Re: [PATCH] mm/hugetlb: optionally pre-zero hugetlb pages

[David Hildenbrand <david@redhat.com>]

On 03.12.24 13:06, Michal Hocko wrote:
> On Mon 02-12-24 14:50:49, Frank van der Linden wrote:
>> On Mon, Dec 2, 2024 at 1:58 PM Mateusz Guzik <mjguzik@gmail.com> wrote:
>>> Any games with "background zeroing" are notoriously crappy and I would
>>> argue one should exhaust other avenues before going there -- at the end
>>> of the day the cost of zeroing will have to get paid.
>>
>> I understand that the concept of background prezeroing has been, and
>> will be, met with some resistance. But, do you have any specific
>> concerns with the patch I posted? It's pretty well isolated from the
>> rest of the code, and optional.
> 
> The biggest concern I have is that the overhead is payed by everybody on
> the system - it is considered to be a system overhead regardless only
> part of the workload benefits from hugetlb pages. In other words the
> workload using those pages is not accounted for the use completely.
> 
> If the startup latency is a real problem is there a way to workaround
> that in the userspace by preallocating hugetlb pages ahead of time
> before those VMs are launched and hand over already pre-allocated pages?

In QEMU we support parallel preallocation, and even NUMA-aware 
preallocation, to reduce VM startup times with hugetlb.

We discussed improvements as referred to by Mateusz to further speed up 
preallocation, but for now parallel+NUMA-aware preallocation seems to do 
the trick.

-- 
Cheers,

David / dhildenb