Re: [PATCH] mm/huge_memory: avoid transient none PMDs during lazyfree reclaim

[Lance Yang]

On 2026/10/10 04:44, David Hildenbrand (Arm) wrote:
> On 10/9/26 22:27, Zi Yan wrote:
> > On 9 Oct 2026, at 16:23, David Hildenbrand (Arm) wrote:
> >
> > > On 10/9/26 20:17, Zi Yan wrote:
> > > > There are some gaps we need to close before getting this fix in:
> > > >
> > > > 1. GUP-fast cannot follow the invalidated PMD: riscv and LoongArch need
> > > > pmd_access_permitted() that requires _PAGE_PRESENT; s390's
> > > > pmdp_invalidate() needs a change.
> > >
> > > Ugh. We really need pmdp_invalidate() to have reasonable semantics. This whole
> > > PMD locking is a mess :(
> > >
> > > > 2. sparc64's thp_pte_count can be imbalanced with this change (based on
> > > > Lance's offlist feedback).
> > >
> > > Ack.
> > >
> > > > In addition, powerpc has a page table check issue similr to riscv, where riscv
> > > > fixed it with commit 9f4a88b8d01a6. This is not related to this issue
> > > > but discovered along with the investigation.
> > >
> > > Zi, do you have the capacity to take over this patch?
> >
> > Yes, I can take over it. My plan is to send a series including
> > patches for 1 and this patch as is. powerpc fix can be a separate one.
> >
> > Best Regards,
> > Yan, Zi
>
> If we need a quick stable fix we could temporarily disable the whole thing until
> it is fixed, just a thought.

+1 we could do that for now. A quick fix with minimal churn (correctness 
comes first).