On Wed, Dec 20, 2017 at 03:10:48PM -0800, Randy Dunlap wrote: > On 12/20/2017 01:59 PM, Alexey Dobriyan wrote: > > struct proc_dir_entry became bit messy over years: > > > > * move 16-bit ->mode_t before namelen to get rid of padding > > * make ->in_use first field: it seems to be most used resulting in > > smaller code on x86_64 (defconfig): > > > > add/remove: 0/0 grow/shrink: 7/13 up/down: 24/-67 (-43) > > Function old new delta > > proc_readdir_de 451 455 +4 > > proc_get_inode 282 286 +4 > > pde_put 65 69 +4 > > remove_proc_subtree 294 297 +3 > > remove_proc_entry 297 300 +3 > > proc_register 295 298 +3 > > proc_notify_change 94 97 +3 > > unuse_pde 27 26 -1 > > proc_reg_write 89 85 -4 > > proc_reg_unlocked_ioctl 85 81 -4 > > proc_reg_read 89 85 -4 > > proc_reg_llseek 87 83 -4 > > proc_reg_get_unmapped_area 123 119 -4 > > proc_entry_rundown 139 135 -4 > > proc_reg_poll 91 85 -6 > > proc_reg_mmap 79 73 -6 > > proc_get_link 55 49 -6 > > proc_reg_release 108 101 -7 > > proc_reg_open 298 291 -7 > > close_pdeo 228 218 -10 > > > > * move writeable fields together to a first cacheline (on x86_64), > > those include > > * ->in_use: reference count, taken every open/read/write/close etc > > * ->count: reference count, taken at readdir on every entry > > * ->pde_openers: tracks (nearly) every open, dirtied > > * ->pde_unload_lock: spinlock protecting ->pde_openers > > * ->proc_iops, ->proc_fops, ->data: writeonce fields, > > used right together with previous group. > > > > * other rarely written fields go into 1st/2nd and 2nd/3rd cacheline on > > 32-bit and 64-bit respectively. > > > > Additionally on 32-bit, ->subdir, ->subdir_node, ->namelen, ->name > > go fully into 2nd cacheline, separated from writeable fields. > > They are all used during lookup. > > Does > > } __randomize_layout; > pay attention to any of that?
No. You can randomize inside cachelines but it will look rather ugly. __randomize_layout rearranges everything.
