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    SubjectRe: [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@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()

    > 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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