Subject: Re: [PATCH] KVM: PPC: BOOK3S: HV: Don't try to allocate from kernel page allocator for hash page table.

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 05 May 2014 20:05:51 +0530

Alexander Graf <[email-masked]> writes:

> On 05/04/2014 07:25 PM, Aneesh Kumar K.V wrote:
>> We reserve 5% of total ram for CMA allocation and not using that can
>> result in us running out of numa node memory with specific
>> configuration. One caveat is we may not have node local hpt with pinned
>> vcpu configuration. But currently libvirt also pins the vcpu to cpuset
>> after creating hash page table.
>
> I don't understand the problem. Can you please elaborate?
>
>

Lets take a system with 100GB RAM. We reserve around 5GB for htab
allocation. Now if we use rest of available memory for hugetlbfs
(because we want all the guest to be backed by huge pages), we would
end up in a situation where we have a few GB of free RAM and 5GB of CMA
reserve area. Now if we allow hash page table allocation to consume the
free space, we would end up hitting page allocation failure for other
non movable kernel allocation even though we still have 5GB CMA reserve
space free.

-aneesh