This series implements the guest side of a PAPR ACR which allows a
POWER guest's Hashed Page Table (HPT) to be resized at runtime. This
is useful when a guest has a very large theoretical maximum RAM, but
is likely to only ever be expanded to a modest amount of RAM in
practice. Without resizing the HPT has to be sized for the maximum
possible guest RAM, which can be very wasteful if that maximum is
never reached.
To use this requires a hypervisor/host which also supports the PAPR
extension. The only implementation so far is my qemu branch at
https://github.com/dgibson/qemu/tree/upstream/hpt-resize
I expect to merge that code to upstream qemu for qemu-2.9. Note that
HPT resizing will so far only work for TCG guests, KVM support is in
the works. The guest side code here will not require changing for
KVM, however.
An HPT resize can be triggered in one of two ways:
* /sys/kernel/debug/powerpc/pft-size
This debugfs file contains the current size of the HPT (as
encoded in the ibm,pft-size) device tree property. Writing to
it will cause the guest to attempt an HPT resize to the given
value. Note that the current qemu implementation will not
allow the guest to resize the HPT to more than 1/64th of guest
RAM size.
* Automatically on memory hotplug / unplug
With these patches applied, the guest will automatically
attempt to resize its HPT when its RAM size changes due to
hotplug events. (When hot adding RAM qemu considers the new
size for purposes of the limit mentioned above, so this method
can lift the HPT size larger than the former).
David Gibson (6):
kvm: Move KVM_PPC_PVINFO_FLAGS_EV_IDLE definition next to its
structure
powerpc/kvm: Corectly report KVM_CAP_PPC_ALLOC_HTAB
pseries: Add hypercall wrappers for hash page table resizing
pseries: Add support for hash table resizing
pseries: Advertise HPT resizing support via CAS
pseries: Automatically resize HPT for memory hot add/remove
arch/powerpc/include/asm/book3s/64/mmu-hash.h | 1 +
arch/powerpc/include/asm/firmware.h | 5 +-
arch/powerpc/include/asm/hvcall.h | 4 +-
arch/powerpc/include/asm/plpar_wrappers.h | 12 +++
arch/powerpc/include/asm/prom.h | 1 +
arch/powerpc/include/asm/sparsemem.h | 1 +
arch/powerpc/kernel/prom_init.c | 2 +-
arch/powerpc/kvm/powerpc.c | 5 +-
arch/powerpc/mm/hash_utils_64.c | 57 +++++++++++++
arch/powerpc/mm/mem.c | 4 +
arch/powerpc/platforms/pseries/firmware.c | 1 +
arch/powerpc/platforms/pseries/lpar.c | 110 ++++++++++++++++++++++++++
include/uapi/linux/kvm.h | 5 +-
13 files changed, 201 insertions(+), 7 deletions(-)
--
2.9.3
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