distributed shared memory / mmap

distributed shared memory / mmap

[Martin Uecker]

Hi!

Is there any easy way to get shared memory between to
processes on different machines? It seems possible using mmap
on a file system like GFS on top of a distributed block device.


Sincerly,
Martin Uecker

Re: distributed shared memory / mmap

[Steven Whitehouse]

Hi,

On Wed, 2008-08-20 at 15:18 +0200, Martin Uecker wrote:
> 
> Hi!
> 
> Is there any easy way to get shared memory between to
> processes on different machines? It seems possible using mmap
> on a file system like GFS on top of a distributed block device.
> 
> 
> Sincerly,
> Martin Uecker
> 
Yes, you can do it using GFS/GFS2 and it should work. On the other hand,
don't do it. Its probably not what you want and unlikely to give you
good performance since the locking is "per inode" and thus you'll
generate a lot of cache flushing if there is any appreciable amount of
writing to the shared region. If you have a read mostly (or only)
workload, then it will work much better.

There are often better solutions though, depending on the application in
question,

Steve.

Re: distributed shared memory / mmap

[Louis Rilling]

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On Wed, Aug 20, 2008 at 03:43:24PM +0100, Steven Whitehouse wrote:
> Hi,
> 
> On Wed, 2008-08-20 at 15:18 +0200, Martin Uecker wrote:
> > 
> > Hi!
> > 
> > Is there any easy way to get shared memory between to
> > processes on different machines? It seems possible using mmap
> > on a file system like GFS on top of a distributed block device.
> > 
> > 
> > Sincerly,
> > Martin Uecker
> > 
> Yes, you can do it using GFS/GFS2 and it should work. On the other hand,
> don't do it. Its probably not what you want and unlikely to give you
> good performance since the locking is "per inode" and thus you'll
> generate a lot of cache flushing if there is any appreciable amount of
> writing to the shared region. If you have a read mostly (or only)
> workload, then it will work much better.

Alternatively, you can use kernel-level DSM like provided by Kerrighed.
Kerrighed provides cluster-wide SYSV shm segments, which sharing is handled
at the page level -> far better than the inode level.

You may find this solution not-so-easy though...

Regards,

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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Re: distributed shared memory / mmap

[Mark Hounschell]

Martin Uecker wrote:
> 
> Hi!
> 
> Is there any easy way to get shared memory between to
> processes on different machines? It seems possible using mmap
> on a file system like GFS on top of a distributed block device.
> 
> 

There is hardware available, designed just for this. Reflective Memory 
pci cards.

Mark

Re: distributed shared memory / mmap

[linux-os (Dick Johnson)]

On Wed, 20 Aug 2008, Mark Hounschell wrote:

> Martin Uecker wrote:
>>
>> Hi!
>>
>> Is there any easy way to get shared memory between to
>> processes on different machines? It seems possible using mmap
>> on a file system like GFS on top of a distributed block device.
>>
>>
>
> There is hardware available, designed just for this. Reflective Memory
> pci cards.
>
> Mark
> --

Check out "Fabric." There is even an InfiniBand driver in the
kernel. Fabric attached memory is used for HPC (High Performance
Computing). It's been around for a couple of years and is fairly
mature.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.22.1 on an i686 machine (4785.87 BogoMips).
My book : http://www.AbominableFirebug.com/
_


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