Re: [PATCH v8 14/14] mm: thp: always enable mTHP support

[Luiz Capitulino]

On 10/2/26 11:13 PM, Lance Yang wrote:
> On Thu, Sep 17, 2026 at 09:45:35PM -0400, Luiz Capitulino wrote:
> > If PMD-sized pages are not supported on an architecture (ie. the
> > arch implements arch_has_pmd_leaves() and it returns false) then the
> > current code disables all THP, including mTHP.
> >
> > This commit fixes this by allowing mTHP to be always enabled for all
> > archs. When PMD-sized pages are not supported, its sysfs entry won't be
> > created and their mapping will be disallowed at page-fault time.
> >
> > Similarly, this commit implements the following changes for shmem in
> > shmem_allowable_huge_orders():
> >
> > - Drop the pgtable_has_pmd_leaves() check so that mTHP sizes are
> >    considered
> > - Filter out PMD and PUD orders from allowable orders when
> >    PMD-sized pages are not supported by the CPU
>
> Nit: "and PUD" can go.
>
> David mentioned
>
> "
> There is no need to disable PUD-orders, as shmem does not support PUD-orders
> (unlike DAX). So you can keep it simpler here.
> "
>
> in v4
>
> https://lore.kernel.org/all/ff7bcd65-d444-4da1-890e-75504303ec3f@xxxxxxxxxx/

Yes, I changed the code and didn't update the changelog. Fixed now,
thanks Lance.

> Cheers, Lance