Re: [PATCH 3/3] mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving

Gregory Price
2024-01-17T05:34:38Z

On Mon, Jan 15, 2024 at 01:47:31PM +0800, Huang, Ying wrote:
> Gregory Price <gourry.memverge@gmail.com> writes:
>
> > + /* Continue allocating from most recent node and adjust the nr_pages */
> > + if (pol->wil.cur_weight) {
> > + node = next_node_in(me->il_prev, nodes);
> > + node_pages = pol->wil.cur_weight;
> > + if (node_pages > rem_pages)
> > + node_pages = rem_pages;
> > + nr_allocated = __alloc_pages_bulk(gfp, node, NULL, node_pages,
> > + NULL, page_array);
... snip ...
> > + if (delta > weight) {
> > + node_pages += weight;
> > + delta -= weight;
> > + } else {
> > + node_pages += delta;
> > + delta = 0;
> > + }
> > + }
> > + nr_allocated = __alloc_pages_bulk(gfp, node, NULL, node_pages,
> > + NULL, page_array);
>
> Should we check nr_allocated here? Allocation may fail anyway.
>

I thought about this briefly in both situations.

If you look at alloc_pages_bulk_array_interleave(), it does not fail if
__alloc_pages_bulk() fails, instead it continues and attempts to
allocate from the remaining nodes.

Presumably, this is because the caller of the bulk allocator can accept
a partial-failure and will go ahead and allocate the remaining pages on
an extra slow path.

Since alloc_pages_bulk_array_interleave() appears to be capable of
failing in the exact same way, I considered this safe.

> > + if (pol->mode == MPOL_WEIGHTED_INTERLEAVE)
> > + return alloc_pages_bulk_array_weighted_interleave(gfp, pol,
> > + nr_pages,
> > + page_array);
> > +
>
> Just nit-pick, may be better to be
>
> return alloc_pages_bulk_array_weighted_interleave(
> gfp, pol, nr_pages, page_array);
>

Wasn't sure on style when names get this long lol, will make the change
:]

Probably v2 thursday or friday

Regards
~Gregory