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

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

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);





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