Re: [PATCH v3 05/28] mm/hugetlb: fix round-robin bootmem allocation

[Frank van der Linden <fvdl@google.com>]

On Mon, Feb 10, 2025 at 4:57 AM Oscar Salvador <osalvador@suse.de> wrote:
>
> On Thu, Feb 06, 2025 at 06:50:45PM +0000, Frank van der Linden wrote:
> > Commit b5389086ad7b ("hugetlbfs: extend the definition of hugepages parameter to support node allocation")
> > changed the NUMA_NO_NODE round-robin allocation behavior in case of a
> > failure to allocate from one NUMA node. The code originally moved on to
> > the next node to try again, but now it immediately breaks out of the loop.
> >
> > Restore the original behavior.
>
> Did you stumble upon this?
>
> AFAICS, memblock_alloc_range_nid() will call memblock_find_in_range_node() with
> NUMA_NO_NODE for exact_nide = false, which would be our case.
> Meaning that if memblock_alloc_try_nid_raw() returns false here, it is because
> we could not allocate the page in any node, right?

Hmm.. this patch is from earlier in the development when I stumbled on
a situation that looked like I describe it. However, you're right,
there is really no point to this patch. I mean, it's harmless in the
sense that it doesn't cause bugs, but it just wastes time. The problem
I saw might just have been caused by my own changes at the time, which
have been re-arranged since. I was probably also confused by the
for_each, which isn't really a for loop the way that it's used in this
function.

Looking at it further, it's actually the node-specific case that is
wrong. That case also uses memblock_alloc_try_nid_raw(), but it should
be using memblock_alloc_exact_nid_raw(). Right now, if you do e.g.
hugepages=0:X,1:Y, and there aren't X pages available on node 0, it
will still fall back to node 1, which is unexpected/unwanted behavior.

So, I'll change this patch to fix the node-specific case instead.
Looking at it, I also need to avoid the same fallback for the CMA
case, which will affect those patches a bit.

So, there'll be a v4 coming up. Fortunately, it won't affect the
patches with your Reviewed-by, so thanks again for those.

- Frank