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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