)]}' { "commit": "36de6437866bbb1d37e2312ff4f95ee4ed6d2b61", "tree": "5e77ff1af2ccaaeaba09d9aa0d9f10732207e865", "parents": [ "33f2ef89f8e181486b63fdbdc97c6afa6ca9f34b" ], "author": { "name": "Arnaldo Carvalho de Melo", "email": "acme@mandriva.com", "time": "Wed Dec 06 20:33:42 2006 -0800" }, "committer": { "name": "Linus Torvalds", "email": "torvalds@woody.osdl.org", "time": "Thu Dec 07 08:39:25 2006 -0800" }, "message": "[PATCH] Save some bytes in struct mm_struct\n\nBefore:\n[acme@newtoy net-2.6.20]$ pahole --cacheline 32 kernel/sched.o mm_struct\n\n/* include2/asm/processor.h:542 */\nstruct mm_struct {\n struct vm_area_struct * mmap; /* 0 4 */\n struct rb_root mm_rb; /* 4 4 */\n struct vm_area_struct * mmap_cache; /* 8 4 */\n long unsigned int (*get_unmapped_area)(); /* 12 4 */\n void (*unmap_area)(); /* 16 4 */\n long unsigned int mmap_base; /* 20 4 */\n long unsigned int task_size; /* 24 4 */\n long unsigned int cached_hole_size; /* 28 4 */\n /* ---------- cacheline 1 boundary ---------- */\n long unsigned int free_area_cache; /* 32 4 */\n pgd_t * pgd; /* 36 4 */\n atomic_t mm_users; /* 40 4 */\n atomic_t mm_count; /* 44 4 */\n int map_count; /* 48 4 */\n struct rw_semaphore mmap_sem; /* 52 64 */\n spinlock_t page_table_lock; /* 116 40 */\n struct list_head mmlist; /* 156 8 */\n mm_counter_t _file_rss; /* 164 4 */\n mm_counter_t _anon_rss; /* 168 4 */\n long unsigned int hiwater_rss; /* 172 4 */\n long unsigned int hiwater_vm; /* 176 4 */\n long unsigned int total_vm; /* 180 4 */\n long unsigned int locked_vm; /* 184 4 */\n long unsigned int shared_vm; /* 188 4 */\n /* ---------- cacheline 6 boundary ---------- */\n long unsigned int exec_vm; /* 192 4 */\n long unsigned int stack_vm; /* 196 4 */\n long unsigned int reserved_vm; /* 200 4 */\n long unsigned int def_flags; /* 204 4 */\n long unsigned int nr_ptes; /* 208 4 */\n long unsigned int start_code; /* 212 4 */\n long unsigned int end_code; /* 216 4 */\n long unsigned int start_data; /* 220 4 */\n /* ---------- cacheline 7 boundary ---------- */\n long unsigned int end_data; /* 224 4 */\n long unsigned int start_brk; /* 228 4 */\n long unsigned int brk; /* 232 4 */\n long unsigned int start_stack; /* 236 4 */\n long unsigned int arg_start; /* 240 4 */\n long unsigned int arg_end; /* 244 4 */\n long unsigned int env_start; /* 248 4 */\n long unsigned int env_end; /* 252 4 */\n /* ---------- cacheline 8 boundary ---------- */\n long unsigned int saved_auxv[44]; /* 256 176 */\n unsigned int dumpable:2; /* 432 4 */\n cpumask_t cpu_vm_mask; /* 436 4 */\n mm_context_t context; /* 440 68 */\n long unsigned int swap_token_time; /* 508 4 */\n /* ---------- cacheline 16 boundary ---------- */\n char recent_pagein; /* 512 1 */\n\n /* XXX 3 bytes hole, try to pack */\n\n int core_waiters; /* 516 4 */\n struct completion * core_startup_done; /* 520 4 */\n struct completion core_done; /* 524 52 */\n rwlock_t ioctx_list_lock; /* 576 36 */\n struct kioctx * ioctx_list; /* 612 4 */\n}; /* size: 616, sum members: 613, holes: 1, sum holes: 3, cachelines: 20,\n last cacheline: 8 bytes */\n\nAfter:\n\n[acme@newtoy net-2.6.20]$ pahole --cacheline 32 kernel/sched.o mm_struct\n/* include2/asm/processor.h:542 */\nstruct mm_struct {\n struct vm_area_struct * mmap; /* 0 4 */\n struct rb_root mm_rb; /* 4 4 */\n struct vm_area_struct * mmap_cache; /* 8 4 */\n long unsigned int (*get_unmapped_area)(); /* 12 4 */\n void (*unmap_area)(); /* 16 4 */\n long unsigned int mmap_base; /* 20 4 */\n long unsigned int task_size; /* 24 4 */\n long unsigned int cached_hole_size; /* 28 4 */\n /* ---------- cacheline 1 boundary ---------- */\n long unsigned int free_area_cache; /* 32 4 */\n pgd_t * pgd; /* 36 4 */\n atomic_t mm_users; /* 40 4 */\n atomic_t mm_count; /* 44 4 */\n int map_count; /* 48 4 */\n struct rw_semaphore mmap_sem; /* 52 64 */\n spinlock_t page_table_lock; /* 116 40 */\n struct list_head mmlist; /* 156 8 */\n mm_counter_t _file_rss; /* 164 4 */\n mm_counter_t _anon_rss; /* 168 4 */\n long unsigned int hiwater_rss; /* 172 4 */\n long unsigned int hiwater_vm; /* 176 4 */\n long unsigned int total_vm; /* 180 4 */\n long unsigned int locked_vm; /* 184 4 */\n long unsigned int shared_vm; /* 188 4 */\n /* ---------- cacheline 6 boundary ---------- */\n long unsigned int exec_vm; /* 192 4 */\n long unsigned int stack_vm; /* 196 4 */\n long unsigned int reserved_vm; /* 200 4 */\n long unsigned int def_flags; /* 204 4 */\n long unsigned int nr_ptes; /* 208 4 */\n long unsigned int start_code; /* 212 4 */\n long unsigned int end_code; /* 216 4 */\n long unsigned int start_data; /* 220 4 */\n /* ---------- cacheline 7 boundary ---------- */\n long unsigned int end_data; /* 224 4 */\n long unsigned int start_brk; /* 228 4 */\n long unsigned int brk; /* 232 4 */\n long unsigned int start_stack; /* 236 4 */\n long unsigned int arg_start; /* 240 4 */\n long unsigned int arg_end; /* 244 4 */\n long unsigned int env_start; /* 248 4 */\n long unsigned int env_end; /* 252 4 */\n /* ---------- cacheline 8 boundary ---------- */\n long unsigned int saved_auxv[44]; /* 256 176 */\n cpumask_t cpu_vm_mask; /* 432 4 */\n mm_context_t context; /* 436 68 */\n long unsigned int swap_token_time; /* 504 4 */\n char recent_pagein; /* 508 1 */\n unsigned char dumpable:2; /* 509 1 */\n\n /* XXX 2 bytes hole, try to pack */\n\n int core_waiters; /* 512 4 */\n struct completion * core_startup_done; /* 516 4 */\n struct completion core_done; /* 520 52 */\n rwlock_t ioctx_list_lock; /* 572 36 */\n struct kioctx * ioctx_list; /* 608 4 */\n}; /* size: 612, sum members: 610, holes: 1, sum holes: 2, cachelines: 20,\n last cacheline: 4 bytes */\n\n[acme@newtoy net-2.6.20]$ codiff -V /tmp/sched.o.before kernel/sched.o\n/pub/scm/linux/kernel/git/acme/net-2.6.20/kernel/sched.c:\n struct mm_struct | -4\n dumpable:2;\n from: unsigned int /* 432(30) 4(2) */\n to: unsigned char /* 509(6) 1(2) */\n\u003c SNIP other offset changes \u003e\n 1 struct changed\n[acme@newtoy net-2.6.20]$\n\nI\u0027m not aware of any problem about using 2 byte wide bitfields where\npreviously a 4 byte wide one was, holler if there is any, I wouldn\u0027t be\nsurprised, bitfields are things from hell.\n\nFor the curious, 432(30) means: at offset 432 from the struct start, at\noffset 30 in the bitfield (yeah, it comes backwards, hellish, huh?) ditto\nfor 509(6), while 4(2) and 1(2) means \"struct field size(bitfield size)\".\n\nNow we have a 2 bytes hole and are using only 4 bytes of the last 32\nbytes cacheline, any takers? :-)\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": "cad6a16260f76f9115a3e893a804d0b3eb711c10", "old_mode": 33188, "old_path": "include/linux/sched.h", "new_id": "acfd2e15c5f27be9215dd5202a0cb93bc153d8d4", "new_mode": 33188, "new_path": "include/linux/sched.h" } ] }