Re: [PATCH] KVM: PPC: Book3S HV: increase KVMPPC_NR_LPIDS on POWER8 and POWER9

["Cédric Le Goater" <clg@kaod.org>]

On 7/23/20 8:20 AM, Paul Mackerras wrote:
> On Mon, Jun 08, 2020 at 01:57:14PM +0200, Cédric Le Goater wrote:
>> POWER8 and POWER9 have 12-bit LPIDs. Change LPID_RSVD to support up to
>> (4096 - 2) guests on these processors. POWER7 is kept the same with a
>> limitation of (1024 - 2), but it might be time to drop KVM support for
>> POWER7.
>>
>> Tested with 2048 guests * 4 vCPUs on a witherspoon system with 512G
>> RAM and a bit of swap.
>>
>> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> 
> Thanks, patch applied to my kvm-ppc-next branch.

We have pushed the limits further on a 1TB system and reached the limit
of 4094 guests with 16 vCPUs. 

With more vCPUs, the system starts to check-stop. We believe that the 
pages used by the interrupt controller for the backing store of the 
XIVE internal tables (END and NVT) allocated with GFP_KERNEL are 
reclaimable.

I am thinking of changing the allocation flags with :  
 
	__GFP_NORETRY | __GFP_NOWARN | __GFP_NOMEMALLOC

because XIVE should be able to fail gracefully if the system is 
low on mem. Is that correct ? 

Thanks,  

C.