Rob van der Heij wrote:
On Wed, Jul 8, 2009 at 1:26 AM, Ivan Warren<i...@vmfacility.fr> wrote:What I am saying is that, on the contrary, when linux treats those pages as no longer being in use, z/VM *WILL* see them as free !I think you have read too much glossy marketing PDFs :-) All we know is that VM *could* see it as free and we know it's not always looking for it at that place. And in fact, in this case Holy Page Management Assist is likely to do the thing. I second Mark that CMM-1 is the thing immediately frees the backing pages in z/VM. I use it on my test servers to reduce the footprint when I am done with my tests. It's not true that CMM-1 involves another virtual machine to do that (only if you choose to use VMRM to steer CMM).
I haven't read any of the (glossy or not) marketing PDFs ! I'm reading the linux 2.6 source code and the z/VM CP System services manuals. cmm-1 (arch/s390/mm/cmm.c) uses SMSGs to communicate with the VMRM service virtual machine. The VMRM will instruct the guest to release its pages using good ole Diag 10.. nothing fancy here.. cmma (arch/s390/mm/page_states.c) uses the B9AB instruction to indicate to CP which pages linux no longer needs.. It uses the standard Linux MM mechanism to be instructed to do so. (page_free()).. The only diff between Diag 10 and B9AB is that a page marked "Unused" with B9AB will generate an Addressing Exception (PIC 5) if you attempt to access it, while Diag 10 won't do that. Ok.. maybe I'm confusing the terminology.. but that's what's in the linux source code.. --Ivan ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
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