On Fri, May 27, 2011 at 1:04 AM, Balbir Singh <balbir@linux.vnet.ibm.com>wrote:

> * Ying Han <yinghan@google.com> [2011-05-26 14:07:49]:
>
> > 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.
> >
>
> inf is a bit confusing for page faults -- no? Why not call it "rest"
> or something line "> 38400".


ok, i can change that to "rest".


> BTW, why was 600 used as base?
>

well, that is based some of my experiments. I am doing anon page allocation
and most of the page fault falls into the bucket of 580 ns - 600 ns. So I
just leave it as default.

However, the bucket is configurable and user can change it based on their
workload and platform.




>
> > 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.
> >
>
> Why not make this per memcg?
>

That can be done.

>
> > 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
>
> Can't we use something like "-1" to mean reset?
>

sounds good to me.

Thank you for reviewing.

--Ying

>
> --
>        Three Cheers,
>        Balbir
>
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