linux-kernel - Re: [RFC][2/3] Account and control virtual address space allocations (v2)

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Date:	Thu, 27 Mar 2008 13:32:21 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Pavel Emelyanov <xemul@...nvz.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hugh@...itas.com>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, lizf@...fujitsu.com,
	linux-kernel@...r.kernel.org, taka@...inux.co.jp,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC][2/3] Account and control virtual address space allocations
 (v2)

Pavel Emelyanov wrote:
> Balbir Singh wrote:
>> Changelog v2
>> ------------
>> Change the accounting to what is already present in the kernel. Split
>> the address space accounting into mem_cgroup_charge_as and
>> mem_cgroup_uncharge_as. At the time of VM expansion, call
>> mem_cgroup_cannot_expand_as to check if the new allocation will push
>> us over the limit
>>
>> This patch implements accounting and control of virtual address space.
>> Accounting is done when the virtual address space of any task/mm_struct
>> belonging to the cgroup is incremented or decremented. This patch
>> fails the expansion if the cgroup goes over its limit.
>>
>> TODOs
>>
>> 1. Only when CONFIG_MMU is enabled, is the virtual address space control
>>    enabled. Should we do this for nommu cases as well? My suspicion is
>>    that we don't have to.
>>
>> Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
>> ---
>>
>>  arch/ia64/kernel/perfmon.c  |    2 +
>>  arch/x86/kernel/ptrace.c    |    7 +++
>>  fs/exec.c                   |    2 +
>>  include/linux/memcontrol.h  |   26 +++++++++++++
>>  include/linux/res_counter.h |   19 ++++++++--
>>  init/Kconfig                |    2 -
>>  kernel/fork.c               |   17 +++++++--
>>  mm/memcontrol.c             |   83 ++++++++++++++++++++++++++++++++++++++++++++
>>  mm/mmap.c                   |   11 +++++
>>  mm/mremap.c                 |    2 +
>>  10 files changed, 163 insertions(+), 8 deletions(-)
>>
>> diff -puN mm/memcontrol.c~memory-controller-virtual-address-space-accounting-and-control mm/memcontrol.c
>> --- linux-2.6.25-rc5/mm/memcontrol.c~memory-controller-virtual-address-space-accounting-and-control	2008-03-26 16:27:59.000000000 +0530
>> +++ linux-2.6.25-rc5-balbir/mm/memcontrol.c	2008-03-27 00:18:16.000000000 +0530
>> @@ -526,6 +526,76 @@ unsigned long mem_cgroup_isolate_pages(u
>>  	return nr_taken;
>>  }
>>  
>> +#ifdef CONFIG_CGROUP_MEM_RES_CTLR_AS
>> +/*
>> + * Charge the address space usage for cgroup. This routine is most
>> + * likely to be called from places that expand the total_vm of a mm_struct.
>> + */
>> +void mem_cgroup_charge_as(struct mm_struct *mm, long nr_pages)
>> +{
>> +	struct mem_cgroup *mem;
>> +
>> +	if (mem_cgroup_subsys.disabled)
>> +		return;
>> +
>> +	rcu_read_lock();
>> +	mem = rcu_dereference(mm->mem_cgroup);
>> +	css_get(&mem->css);
>> +	rcu_read_unlock();
>> +
>> +	res_counter_charge(&mem->as_res, (nr_pages * PAGE_SIZE));
>> +	css_put(&mem->css);
> 
> Why don't you check whether the counter is charged? This is
> bad for two reasons:
> 1. you allow for some growth above the limit (e.g. in expand_stack)

I was doing that earlier and then decided to keep the virtual address space code
in sync with the RLIMIT_AS checking code in the kernel. If you see the flow, it
closely resembles what we do with mm->total_vm and may_expand_vm().
expand_stack() in turn calls acct_stack_growth() which calls may_expand_vm()

> 2. you will undercharge it in the future when uncharging the
>    vme, whose charge was failed and thus unaccounted.

Hmmm...  This should ideally never happen, since we do a may_expand_vm() before
expanding the VM and in our case the virtual address space usage. I've not seen
it during my runs either. But it is something to keep in mind.

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