) 2(0) */\n 1 struct changed\n[acme@newtoy net-2.6.20]$\n\nI\u0027ve prunned all the other offset changes, only this one is of interest here.\n\nSo now we have:\n\n[acme@newtoy net-2.6.20]$ pahole --cacheline 64 ../OUTPUT/qemu/net-2.6.20/fs/inode.o inode\n/* /pub/scm/linux/kernel/git/acme/net-2.6.20/include/linux/dcache.h:86 */\nstruct inode {\n struct hlist_node i_hash; /* 0 8 */\n struct list_head i_list; /* 8 8 */\n struct list_head i_sb_list; /* 16 8 */\n struct list_head i_dentry; /* 24 8 */\n long unsigned int i_ino; /* 32 4 */\n atomic_t i_count; /* 36 4 */\n unsigned int i_nlink; /* 40 4 */\n uid_t i_uid; /* 44 4 */\n gid_t i_gid; /* 48 4 */\n dev_t i_rdev; /* 52 4 */\n loff_t i_size; /* 56 8 */\n /* ---------- cacheline 1 boundary ---------- */\n struct timespec i_atime; /* 64 8 */\n struct timespec i_mtime; /* 72 8 */\n struct timespec i_ctime; /* 80 8 */\n unsigned int i_blkbits; /* 88 4 */\n long unsigned int i_version; /* 92 4 */\n blkcnt_t i_blocks; /* 96 4 */\n short unsigned int i_bytes; /* 100 2 */\n umode_t i_mode; /* 102 2 */\n spinlock_t i_lock; /* 104 40 */\n struct mutex i_mutex; /* 144 76 */\n struct rw_semaphore i_alloc_sem; /* 220 64 */\n struct inode_operations * i_op; /* 284 4 */\n const struct file_operations * i_fop; /* 288 4 */\n struct super_block * i_sb; /* 292 4 */\n struct file_lock * i_flock; /* 296 4 */\n struct address_space * i_mapping; /* 300 4 */\n struct address_space i_data; /* 304 188 */\n struct list_head i_devices; /* 492 8 */\n union ; /* 500 4 */\n int i_cindex; /* 504 4 */\n __u32 i_generation; /* 508 4 */\n /* ---------- cacheline 8 boundary ---------- */\n long unsigned int i_dnotify_mask; /* 512 4 */\n struct dnotify_struct * i_dnotify; /* 516 4 */\n struct list_head inotify_watches; /* 520 8 */\n struct mutex inotify_mutex; /* 528 76 */\n long unsigned int i_state; /* 604 4 */\n long unsigned int dirtied_when; /* 608 4 */\n unsigned int i_flags; /* 612 4 */\n atomic_t i_writecount; /* 616 4 */\n void * i_security; /* 620 4 */\n void * i_private; /* 624 4 */\n}; /* size: 628 */\n\n[acme@newtoy net-2.6.20]$\n\nSigned-off-by: Arnaldo Carvalho de Melo \u003cacme@mandriva.com\u003e\nSigned-off-by: Andrew Morton \u003cakpm@osdl.org\u003e\nSigned-off-by: Linus Torvalds \u003ctorvalds@osdl.org\u003e\n", "tree_diff": [ { "type": "modify", "old_id": "3a1927e516d041ad4b7e0197f729cd81b2043acd", "old_mode": 33188, "old_path": "include/linux/fs.h", "new_id": "70b99fbb560bc4aba52e0013900d5534b77a6038", "new_mode": 33188, "new_path": "include/linux/fs.h" } ] }