Re: [LKP] [mm] ac5b2c1891: vm-scalability.throughput -61.3% regression

[Linus Torvalds]

On Tue, Nov 27, 2018 at 12:57 PM Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote:
>
> This difference can only happen with defrag=always, and that's not the
> current upstream default.

Ok, thanks. That makes it a bit less critical.

> That MADV_HUGEPAGE causes flights with NUMA balancing is not great
> indeed, qemu needs NUMA locality too, but then the badness caused by
> __GFP_THISNODE was a larger regression in the worst case for qemu.
[...]
> So the short term alternative again would be the alternate patch that
> does __GFP_THISNODE|GFP_ONLY_COMPACT appended below.

Sounds like we should probably do this. Particularly since Vlastimil
pointed out that we'd otherwise have issues with the back-port for 4.4
where that "defrag=always" was the default.

The patch doesn't look horrible, and it directly addresses this
particular issue.

Is there some reason we wouldn't want to do it?

               Linus