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    SubjectRe: [PATCH v5 06/14] memcg: kmem controller infrastructure
    On 10/19/2012 01:59 AM, David Rientjes wrote:
    > On Thu, 18 Oct 2012, Glauber Costa wrote:
    >
    >>>> @@ -2630,6 +2634,171 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
    >>>> memcg_check_events(memcg, page);
    >>>> }
    >>>>
    >>>> +#ifdef CONFIG_MEMCG_KMEM
    >>>> +static inline bool memcg_can_account_kmem(struct mem_cgroup *memcg)
    >>>> +{
    >>>> + return !mem_cgroup_disabled() && !mem_cgroup_is_root(memcg) &&
    >>>> + (memcg->kmem_accounted & KMEM_ACCOUNTED_MASK);
    >>>> +}
    >>>> +
    >>>> +static int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp, u64 size)
    >>>> +{
    >>>> + struct res_counter *fail_res;
    >>>> + struct mem_cgroup *_memcg;
    >>>> + int ret = 0;
    >>>> + bool may_oom;
    >>>> +
    >>>> + ret = res_counter_charge(&memcg->kmem, size, &fail_res);
    >>>> + if (ret)
    >>>> + return ret;
    >>>> +
    >>>> + /*
    >>>> + * Conditions under which we can wait for the oom_killer.
    >>>> + * We have to be able to wait, but also, if we can't retry,
    >>>> + * we obviously shouldn't go mess with oom.
    >>>> + */
    >>>> + may_oom = (gfp & __GFP_WAIT) && !(gfp & __GFP_NORETRY);
    >>>
    >>> What about gfp & __GFP_FS?
    >>>
    >>
    >> Do you intend to prevent or allow OOM under that flag? I personally
    >> think that anything that accepts to be OOM-killed should have GFP_WAIT
    >> set, so that ought to be enough.
    >>
    >
    > The oom killer in the page allocator cannot trigger without __GFP_FS
    > because direct reclaim has little chance of being very successful and
    > thus we end up needlessly killing processes, and that tends to happen
    > quite a bit if we dont check for it. Seems like this would also happen
    > with memcg if mem_cgroup_reclaim() has a large probability of failing?
    >

    I can indeed see tests for GFP_FS in some key locations in mm/ before
    calling the OOM Killer.

    Should I test for GFP_IO as well? If the idea is preventing OOM to
    trigger for allocations that can write their pages back, how would you
    feel about the following test:

    may_oom = (gfp & GFP_KERNEL) && !(gfp & __GFP_NORETRY) ?

    Michal, what is your take in here?





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