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

[David Rientjes <rientjes@google.com>]

On Tue, 29 Mar 2011, Ying Han wrote:

> 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.
> 
> Functional test: check the total number of pgfault/pgmajfault of all
> memcgs and compare with global vmstat value:
> 
> $ cat /proc/vmstat | grep fault
> pgfault 1070751
> pgmajfault 553
> 
> $ cat /dev/cgroup/memory.stat | grep fault
> pgfault 1071138
> pgmajfault 553
> total_pgfault 1071142
> total_pgmajfault 553
> 
> $ cat /dev/cgroup/A/memory.stat | grep fault
> pgfault 199
> pgmajfault 0
> total_pgfault 199
> total_pgmajfault 0
> 
> Performance test: run page fault test(pft) wit 16 thread on faulting in 15G
> anon pages in 16G container. There is no regression noticed on the "flt/cpu/s"
> 
> Sample output from pft:
> TAG pft:anon-sys-default:
>   Gb  Thr CLine   User     System     Wall    flt/cpu/s fault/wsec
>   15   16   1     0.67s   233.41s    14.76s   16798.546 266356.260
> 
> +-------------------------------------------------------------------------+
>     N           Min           Max        Median           Avg        Stddev
> x  10     16682.962     17344.027     16913.524     16928.812      166.5362
> +  10     16695.568     16923.896     16820.604     16824.652     84.816568
> No difference proven at 95.0% confidence
> 
> Change v3..v2
> 1. removed the unnecessary function definition in memcontrol.h
> 
> Signed-off-by: Ying Han <yinghan@google.com>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

I'm wondering if we can just modify count_vm_event() directly for 
CONFIG_CGROUP_MEM_RES_CTLR so that we automatically track all vmstat items 
(those in enum vm_event_item) for each memcg.  We could add an array of 
NR_VM_EVENT_ITEMS into each struct mem_cgroup to be incremented on 
count_vm_event() for current's memcg.

If that's done, we wouldn't have to add additional calls for every vmstat 
item we want to duplicate from the global counters.

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