Re: [PATCH v9 mm-new 03/11] mm: thp: add support for BPF based THP order selection

[David Hildenbrand]

> > I came to the same conclusion. At least it's a valid start.
> >
> > Maybe we would later want a global fallback BPF-THP prog if none was
> > enabled for a specific MM.
>
> good idea. We can fallback to the global model when attaching pid 1.
>
> > But I would expect to start with a per MM way of doing it, it gives you
> > way more flexibility in the long run.
>
> THP, such as shmem and file-backed THP, are shareable across multiple
> processes and cgroups. If we allow different BPF-THP policies to be
> applied to these shared resources, it could lead to policy
> inconsistencies.

Sure, but nothing new about that (e.g., VM_HUGEPAGE, VM_NOHUGEPAGE, 
PR_GET_THP_DISABLE).

I'd expect that we focus on anon THP as the first step either way.

Skimming over this series, anon memory seems to be the main focus.

> This would ultimately recreate a long-standing issue
> in memcg, which still lacks a robust solution for this problem [0].
>
> This suggests that applying SCOPED policies to SHAREABLE memory may be
> fundamentally flawed ;-)

Yeah, shared memory is usually more tricky: see mempolicy handling for 
shmem. There, the policy is much rather glued to a file than to a process.

--
Cheers

David / dhildenb