On Wed, 25 Sep 2019 11:27:00 +0800 Peter Xu <pet...@redhat.com> wrote:
> On Tue, Sep 24, 2019 at 10:47:51AM -0400, Igor Mammedov wrote: > > s390 was trying to solve limited KVM memslot size issue by abusing > > memory_region_allocate_system_memory(), which breaks API contract > > where the function might be called only once. > > > > Beside an invalid use of API, the approach also introduced migration > > issue, since RAM chunks for each KVM_SLOT_MAX_BYTES are transferred in > > migration stream as separate RAMBlocks. > > > > After discussion [1], it was agreed to break migration from older > > QEMU for guest with RAM >8Tb (as it was relatively new (since 2.12) > > and considered to be not actually used downstream). > > Migration should keep working for guests with less than 8TB and for > > more than 8TB with QEMU 4.2 and newer binary. > > In case user tries to migrate more than 8TB guest, between incompatible > > QEMU versions, migration should fail gracefully due to non-exiting > > RAMBlock ID or RAMBlock size mismatch. > > > > Taking in account above and that now KVM code is able to split too > > big MemorySection into several memslots, partially revert commit > > (bb223055b s390-ccw-virtio: allow for systems larger that 7.999TB) > > and use kvm_set_max_memslot_size() to set KVMSlot size to > > KVM_SLOT_MAX_BYTES. > > > > 1) [PATCH RFC v2 4/4] s390: do not call > > memory_region_allocate_system_memory() multiple times > > > > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > > Acked-by: Peter Xu <pet...@redhat.com> > > IMHO it would be good to at least mention bb223055b9 in the commit > message even if not with a "Fixed:" tag. May be amended during commit > if anyone prefers. /me confused, bb223055b9 is mentioned in commit message > Also, this only applies the split limitation to s390. Would that be a > good thing to some other archs as well? Don't we have the similar bitmap size issue in KVM for other archs? > > Thanks, >
