Re: [PATCH] mm: migrate: use thp_order instead of HPAGE_PMD_ORDER for new page allocation.

[Andrew Morton]

On Mon,  4 Apr 2022 12:53:25 -0400 Zi Yan <zi.yan@xxxxxxxx> wrote:

> From: Zi Yan <ziy@xxxxxxxxxx>
> 
> With folios support, it is possible to have other than HPAGE_PMD_ORDER
> THPs, in the form of folios, in the system. Use thp_order() to correctly
> determine the source page order during migration.

Changelog doesn't describe the end user visible effects of the bug. 
And it really should, because

> Link: https://lore.kernel.org/linux-mm/20220404132908.GA785673@u2004/

it fixes a kernel crash!