Re: [PATCH 00/23] proc cleanup.

From: Eric W. Biederman
Date: Sat Feb 25 2006 - 10:19:33 EST

Andrew Morton <akpm@xxxxxxxx> writes:

> ebiederm@xxxxxxxxxxxx (Eric W. Biederman) wrote:
>>
>> When working on pid namespaces I keep tripping over /proc.
>> It's hard coded inode numbers and the amount of cruft
>> accumulated over the years makes it hard to deal with.
>>
>> So to put /proc out of my misery here is a series of patches that
>> removes the worst of the warts.
>
> An additional 2.7k of vmlinux. A shame.

Looks like that at least is compiler dependent, with gcc-3.3.5 I get:

text data bss dec hex filename
2601428 502342 226092 3329862 32cf46 ../linux-2.6-ns-mirror-build1/vmlinux
2602548 502494 226092 3331134 32d43e ../linux-2.6-ns-mirror-build2/vmlinux

So it looks like 1K of test and about 100 bytes of data.

Investigating this quickly. Because of the refactoring it
is hard to pin this down to any major culprit. But that is
also good news in that it doesn't look like an inline function
is responsible for this growth :)

It looks like the culprit for small amounts of growth is
the work to see if a task still exists, and other similar
checks that were needed but missing.

For the big chunks it looks like the work to populate the
dcache during readdir, which keeps the inode numbers in
sync and should help readdir+stat performance.

The other big culprit is proc_flush_task which is both
more comprehensive and simpler that proc_pid_flush+proc_pid_unhash=107+28.
But unfortunately that has made it a lot bigger.

So short of getting better dcache helpers for the case
where readdir populates the dcache it doesn't look the code
size will come down much.

The one practical thing that will help a little is that it
looks like with just a little more work we can replace
all of read_lock(&tasklist_lock) with rcu_read_lock().

add/remove: 33/23 grow/shrink: 28/16 up/down: 4968/-3619 (1349)
function old new delta
proc_flush_task - 605 +605
proc_check_dentry_visible - 325 +325
proc_fill_cache - 256 +256
proc_fd_instantiate - 243 +243
tref_get_by_task - 200 +200
first_tid - 179 +179
tgid_base_stuff 336 504 +168
tid_base_stuff 320 480 +160
first_tgid - 159 +159
proc_pident_instantiate - 158 +158
proc_task_instantiate - 128 +128
proc_pid_instantiate - 128 +128
attr_dir_stuff - 120 +120
proc_attr_dir_operations - 108 +108
tref_get_by_pid - 107 +107
proc_task_getattr - 105 +105
next_tid - 100 +100
next_tgid - 89 +89
tref_put - 87 +87
proc_attr_dir_inode_operations - 84 +84
do_maps_open - 80 +80
proc_fd_fill_cache - 63 +63
proc_task_fill_cache - 60 +60
proc_pid_fill_cache - 60 +60
__detach_pid 136 195 +59
proc_info_read 111 164 +53
oom_adjust_read 162 215 +53
proc_get_sb 26 78 +52
seccomp_write 168 218 +50
seccomp_read 164 214 +50
oom_adjust_write 164 214 +50
proc_pid_attr_read 124 172 +48
proc_base_stuff - 48 +48
proc_pid_attr_write 148 194 +46
proc_fd_link 122 168 +46
proc_exe_link 152 198 +46
mounts_open 157 200 +43
proc_root_link 99 141 +42
proc_cwd_link 99 141 +42
tid_fd_revalidate 207 247 +40
proc_pident_fill_cache - 40 +40
get_tref_task - 33 +33
dup_task_struct 137 170 +33
m_stop 59 88 +29
m_start 235 264 +29
tref_reset - 28 +28
proc_attr_dir_readdir - 28 +28
proc_pident_readdir 270 296 +26
proc_attr_dir_lookup - 22 +22
tref_set - 21 +21
tref_fini - 21 +21
tref_init - 18 +18
proc_pid_follow_link 98 116 +18
init_tref - 16 +16
init_task 1328 1344 +16
pid_revalidate 178 192 +14
attach_pid 149 162 +13
tref_get - 8 +8
mem_read 430 438 +8
proc_alloc_inode 98 102 +4
proc_task_readdir 320 323 +3
pid_delete_dentry 24 21 -3
m_next 70 61 -9
proc_readfd 327 307 -20
copy_process 3190 3170 -20
smaps_open 43 22 -21
maps_open 43 22 -21
proc_tid_attr_lookup 22 - -22
proc_tgid_attr_lookup 22 - -22
proc_delete_inode 129 105 -24
pid_base_dentry_operations 24 - -24
proc_tid_attr_readdir 28 - -28
proc_tgid_attr_readdir 28 - -28
proc_pid_flush 28 - -28
release_task 257 228 -29
proc_permission 38 - -38
proc_pid_make_inode 205 166 -39
unhash_process 73 33 -40
de_thread 1310 1266 -44
proc_check_root 55 - -55
proc_task_lookup 244 188 -56
pid_base_iput 62 - -62
proc_pid_readdir 303 229 -74
tid_attr_stuff 80 - -80
tgid_attr_stuff 80 - -80
proc_task_permission 82 - -82
proc_tid_attr_inode_operations 84 - -84
proc_tgid_attr_inode_operations 84 - -84
proc_mem_inode_operations 84 - -84
get_tid_list 97 - -97
proc_pid_unhash 107 - -107
proc_tid_attr_operations 108 - -108
proc_tgid_attr_operations 108 - -108
proc_lookupfd 240 99 -141
get_tgid_list 146 - -146
proc_task_root_link 218 - -218
proc_check_chroot 245 - -245
switch_exec_pids 290 - -290
proc_pid_lookup 503 145 -358
proc_pident_lookup 742 142 -600

Eric
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