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

[Balbir Singh <balbir@linux.vnet.ibm.com>]

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.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL