VERY COOL. So Linux has the technology, z/VM has the technology, now it
just takes someo ne to use them.
If anybody in endicott is listening, ONE REQUEST. The current diagnose
used by the CMM function to release a page actually causes z/VM to read
the page in from the paging subsystem before releasing it. So release
100,000 pages that are on the paging subsystem means 100,000 page reads
from disk. VERY BAD. If you discard a page that is on paging disk,
discard it, don't read it and then discard it.
On 12/10/2015 1:38 PM, Christian Borntraeger wrote:
On 12/10/2015 05:58 AM, Alan Altmark wrote:
On Wednesday, 12/09/2015 at 08:15 GMT, Barton Robinson
<bar...@velocitysoftware.com> wrote:
My request to get this fixed was rejected by ibm several years ago. The
problem is that even though linux doesn't have anything on the vdisk,
z/vm still has to back it. I asked for a diagnose as we do with real
storage - a way for Linux to tell z/vm the page no longer needs
backing. So after the swapoff, can you detach the vdisk? That's the
only way with current technology to tell CP to free it up.
The Linux community didn't like the memory state changes we asked for with
CMM, so I don't see why they would assent to the change you describe. A
disk is just another address space that would need the same information.
And there's no such thing as "I'm done" with swapping.
Newer Linux swap code does a discard (TRIM) on the full swap disk
if you do a swapon or on a bunch of pages if a cluster of that swap
disk becomes free. This depends on the parameters of swapon. This was
probably added to improve SSD handling. So if diag 0x250 would gain a
discard capability, something like that would become possible.
Christian
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