Subject: Re: [PATCH v3 1/7] Basic kernel memory functionality for the Memory Controller

From: Glauber Costa <[email-masked]>
Date: Mon, 26 Sep 2011 20:18:39 -0300

On 09/26/2011 07:34 AM, KAMEZAWA Hiroyuki wrote:
> On Sun, 18 Sep 2011 21:56:39 -0300
> Glauber Costa<[email-masked]>  wrote:
>
>> This patch lays down the foundation for the kernel memory component
>> of the Memory Controller.
>>
>> As of today, I am only laying down the following files:
>>
>>   * memory.independent_kmem_limit
>>   * memory.kmem.limit_in_bytes (currently ignored)
>>   * memory.kmem.usage_in_bytes (always zero)
>>
>> Signed-off-by: Glauber Costa<[email-masked]>
>> CC: Paul Menage<[email-masked]>
>> CC: Greg Thelen<[email-masked]>
>
> I'm sorry that my slow review is delaying you.
>
>
>> ---
>>   Documentation/cgroups/memory.txt |   30 +++++++++-
>>   init/Kconfig                     |   11 ++++
>>   mm/memcontrol.c                  |  115 ++++++++++++++++++++++++++++++++++++--
>>   3 files changed, 148 insertions(+), 8 deletions(-)
>>
>> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
>> index 6f3c598..6f1954a 100644
>> --- a/Documentation/cgroups/memory.txt
>> +++ b/Documentation/cgroups/memory.txt
>> @@ -44,8 +44,9 @@ Features:
>>    - oom-killer disable knob and oom-notifier
>>    - Root cgroup has no limit controls.
>>
>> - Kernel memory and Hugepages are not under control yet. We just manage
>> - pages on LRU. To add more controls, we have to take care of performance.
>> + Hugepages is not under control yet. We just manage pages on LRU. To add more
>> + controls, we have to take care of performance. Kernel memory support is work
>> + in progress, and the current version provides basically functionality.
>>
>>   Brief summary of control files.
>>
>> @@ -56,8 +57,11 @@ Brief summary of control files.
>>   				 (See 5.5 for details)
>>    memory.memsw.usage_in_bytes	 # show current res_counter usage for memory+Swap
>>   				 (See 5.5 for details)
>> + memory.kmem.usage_in_bytes	 # show current res_counter usage for kmem only.
>> +				 (See 2.7 for details)
>>    memory.limit_in_bytes		 # set/show limit of memory usage
>>    memory.memsw.limit_in_bytes	 # set/show limit of memory+Swap usage
>> + memory.kmem.limit_in_bytes	 # if allowed, set/show limit of kernel memory
>>    memory.failcnt			 # show the number of memory usage hits limits
>>    memory.memsw.failcnt		 # show the number of memory+Swap hits limits
>>    memory.max_usage_in_bytes	 # show max memory usage recorded
>> @@ -72,6 +76,9 @@ Brief summary of control files.
>>    memory.oom_control		 # set/show oom controls.
>>    memory.numa_stat		 # show the number of memory usage per numa node
>>
>> + memory.independent_kmem_limit	 # select whether or not kernel memory limits are
>> +				   independent of user limits
>> +
>>   1. History
>>
>>   The memory controller has a long history. A request for comments for the memory
>> @@ -255,6 +262,25 @@ When oom event notifier is registered, event will be delivered.
>>     per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
>>     zone->lru_lock, it has no lock of its own.
>>
>> +2.7 Kernel Memory Extension (CONFIG_CGROUP_MEM_RES_CTLR_KMEM)
>> +
>> + With the Kernel memory extension, the Memory Controller is able to limit
>> +the amount of kernel memory used by the system. Kernel memory is fundamentally
>> +different than user memory, since it can't be swapped out, which makes it
>> +possible to DoS the system by consuming too much of this precious resource.
>> +Kernel memory limits are not imposed for the root cgroup.
>> +
>> +Memory limits as specified by the standard Memory Controller may or may not
>> +take kernel memory into consideration. This is achieved through the file
>> +memory.independent_kmem_limit. A Value different than 0 will allow for kernel
>> +memory to be controlled separately.
>> +
>> +When kernel memory limits are not independent, the limit values set in
>> +memory.kmem files are ignored.
>> +
>> +Currently no soft limit is implemented for kernel memory. It is future work
>> +to trigger slab reclaim when those limits are reached.
>> +
>>   3. User Interface
>>
>>   0. Configuration
>> diff --git a/init/Kconfig b/init/Kconfig
>> index d627783..49e5839 100644
>> --- a/init/Kconfig
>> +++ b/init/Kconfig
>> @@ -689,6 +689,17 @@ config CGROUP_MEM_RES_CTLR_SWAP_ENABLED
>>   	  For those who want to have the feature enabled by default should
>>   	  select this option (if, for some reason, they need to disable it
>>   	  then swapaccount=0 does the trick).
>> +config CGROUP_MEM_RES_CTLR_KMEM
>> +	bool "Memory Resource Controller Kernel Memory accounting"
>> +	depends on CGROUP_MEM_RES_CTLR
>> +	default y
>> +	help
>> +	  The Kernel Memory extension for Memory Resource Controller can limit
>> +	  the amount of memory used by kernel objects in the system. Those are
>> +	  fundamentally different from the entities handled by the standard
>> +	  Memory Controller, which are page-based, and can be swapped. Users of
>> +	  the kmem extension can use it to guarantee that no group of processes
>> +	  will ever exhaust kernel resources alone.
>>
>>   config CGROUP_PERF
>>   	bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index ebd1e86..d32e931 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -73,7 +73,11 @@ static int really_do_swap_account __initdata = 0;
>>   #define do_swap_account		(0)
>>   #endif
>>
>> -
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>> +int do_kmem_account __read_mostly = 1;
>> +#else
>> +#define do_kmem_account		0
>> +#endif
>
>
> Hmm, do we really need this boot option ?
>  From my experience to have swap-accounting boot option,
> this scares us ;) I think config is enough.
>
>
>
>
>>   /*
>>    * Statistics for memory cgroup.
>>    */
>> @@ -270,6 +274,10 @@ struct mem_cgroup {
>>   	 */
>>   	struct res_counter memsw;
>>   	/*
>> +	 * the counter to account for kmem usage.
>> +	 */
>> +	struct res_counter kmem;
>> +	/*
>>   	 * Per cgroup active and inactive list, similar to the
>>   	 * per zone LRU lists.
>>   	 */
>> @@ -321,6 +329,11 @@ struct mem_cgroup {
>>   	 */
>>   	unsigned long 	move_charge_at_immigrate;
>>   	/*
>> +	 * Should kernel memory limits be stabilished independently
>> +	 * from user memory ?
>> +	 */
>> +	int		kmem_independent;
>> +	/*
>>   	 * percpu counter.
>>   	 */
>>   	struct mem_cgroup_stat_cpu *stat;
>> @@ -388,9 +401,14 @@ enum charge_type {
>>   };
>>
>>   /* for encoding cft->private value on file */
>> -#define _MEM			(0)
>> -#define _MEMSWAP		(1)
>> -#define _OOM_TYPE		(2)
>> +
>> +enum mem_type {
>> +	_MEM = 0,
>> +	_MEMSWAP,
>> +	_OOM_TYPE,
>> +	_KMEM,
>> +};
>> +
>
> ok, nice clean up.
>
>
>>   #define MEMFILE_PRIVATE(x, val)	(((x)<<  16) | (val))
>>   #define MEMFILE_TYPE(val)	(((val)>>  16)&  0xffff)
>>   #define MEMFILE_ATTR(val)	((val)&  0xffff)
>> @@ -3943,10 +3961,15 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *mem, bool swap)
>>   	u64 val;
>>
>>   	if (!mem_cgroup_is_root(mem)) {
>> +		val = 0;
>> +		if (!mem->kmem_independent)
>> +			val = res_counter_read_u64(&mem->kmem, RES_USAGE);
>
>>   		if (!swap)
>> -			return res_counter_read_u64(&mem->res, RES_USAGE);
>> +			val += res_counter_read_u64(&mem->res, RES_USAGE);
>>   		else
>> -			return res_counter_read_u64(&mem->memsw, RES_USAGE);
>> +			val += res_counter_read_u64(&mem->memsw, RES_USAGE);
>> +
>> +		return val;
>>   	}
>>
>>   	val = mem_cgroup_recursive_stat(mem, MEM_CGROUP_STAT_CACHE);
>> @@ -3979,6 +4002,10 @@ static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
>>   		else
>>   			val = res_counter_read_u64(&mem->memsw, name);
>>   		break;
>> +	case _KMEM:
>> +		val = res_counter_read_u64(&mem->kmem, name);
>> +		break;
>> +
>>   	default:
>>   		BUG();
>>   		break;
>> @@ -4756,6 +4783,21 @@ static int mem_cgroup_reset_vmscan_stat(struct cgroup *cgrp,
>>   	return 0;
>>   }
>>
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
>> +static u64 kmem_limit_independent_read(struct cgroup *cont, struct cftype *cft)
>> +{
>> +	return mem_cgroup_from_cont(cont)->kmem_independent;
>> +}
>> +
>> +static int kmem_limit_independent_write(struct cgroup *cont, struct cftype *cft,
>> +					u64 val)
>> +{
>> +	cgroup_lock();
>> +	mem_cgroup_from_cont(cont)->kmem_independent = !!val;
>> +	cgroup_unlock();
>
> Hm. This code allows that parent/child can have different settings.
> Could you add parent-child check as..
>
> "If parent sets use_hierarchy==1, children must have the same kmem_independent value
> with parant's one."
>
> How do you think ? I think a hierarchy must have the same config.
BTW, Kame:

Look again (I forgot myself when I first replied to you)
Only in the root cgroup those files get registered.
So shouldn't be a problem, because children won't even
be able to see them.

Do you agree with this ?

>
> BTW...I don't like naming a little ;)
>
> memory->consolidated/shared/?????_kmem_accounting ?
> Or
> memory->kmem_independent_accounting ?
>
> or some better naming ?
>
> Thanks,
> -Kame
>

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