Re: [PATCH v2] mm/fake-numa: fix under-allocation detection in uniform split

[Sang-Heon Jeon <ekffu200098@gmail.com>]

Hi

On Tue, Apr 21, 2026 at 3:29 PM Mike Rapoport <rppt@kernel.org> wrote:
>
> On Mon, Apr 20, 2026 at 11:26:13PM +0900, Sang-Heon Jeon wrote:
> > On Mon, Apr 20, 2026 at 3:31 PM Mike Rapoport <rppt@kernel.org> wrote:
> > > On Fri, Apr 17, 2026 at 10:58:05PM +0900, Sang-Heon Jeon wrote:
> > > > When split NUMA node uniformly, split_nodes_size_interleave_uniform()
> > > > returns the next absolute node ID, not the number of nodes created.
> > > >
> > > > The existing under-allocation detection logic compares next absolute node
> > > > ID (ret) and request count (n), which only works when nid starts at 0.
> > > >
> > > > For example, on a system with 2 physical NUMA nodes (node 0: 2GB, node
> > > > 1: 128MB) and numa=fake=8U, 8 fake nodes are successfully created from
> > > > node 0 and split_nodes_size_interleave_uniform() returns 8. For node 1,
> > > > fake node nid starts at 8, but only 4 fake nodes are created due to
> > > > current FAKE_NODE_MIN_SIZE being 32MB, and
> > > > split_nodes_size_interleave_uniform() returns 12. By existing
> > > > under-allocation detection logic, "ret < n" (12 < 8) is false, so the
> > >
> > > In this example it would be 11, won't it?
> > > I'll update when applying.
> >
> > Oops, my previous reply is not the main point of this review. (Please ignore it)
> > But 12 is still correct, because split_nodes_size_interleave_uniform()
> > returns next available node ID.
> >
> > IMHO, it would be clearer if both the commit message and the function
> > comment change into "next available node ID".
> > If you're okay with it, I'll create v3 patch soon, including minor fix below
>
> No need for v3, I updated the comment and the whitespace:
> https://git.kernel.org/rppt/memblock/c/a34436ac05e76bd6634a89fc0a399ab3a48f509a

Thanks for your help, Mike. However, it seems like '12' was changed to
'11' in the commit message. I think this change should be rolled back.
Could you check?

> > Best Regards,
> > Sang-Heon Jeon
>
> --
> Sincerely yours,
> Mike.

Best Regards,
Sang-Heon Jeon