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Re: [Qemu-ppc] [Qemu-devel] [RFC PATCH v0 0/2] Increase max memslots to
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [Qemu-devel] [RFC PATCH v0 0/2] Increase max memslots to 512 for PowerPC |
Date: |
Fri, 3 Jun 2016 11:14:42 +1000 |
User-agent: |
Mutt/1.6.1 (2016-04-27) |
On Thu, Jun 02, 2016 at 07:37:37PM +0530, Bharata B Rao wrote:
> On Thu, Jun 02, 2016 at 09:03:15AM +0200, Thomas Huth wrote:
> > On 02.06.2016 06:39, Bharata B Rao wrote:
> > ...
> > > Agreed. Here is the updated patch:
> > >
> > > spapr: Increase hotpluggable memory slots to 256
> > >
> > > From: Bharata B Rao <address@hidden>
> > >
> > > KVM now supports 512 memslots on PowerPC (earlier it was 32). Allow half
> > > of it (256) to be used as hotpluggable memory slots.
> > >
> > > Instead of hard coding the max value, use the KVM supplied value if KVM
> > > is enabled. Otherwise resort to the default value of 32.
> > >
> > > Signed-off-by: Bharata B Rao <address@hidden>
> > > ---
> > > hw/ppc/spapr.c | 15 +++++++++++++--
> > > 1 file changed, 13 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > > index 44e401a..c82adef 100644
> > > --- a/hw/ppc/spapr.c
> > > +++ b/hw/ppc/spapr.c
> > > @@ -1816,11 +1816,22 @@ static void ppc_spapr_init(MachineState *machine)
> > > /* initialize hotplug memory address space */
> > > if (machine->ram_size < machine->maxram_size) {
> > > ram_addr_t hotplug_mem_size = machine->maxram_size -
> > > machine->ram_size;
> > > + /*
> > > + * Number of memslots supported by KVM on PowerPC was increased
> > > + * from 32 to 512. Let us limit the number of hotpluggable slots
> > > + * to half of that (256). However ensure that number of slots
> > > + * doesn't drop below 32 on older hosts.
> > > + */
> >
> > Using "hard-coded" information like "increased to 512" in comments is
> > true for the current state, but this has a risk of being out of date
> > soon. Once we change the memslots in the kernel, this comment is not
> > true anymore and might cause confusion. Better talk about leaving half
> > of the kernel memslots for PCI and other devices, or so.
>
> Just want to note that even though we are limiting hotpluggable memory
> slots to half of max, it is always possible for other devices to eat
> into the memory hotplug slots, right ?
>
> David - here is the patch updated with comments as suggested by Thomas.
> If you need a separate post, let me know.
Applied to ppc-for-2.7, thanks.
>
> spapr: Increase hotpluggable memory slots to 256
>
> From: Bharata B Rao <address@hidden>
>
> KVM now supports 512 memslots on PowerPC (earlier it was 32). Allow half
> of it (256) to be used as hotpluggable memory slots.
>
> Instead of hard coding the max value, use the KVM supplied value if KVM
> is enabled. Otherwise resort to the default value of 32.
>
> Signed-off-by: Bharata B Rao <address@hidden>
> Reviewed-by: Thomas Huth <address@hidden>
> ---
> hw/ppc/spapr.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 44e401a..14cc6ae 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1816,11 +1816,21 @@ static void ppc_spapr_init(MachineState *machine)
> /* initialize hotplug memory address space */
> if (machine->ram_size < machine->maxram_size) {
> ram_addr_t hotplug_mem_size = machine->maxram_size -
> machine->ram_size;
> + /*
> + * Limit the number of hotpluggable memory slots to half the number
> + * slots that KVM supports, leaving the other half for PCI and other
> + * devices. However ensure that number of slots doesn't drop below
> 32.
> + */
> + int max_memslots = kvm_enabled() ? kvm_get_max_memslots() / 2 :
> + SPAPR_MAX_RAM_SLOTS;
>
> - if (machine->ram_slots > SPAPR_MAX_RAM_SLOTS) {
> + if (max_memslots < SPAPR_MAX_RAM_SLOTS) {
> + max_memslots = SPAPR_MAX_RAM_SLOTS;
> + }
> + if (machine->ram_slots > max_memslots) {
> error_report("Specified number of memory slots %"
> PRIu64" exceeds max supported %d",
> - machine->ram_slots, SPAPR_MAX_RAM_SLOTS);
> + machine->ram_slots, max_memslots);
> exit(1);
> }
>
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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