tree 615e8237d74d857d61c41cfa3e778a13c7892a73
parent e673ba9af9bf8fd8e0f44025ac738b8285b3ed27
author Alexey Kardashevskiy <aik@ozlabs.ru> 1505983867 +1000
committer Paolo Bonzini <pbonzini@redhat.com> 1506035211 +0200

memory: Share special empty FlatView

This shares an cached empty FlatView among address spaces. The empty
FV is used every time when a root MR renders into a FV without memory
sections which happens when MR or its children are not enabled or
zero-sized. The empty_view is not NULL to keep the rest of memory
API intact; it also has a dispatch tree for the same reason.

On POWER8 with 255 CPUs, 255 virtio-net, 40 PCI bridges guest this halves
the amount of FlatView's in use (557 -> 260) and dispatch tables
(~800000 -> ~370000).  In an unrelated experiment with 112 non-virtio
devices on x86 ("-M pc"), only 4 FlatViews are alive, and about ~2000
are created at startup.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20170921085110.25598-16-aik@ozlabs.ru>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>