Re: [PATCH V3] Add the pagefault count into memcg stats

[Ying Han <yinghan@google.com>]

On Tue, Mar 29, 2011 at 6:16 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
> Hi
>
> sorry, I didn't see past discussion of this thread. then, I may be missing
> something.
>
>> Two new stats in per-memcg memory.stat which tracks the number of
>> page faults and number of major page faults.
>>
>> "pgfault"
>> "pgmajfault"
>>
>> They are different from "pgpgin"/"pgpgout" stat which count number of
>> pages charged/discharged to the cgroup and have no meaning of reading/
>> writing page to disk.
>>
>> It is valuable to track the two stats for both measuring application's
>> performance as well as the efficiency of the kernel page reclaim path.
>> Counting pagefaults per process is useful, but we also need the aggregated
>> value since processes are monitored and controlled in cgroup basis in memcg.
>
> Currently, memory cgroup don't restrict number of page fault. And we already have
> this feature by CONFIG_CGROUP_PERF if my understanding is correct. Why don't you
> use perf cgroup?
>
> In the other words, after your patch, we have four pagefault counter. Do we
> really need *four*? Can't we consolidate them?
>
> 1. tsk->maj_flt
> 2. perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ)
> 3. count_vm_event(PGMAJFAULT);
> 4. mem_cgroup_count_vm_event(PGMAJFAULT);

The first three are per-process and per-system level counters. What I
did in this patch is to add per-memcg counters for pgfault and
pgmajfault. This purpose is not to do any limiting but monitoring. I
am not sure about the CONFIG_CGROUP_PERF, does it require
CONFIG_PERF_EVENTS?

Thanks

--Ying
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