[gpfsug-discuss] mmap performance against Spectrum Scale

Sven Oehme oehmes at gmail.com
Mon Jan 15 15:00:17 GMT 2018


do you have a repeatable test that runs on just a small number of nodes ?
we where working (still are) on some mmap enhancements lest year, but
didn't get all of them ready for the DCUT of Scale 5.0, so we integrated
only a subset that was ready into Scale 5.0 and left the enhancement turned
off by default (you can toggle it on/off via mmchconfig).
if you are interested in testing this send me a direct mail and i will
provide instructions on how to turn this on.
it does help mmap read workloads significant (think factors) in testing
with synthetic benchmarks in my lab, but i would be very interested in real
application results and also interested to get a trace with the new code to
see where we need to make further improvements.

sven

On Mon, Jan 15, 2018 at 4:26 AM Ray Coetzee <coetzee.ray at gmail.com> wrote:

> Hi Sven
> yes, it's primarily reads.
>
> Kind regards
>
> Ray Coetzee
> Mob: +44 759 704 7060 <+44%207597%20047060>
>
> Skype: ray.coetzee
>
> Email: coetzee.ray at gmail.com
>
>
> On Fri, Jan 12, 2018 at 8:57 PM, Sven Oehme <oehmes at gmail.com> wrote:
>
>> is this primary read or write ?
>>
>>
>> On Fri, Jan 12, 2018, 12:51 PM Ray Coetzee <coetzee.ray at gmail.com> wrote:
>>
>>> Hey Sven, the latest clients I've tested with is 4.2.3-6 on RHEL7.2.
>>> (Without the meltdown patch)
>>>
>>> Hey Bryan, I remember that quote from Yuri, that's why I hoped some
>>> "magic" may have been done since then.
>>>
>>> Other attempts to improve performance I've tried include:
>>>
>>>    - Using LROC to have a larger chance of a cache hit (Unfortunately
>>>    the entire dataset is multiple TB)
>>>    - Built an NVMe based scratch filesystem (18x 1.8TB NVMe) just for
>>>    this purpose (Job runs halved in duration but nowhere near what NFS can
>>>    give)
>>>    - Made changes to prefecthPct, PrefetchAgressiveness, DisableDIO,
>>>    and some others with little improvement.
>>>
>>> For those interested, as a performance comparison. The same job when run
>>> on an aging Isilon takes 1m30s, while GPFS will take ~38min on the all NVMe
>>> scratch filesystem and over 60min on spindle based filesystem.
>>>
>>> Kind regards
>>>
>>> Ray Coetzee
>>> Email: coetzee.ray at gmail.com
>>>
>>>
>>> On Fri, Jan 12, 2018 at 4:12 PM, Bryan Banister <
>>> bbanister at jumptrading.com> wrote:
>>>
>>>> You could put all of your data onto SSDs in a RAID1 configuration so
>>>> that you don’t have insane read-modify-write penalties on writes (RAID1)
>>>> and avoid horrible seek thrashing that spinning rust requires (SSD random
>>>> access medium) for your 4K I/O operations.
>>>>
>>>>
>>>>
>>>> One of my favorite Yuri quotes, “The mmap code is like asbestos… best
>>>> not to touch it”.  He gave many reasons why mmap operations on a
>>>> distributed file system is incredibly hard and not recommended.
>>>>
>>>> -Bryan
>>>>
>>>>
>>>>
>>>> *From:* gpfsug-discuss-bounces at spectrumscale.org [mailto:
>>>> gpfsug-discuss-bounces at spectrumscale.org] *On Behalf Of *Sven Oehme
>>>> *Sent:* Friday, January 12, 2018 8:45 AM
>>>> *To:* coetzee.ray at gmail.com; gpfsug main discussion list <
>>>> gpfsug-discuss at spectrumscale.org>
>>>> *Subject:* Re: [gpfsug-discuss] mmap performance against Spectrum Scale
>>>>
>>>>
>>>>
>>>> *Note: External Email*
>>>> ------------------------------
>>>>
>>>> what version of Scale are you using right now ?
>>>>
>>>>
>>>>
>>>> On Fri, Jan 12, 2018 at 2:29 AM Ray Coetzee <coetzee.ray at gmail.com>
>>>> wrote:
>>>>
>>>> I'd like to ask the group of their experiences in improving the
>>>> performance of applications that use mmap calls against files on Spectrum
>>>> Scale.
>>>>
>>>>
>>>>
>>>> Besides using an NFS export from CES instead of a native GPFS mount, or
>>>> precaching the dataset into the pagepool, what other approaches are there
>>>> to offset the performance hit of the 4K IO size?
>>>>
>>>>
>>>>
>>>> Kind regards
>>>>
>>>> Ray Coetzee
>>>>
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