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    SubjectRe: [RFC][2/3] Account and control virtual address space allocations (v2)
    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)
    2. you will undercharge it in the future when uncharging the
    vme, whose charge was failed and thus unaccounted.


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