On 29.04.2016 05:24, David Gibson wrote: > On Tue, Apr 26, 2016 at 04:03:37PM -0500, Michael Roth wrote: ... >> In the case of pseries, the DIMM abstraction isn't really exposed to >> the guest, but rather the memory blocks we use to make the backing >> memdev memory available to the guest. During unplug, the guest >> completely releases these blocks back to QEMU, and if it can only >> release a subset of what's requested it does not attempt to recover. >> We can potentially change that behavior on the guest side, since >> partially-freed DIMMs aren't currently useful on the host-side... >> >> But, in the case of pseries, I wonder if it makes sense to maybe go >> ahead and MADV_DONTNEED the ranges backing these released blocks so the >> host can at least partially reclaim the memory from a partially >> unplugged DIMM? > > Urgh.. I can see the benefit, but I'm a bit uneasy about making the > DIMM semantics different in this way on Power. > > I'm shoehorning the PAPR DR memory mechanism into the qemu DIMM model > was a good idea after all.
Ignorant question (sorry, I really don't have much experience yet here): Could we maybe align the size of the LMBs with the size of the DIMMs? E.g. make the LMBs bigger or the DIMMs smaller, so that they match? Thomas
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