memcg was reported years ago to have significant overhead when unused. It has improved but it's still the case that users that have no knowledge of memcg pay a performance penalty. This patch adds a Kconfig that controls whether memcg is enabled by default and a kernel parameter cgroup_enable= to enable it if desired. Anyone using oldconfig will get the historical behaviour. It is not an option for most distributions to simply disable MEMCG as there are users that require it but they should also be knowledgable enough to use cgroup_enable=. This was evaluated using aim9, a page fault microbenchmark and ebizzy but I'll focus on the page fault microbenchmark. It can be reproduced using pft from mmtests (https://github.com/gormanm/mmtests). Edit configs/config-global-dhp__pagealloc-performance and update MMTESTS to only contain pft. This is the relevant part of the profile summary /usr/src/linux-4.0-vanilla/mm/memcontrol.c 6.6441 395842 mem_cgroup_try_charge 2.950% 175781 __mem_cgroup_count_vm_event 1.431% 85239 mem_cgroup_page_lruvec 0.456% 27156 mem_cgroup_commit_charge 0.392% 23342 uncharge_list 0.323% 19256 mem_cgroup_update_lru_size 0.278% 16538 memcg_check_events 0.216% 12858 mem_cgroup_charge_statistics.isra.22 0.188% 11172 try_charge 0.150% 8928 commit_charge 0.141% 8388 get_mem_cgroup_from_mm 0.121% 7184 It's showing 6.64% overhead in memcontrol.c when no memcgs are in use. Applying the patch and disabling memcg reduces this to 0.48% /usr/src/linux-4.0-nomemcg-v1r1/mm/memcontrol.c 0.4834 27511 mem_cgroup_page_lruvec 0.161% 9172 mem_cgroup_update_lru_size 0.154% 8794 mem_cgroup_try_charge 0.126% 7194 mem_cgroup_commit_charge 0.041% 2351 Note that it's not very visible from headline performance figures pft faults 4.0.0 4.0.0 vanilla nomemcg-v1 Hmean faults/cpu-1 1443258.1051 ( 0.00%) 1530574.6033 ( 6.05%) Hmean faults/cpu-3 1340385.9270 ( 0.00%) 1375156.5834 ( 2.59%) Hmean faults/cpu-5 875599.0222 ( 0.00%) 876217.9211 ( 0.07%) Hmean faults/cpu-7 601146.6726 ( 0.00%) 599068.4360 ( -0.35%) Hmean faults/cpu-8 510728.2754 ( 0.00%) 509887.9960 ( -0.16%) Hmean faults/sec-1 1432084.7845 ( 0.00%) 1518566.3541 ( 6.04%) Hmean faults/sec-3 3943818.1437 ( 0.00%) 4036918.0217 ( 2.36%) Hmean faults/sec-5 3877573.5867 ( 0.00%) 3922745.9207 ( 1.16%) Hmean faults/sec-7 3991832.0418 ( 0.00%) 3990670.8481 ( -0.03%) Hmean faults/sec-8 3987189.8167 ( 0.00%) 3978842.8107 ( -0.21%) Low thread counts get a boost but it's within noise as memcg overhead does not dominate. It's not obvious at all at higher thread counts as other factors cause more problems. The overall breakdown of CPU usage looks like 4.0.0 4.0.0 vanilla nomemcg-v1 User 41.45 41.11 System 410.19 404.76 Elapsed 130.33 126.30 Despite the relative unimportance, there is at least some justification for disabling memcg by default. Signed-off-by: Mel Gorman <mgorman@xxxxxxx> --- Documentation/kernel-parameters.txt | 4 ++++ init/Kconfig | 15 +++++++++++++++ kernel/cgroup.c | 20 ++++++++++++++++---- mm/memcontrol.c | 3 +++ 4 files changed, 38 insertions(+), 4 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index bfcb1a62a7b4..4f264f906816 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -591,6 +591,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. cut the overhead, others just disable the usage. So only cgroup_disable=memory is actually worthy} + cgroup_enable= [KNL] Enable a particular controller + Similar to cgroup_disable except that it enables + controllers that are disabled by default. + checkreqprot [SELINUX] Set initial checkreqprot flag value. Format: { "0" | "1" } See security/selinux/Kconfig help text. diff --git a/init/Kconfig b/init/Kconfig index f5dbc6d4261b..819b6cc05cba 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -990,6 +990,21 @@ config MEMCG Provides a memory resource controller that manages both anonymous memory and page cache. (See Documentation/cgroups/memory.txt) +config MEMCG_DEFAULT_ENABLED + bool "Automatically enable memory resource controller" + default y + depends on MEMCG + help + The memory controller has some overhead even if idle as resource + usage must be tracked in case a group is created and a process + migrated. As users may not be aware of this and the cgroup_disable= + option, this config option controls whether it is enabled by + default. It is assumed that someone that requires the controller + can find the cgroup_enable= switch. + + Say N if unsure. This is default Y to preserve oldconfig and + historical behaviour. + config MEMCG_SWAP bool "Memory Resource Controller Swap Extension" depends on MEMCG && SWAP diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 29a7b2cc593e..0e79db55bf1a 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -5370,7 +5370,7 @@ out_free: kfree(pathbuf); } -static int __init cgroup_disable(char *str) +static int __init __cgroup_set_state(char *str, bool disabled) { struct cgroup_subsys *ss; char *token; @@ -5382,16 +5382,28 @@ static int __init cgroup_disable(char *str) for_each_subsys(ss, i) { if (!strcmp(token, ss->name)) { - ss->disabled = 1; - printk(KERN_INFO "Disabling %s control group" - " subsystem\n", ss->name); + ss->disabled = disabled; + printk(KERN_INFO "Setting %s control group" + " subsystem %s\n", ss->name, + disabled ? "disabled" : "enabled"); break; } } } return 1; } + +static int __init cgroup_disable(char *str) +{ + return __cgroup_set_state(str, true); +} + +static int __init cgroup_enable(char *str) +{ + return __cgroup_set_state(str, false); +} __setup("cgroup_disable=", cgroup_disable); +__setup("cgroup_enable=", cgroup_enable); static int __init cgroup_set_legacy_files_on_dfl(char *str) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index b34ef4a32a3b..ce171ba16949 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5391,6 +5391,9 @@ struct cgroup_subsys memory_cgrp_subsys = { .dfl_cftypes = memory_files, .legacy_cftypes = mem_cgroup_legacy_files, .early_init = 0, +#ifndef CONFIG_MEMCG_DEFAULT_ENABLED + .disabled = 1, +#endif }; /** -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>