Re: [Qemu-devel] [PATCH for-4.2 v5 1/2] kvm: s390: split too big memory section on several memslots

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 29 Aug 2019 08:47:49 +0200
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 27.08.19 14:56, Igor Mammedov wrote:
> > On Tue, 20 Aug 2019 18:07:27 +0200
> > Cornelia Huck <cohuck@redhat.com> wrote:
> >   
> >> On Wed,  7 Aug 2019 11:32:41 -0400
> >> Igor Mammedov <imammedo@redhat.com> wrote:
> >>  
> >>> Max memslot size supported by kvm on s390 is 8Tb,
> >>> move logic of splitting RAM in chunks upto 8T to KVM code.
> >>>
> >>> This way it will hide KVM specific restrictions in KVM code
> >>> and won't affect baord level design decisions. Which would allow
> >>> us to avoid misusing memory_region_allocate_system_memory() API
> >>> and eventually use a single hostmem backend for guest RAM.
> >>>
> >>> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> >>> ---
> >>> v5:
> >>>   * move computation 'size -= slot_size' inside of loop body
> >>>           (David Hildenbrand <david@redhat.com>)
> >>> v4:
> >>>   * fix compilation issue
> >>>           (Christian Borntraeger <borntraeger@de.ibm.com>)
> >>>   * advance HVA along with GPA in kvm_set_phys_mem()
> >>>           (Christian Borntraeger <borntraeger@de.ibm.com>)
> >>>
> >>> patch prepares only KVM side for switching to single RAM memory region
> >>> another patch will take care of  dropping manual RAM partitioning in
> >>> s390 code.    
> >>
> >> I may have lost track a bit -- what is the status of this patch (and
> >> the series)?  
> > 
> > Christian,
> > 
> > could you test it on a host that have sufficient amount of RAM?  
> 
> 
> This version looks good. I was able to start a 9TB guest.
> [pid 215723] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=0, flags=0, guest_phys_addr=0, memory_size=8796091973632, userspace_addr=0x3ffee700000}) = 0
> [pid 215723] ioctl(10, KVM_SET_USER_MEMORY_REGION, {slot=1, flags=0, guest_phys_addr=0x7fffff00000, memory_size=1099512676352, userspace_addr=0xbffee600000}) = 0
>
> The only question is if we want to fix the weird alignment (0x7fffff00000) when
> we already add a migration barrier for uber-large guests.
> Maybe we could split at 4TB to avoid future problem with larger page sizes?
That probably should be a separate patch on top.