Re: [PATCH] Add cgroup support for enabling controllers at boot time

[Li Zefan <lizf@cn.fujitsu.com>]

Balbir Singh wrote:
> Li Zefan wrote:
>> Balbir Singh wrote:
>>> From: Paul Menage <menage@google.com>
>>>
>>> The effects of cgroup_disable=foo are:
>>>
>>> - foo doesn't show up in /proc/cgroups
>>> - foo isn't auto-mounted if you mount all cgroups in a single hierarchy
>>> - foo isn't visible as an individually mountable subsystem
>>>
>>> As a result there will only ever be one call to foo->create(), at init
>>> time; all processes will stay in this group, and the group will never
>>> be mounted on a visible hierarchy. Any additional effects (e.g. not
>>> allocating metadata) are up to the foo subsystem.
>>>
>>> This doesn't handle early_init subsystems (their "disabled" bit isn't
>>> set be, but it could easily be extended to do so if any of the early_init
>>> systems wanted it - I think it would just involve some nastier parameter
>>> processing since it would occur before the command-line argument parser
>>> had been run.
>>>
>>> [Balbir added Documentation/kernel-parameters updates]
>>>
>>> Signed-off-by: Paul Menage <menage@google.com>
>>> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
>>> ---
>>>
>>>  Documentation/kernel-parameters.txt |    4 ++++
>>>  include/linux/cgroup.h              |    1 +
>>>  kernel/cgroup.c                     |   27 +++++++++++++++++++++++++--
>>>  3 files changed, 30 insertions(+), 2 deletions(-)
>>>
>>> diff -puN include/linux/cgroup.h~cgroup_disable include/linux/cgroup.h
>>> --- linux-2.6.25-rc4/include/linux/cgroup.h~cgroup_disable   
>>> 2008-03-06 12:19:38.000000000 +0530
>>> +++ linux-2.6.25-rc4-balbir/include/linux/cgroup.h    2008-03-06
>>> 12:19:38.000000000 +0530
>>> @@ -256,6 +256,7 @@ struct cgroup_subsys {
>>>      void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
>>>      int subsys_id;
>>>      int active;
>>> +    int disabled;
>>>      int early_init;
>>>  #define MAX_CGROUP_TYPE_NAMELEN 32
>>>      const char *name;
>>> diff -puN kernel/cgroup.c~cgroup_disable kernel/cgroup.c
>>> --- linux-2.6.25-rc4/kernel/cgroup.c~cgroup_disable    2008-03-06
>>> 12:19:38.000000000 +0530
>>> +++ linux-2.6.25-rc4-balbir/kernel/cgroup.c    2008-03-06
>>> 12:19:38.000000000 +0530
>>> @@ -782,7 +782,14 @@ static int parse_cgroupfs_options(char *
>>>          if (!*token)
>>>              return -EINVAL;
>>>          if (!strcmp(token, "all")) {
>>> -            opts->subsys_bits = (1 << CGROUP_SUBSYS_COUNT) - 1;
>>> +            /* Add all non-disabled subsystems */
>>> +            int i;
>>> +            opts->subsys_bits = 0;
>>> +            for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>>> +                struct cgroup_subsys *ss = subsys[i];
>>> +                if (!ss->disabled)
>>> +                    opts->subsys_bits |= 1ul << i;
>>> +            }
>>>          } else if (!strcmp(token, "noprefix")) {
>>>              set_bit(ROOT_NOPREFIX, &opts->flags);
>>>          } else if (!strncmp(token, "release_agent=", 14)) {
>>> @@ -800,7 +807,8 @@ static int parse_cgroupfs_options(char *
>>>              for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>>>                  ss = subsys[i];
>>>                  if (!strcmp(token, ss->name)) {
>>> -                    set_bit(i, &opts->subsys_bits);
>>> +                    if (!ss->disabled)
>>> +                        set_bit(i, &opts->subsys_bits);
>>>                      break;
>>>                  }
>>>              }
>>> @@ -2604,6 +2612,8 @@ static int proc_cgroupstats_show(struct     
>>> mutex_lock(&cgroup_mutex);
>>>      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>>>          struct cgroup_subsys *ss = subsys[i];
>>> +        if (ss->disabled)
>>> +            continue;
>>>          seq_printf(m, "%s\t%lu\t%d\n",
>>>                 ss->name, ss->root->subsys_bits,
>>>                 ss->root->number_of_cgroups);
>>> @@ -3010,3 +3020,16 @@ static void cgroup_release_agent(struct     
>>> spin_unlock(&release_list_lock);
>>>      mutex_unlock(&cgroup_mutex);
>>>  }
>>> +
>>> +static int __init cgroup_disable(char *str)
>>> +{
>>> +    int i;
>>> +    for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
>>> +        struct cgroup_subsys *ss = subsys[i];
>>> +        if (!strcmp(str, ss->name)) {
>>> +            ss->disabled = 1;
>>> +            break;
>>> +        }
>>> +    }
>>> +}
>>> +__setup("cgroup_disable=", cgroup_disable);
>>> diff -puN Documentation/kernel-parameters.txt~cgroup_disable
>>> Documentation/kernel-parameters.txt
>>> ---
>>> linux-2.6.25-rc4/Documentation/kernel-parameters.txt~cgroup_disable   
>>> 2008-03-06 17:57:32.000000000 +0530
>>> +++ linux-2.6.25-rc4-balbir/Documentation/kernel-parameters.txt   
>>> 2008-03-06 18:00:32.000000000 +0530
>>> @@ -383,6 +383,10 @@ and is between 256 and 4096 characters.     
>>> ccw_timeout_log [S390]
>>>              See Documentation/s390/CommonIO for details.
>>>  
>>> +    cgroup_disable= [KNL] Enable disable a particular controller
>>> +            Format: {name of the controller}
>>> +            See /proc/cgroups for a list of compiled controllers
>>> +
>> The changelog of this patch:
>> - foo doesn't show up in /proc/cgroups
>>
>> So a disabled subsystem won't show up in /proc/cgroups. In a previous
>> mail, I asked whether it will be useful to print out the disable bit
>> in /proc/cgroups, so we can distinguish a subsystem from disaled and
>> not-compiled.
> 
> Hi, Li,
> 
> That is a good idea, but can that come in later? We need to get the boot option
> in, so that users can decide at boot time whether they want the page_container
> overhead. I'll send out another set of patches to add that feature or work
> with Paul to see what he thinks about it.
> 

I'm not requiring this to be done in this patch. :)

But my exact meaning here is this sentence is confusing:

	See /proc/cgroups for a list of compiled controllers

It seems it is telling people that /proc/cgroups shows not only enabled
but also disabled cgroup subsystems.

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