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

Alexander Graf agraf at suse.de
Tue May 6 01:16:05 EST 2014

> Am 05.05.2014 um 16:35 schrieb "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>:
> Alexander Graf <agraf at suse.de> 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.

Isn't this a greater problem? We should start swapping before we hit the point where non movable kernel allocation fails, no?

The fact that KVM uses a good number of normal kernel pages is maybe suboptimal, but shouldn't be a critical problem.


> -aneesh

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