On Tue, Mar 10, 2020 at 10:01:21AM +0100, Michal Hocko wrote:
> On Mon 09-03-20 17:25:24, Roman Gushchin wrote:
> [...]
> > 2) Run-time allocations of gigantic hugepages are performed using the
> > cma allocator and the dedicated cma area
>
> [...]
> > @@ -1237,6 +1246,23 @@ static struct page *alloc_gigantic_page(struct hstate *h, gfp_t gfp_mask,
> > {
> > unsigned long nr_pages = 1UL << huge_page_order(h);
> >
> > + if (IS_ENABLED(CONFIG_CMA) && hugetlb_cma[0]) {
> > + struct page *page;
> > + int nid;
> > +
> > + for_each_node_mask(nid, *nodemask) {
> > + if (!hugetlb_cma[nid])
> > + break;
> > +
> > + page = cma_alloc(hugetlb_cma[nid], nr_pages,
> > + huge_page_order(h), true);
> > + if (page)
> > + return page;
> > + }
> > +
> > + return NULL;
>
> Is there any strong reason why the alloaction annot fallback to non-CMA
> allocator when the cma is depleted?
The reason is that that gigantic pages allocated using cma require
a special handling on releasing. It's solvable by using an additional
page flag, but because the current code is usually not working except
a short time just after the system start, I don't think it's worth it.
But I do not have a strong opinion here.
Thanks!
