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    SubjectRe: [patch 2/3] memcg: prevent endless loop when charging huge pages to near-limit group
    On Mon, 31 Jan 2011 15:03:54 +0100
    Johannes Weiner <hannes@cmpxchg.org> wrote:

    > +static inline bool res_counter_check_margin(struct res_counter *cnt,
    > + unsigned long bytes)
    > +{
    > + bool ret;
    > + unsigned long flags;
    > +
    > + spin_lock_irqsave(&cnt->lock, flags);
    > + ret = cnt->limit - cnt->usage >= bytes;
    > + spin_unlock_irqrestore(&cnt->lock, flags);
    > + return ret;
    > +}
    > +
    > static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
    > {
    > bool ret;
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index 73ea323..c28072f 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -1111,6 +1111,15 @@ static bool mem_cgroup_check_under_limit(struct mem_cgroup *mem)
    > return false;
    > }
    >
    > +static bool mem_cgroup_check_margin(struct mem_cgroup *mem, unsigned long bytes)
    > +{
    > + if (!res_counter_check_margin(&mem->res, bytes))
    > + return false;
    > + if (do_swap_account && !res_counter_check_margin(&mem->memsw, bytes))
    > + return false;
    > + return true;
    > +}

    argh.

    If you ever have a function with the string "check" in its name, it's a
    good sign that you did something wrong.

    Check what? Against what? Returning what?

    mem_cgroup_check_under_limit() isn't toooo bad - the name tells you
    what's being checked and tells you what to expect the return value to
    mean.

    But "res_counter_check_margin" and "mem_cgroup_check_margin" are just
    awful. Something like

    bool res_counter_may_charge(counter, bytes)

    would be much clearer.

    If we really want to stick with the "check" names (perhaps as an ironic
    reference to res_counter's past mistakes) then please at least document
    the sorry things?



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