Re: [PATCH v4 4/7] hugetlb: pass *next_nid_to_alloc directly to for_each_node_mask_to_alloc

[Gang Li]

On 2024/1/22 14:16, Muchun Song wrote:
> On 2024/1/18 20:39, Gang Li wrote:
> >   static struct folio *alloc_pool_huge_folio(struct hstate *h,
> >                       nodemask_t *nodes_allowed,
> > -                    nodemask_t *node_alloc_noretry)
> > +                    nodemask_t *node_alloc_noretry,
> > +                    int *next_node)
> >   {
> >       gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
> >       int nr_nodes, node;
> > -    for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
> > +    for_each_node_mask_to_alloc(next_node, nr_nodes, node, 
> > nodes_allowed) {
>
>
> A small question here, why not pass h->next_nid_to_alloc to
> for_each_node_mask_to_alloc()? What's the purpose of the third
> parameter of alloc_pool_huge_folio()?
>
> Thanks.

In hugetlb_alloc_node->alloc_pool_huge_folio, hugetlb is initialized in
parallel at boot time, then it needs each thread to have its own
next_nid, and can't use the global h->next_nid_to_alloc. so an extra 
parameter is added.

And h->next_nid_to_alloc in set_max_huge_pages->alloc_pool_huge_folio
can not be removed. Because if the user calls set_max_huge_pages
frequently and only adds 1 page at a time, that would result in each
request being made on the same node if local variables are used.