XEN and es/implementation

[Former Member]

Note 941735 - SAP memory management for 64-bit Linux systems states, that using the std implementation can be used on Linux x86-64 and I heard rumours, that using that memory allocation method is 10 - 15 % faster than mmap.

I remember I read some note, that on a Xen PV instance "map" should be used, that note seems to be vanished (or that sentence)...

Is in that area anything recommended? Is memory disclaiming supported for mmap also?

Markus

[nelis · Accepted solution]

[Note 962334|https://service.sap.com/sap/support/notes/962334] seems to be the central note for Xen but doesn't mention anything regarding es/implementation. Not sure if you've seen it ?

Nelis

[markus_doehr2 · Accepted solution]

Hi Nelis,

yes - I know... I just read "somewhere" that using map is faster than using std - I just can´t remember where... (blog? wiki? Hmm..)

Markus

[nelis · Accepted solution]

Hi Marcus,

I did a quick search through my collection of notes on virtualization and [note 1122388|https://service.sap.com/sap/support/notes/1122388] on VMWare ESX suggests to use 'map' memory model for better memory throughput.

Regards,

Nelis

[markus_doehr2 · Accepted solution]

Thanx - that was the note where I read that!

I wonder if this is true for Xen also (which is a different hypervisor)...

Markus

[hannes_kuehnemund · Accepted solution]

Hi Markus,

since SLES10 SP2 and RHEL5.2, both distributors deliver Xen patches that speed up memory accesses for SAP using es/implementation = std. Since then, the memory performance of Xen is almost at the level of native. Before these version, which means SP1/U1 and older, es/implementation = map was the way to go (with a cap of around 20%). The details on this are on the xen-devel mailing list. Just google for "xen-devel mprotect" and take the first hit.

Best Regards,

Hannes

[markus_doehr2 · Accepted solution]

Hi Hannes,

thanx very much! So memory disclaiming should now also work

Markus