Messages in this thread | | | Date | Thu, 27 Mar 2008 11:24:35 +0300 | From | Pavel Emelyanov <> | Subject | Re: [RFC][2/3] Account and control virtual address space allocations (v2) |
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Balbir Singh wrote: > 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@linux.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()
But this is racy! Look - you do expand_stack on two CPUs and the limit is almost reached - so that there's room for a single expansion. In this case may_expand_vm will return true for both, since it only checks the limit, while the subsequent charge will fail on one of them, since it actually tries to raise the usage...
>> 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. >
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