Re: [PATCH] memcg: add pgfault latency histograms

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Thu, 26 May 2011 14:07:49 -0700
Ying Han <yinghan@google.com> wrote:

> This adds histogram to capture pagefault latencies on per-memcg basis. I used
> this patch on the memcg background reclaim test, and figured there could be more
> usecases to monitor/debug application performance.
> 
> The histogram is composed 8 bucket in ns unit. The last one is infinite (inf)
> which is everything beyond the last one. To be more flexible, the buckets can
> be reset and also each bucket is configurable at runtime.
> 
> memory.pgfault_histogram: exports the histogram on per-memcg basis and also can
> be reset by echoing "reset". Meantime, all the buckets are writable by echoing
> the range into the API. see the example below.
> 
> /proc/sys/vm/pgfault_histogram: the global sysfs tunablecan be used to turn
> on/off recording the histogram.
> 
> Functional Test:
> Create a memcg with 10g hard_limit, running dd & allocate 8g anon page.
> Measure the anon page allocation latency.
> 
> $ mkdir /dev/cgroup/memory/B
> $ echo 10g >/dev/cgroup/memory/B/memory.limit_in_bytes
> $ echo $$ >/dev/cgroup/memory/B/tasks
> $ dd if=/dev/zero of=/export/hdc3/dd/tf0 bs=1024 count=20971520 &
> $ allocate 8g anon pages
> 
> $ echo 1 >/proc/sys/vm/pgfault_histogram
> 
> $ cat /dev/cgroup/memory/B/memory.pgfault_histogram
> pgfault latency histogram (ns):
> < 600            2051273
> < 1200           40859
> < 2400           4004
> < 4800           1605
> < 9600           170
> < 19200          82
> < 38400          6
> < inf            0
> 
> $ echo reset >/dev/cgroup/memory/B/memory.pgfault_histogram
> $ cat /dev/cgroup/memory/B/memory.pgfault_histogram
> pgfault latency histogram (ns):
> < 600            0
> < 1200           0
> < 2400           0
> < 4800           0
> < 9600           0
> < 19200          0
> < 38400          0
> < inf            0
> 
> $ echo 500 520 540 580 600 1000 5000 >/dev/cgroup/memory/B/memory.pgfault_histogram
> $ cat /dev/cgroup/memory/B/memory.pgfault_histogram
> pgfault latency histogram (ns):
> < 500            50
> < 520            151
> < 540            3715
> < 580            1859812
> < 600            202241
> < 1000           25394
> < 5000           5875
> < inf            186
> 
> Performance Test:
> I ran through the PageFaultTest (pft) benchmark to measure the overhead of
> recording the histogram. There is no overhead observed on both "flt/cpu/s"
> and "fault/wsec".
> 
> $ mkdir /dev/cgroup/memory/A
> $ echo 16g >/dev/cgroup/memory/A/memory.limit_in_bytes
> $ echo $$ >/dev/cgroup/memory/A/tasks
> $ ./pft -m 15g -t 8 -T a
> 
> Result:
> "fault/wsec"
> 
> $ ./ministat no_histogram histogram
> x no_histogram
> + histogram
> +--------------------------------------------------------------------------+
>    N           Min           Max        Median           Avg        Stddev
> x   5     813404.51     824574.98      821661.3     820470.83     4202.0758
> +   5     821228.91     825894.66     822874.65     823374.15     1787.9355
> 
> "flt/cpu/s"
> 
> $ ./ministat no_histogram histogram
> x no_histogram
> + histogram
> +--------------------------------------------------------------------------+
>    N           Min           Max        Median           Avg        Stddev
> x   5     104951.93     106173.13     105142.73      105349.2     513.78158
> +   5     104697.67      105416.1     104943.52     104973.77     269.24781
> No difference proven at 95.0% confidence
> 
> Signed-off-by: Ying Han <yinghan@google.com>

Hmm, interesting....but isn't it very very very complicated interface ?
Could you make this for 'perf' ? Then, everyone (including someone who don't use memcg)
will be happy.
Thanks,
-Kame


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