RFR(M): 8171181: Supporting heap allocation on alternative memory devices

[Kharbas, Kishor]

Hi Andrew!

> -----Original Message-----
> From: Andrew Haley [mailto:aph at redhat.com]
> Sent: Friday, March 3, 2017 1:21 AM
> To: Kharbas, Kishor <kishor.kharbas at intel.com>; hotspot-runtime-
> dev at openjdk.java.net
> Subject: Re: RFR(M): 8171181: Supporting heap allocation on alternative
> memory devices
> 
> On 03/03/17 03:32, Kharbas, Kishor wrote:
> 
> > The JEP is not DAX specific, but the implementation is.
> > Do you have any ideas on how we can check whether NUMA is supported
> by
> > the underlying filesystem?
> 
> What are the consequences if it isn't?  All that this patch does (as far as I can
> see) is allow the heap to be allocated in a file in a named directory. 

Yes that's right, it just allocates heap in a file in the given directory. My understanding is that this flag will be used by advanced Java users who would understand that they need to specify a DAX or a special directory to access the new memory.

 So, will
> there be failures if the system does support NUMA but the DAX filesystem
> doesn't?

I don't think there will be failures if that happens. The user needs to be let known that NUMA is not supported if he tries to use NUMA in conjunction to this flag.

> 
> Andrew.