Re: [PATCH v7 5/7] mm: Make alloc_contig_range handle free hugetlb pages

[Oscar Salvador <osalvador@suse.de>]

On Tue, Apr 13, 2021 at 03:40:18PM +0200, Michal Hocko wrote:
> > +		/*
> > +		 * Call __prep_new_huge_page() to construct the hugetlb page, and
> > +		 * enqueue it then to place it in the freelists. After this,
> > +		 * counters are back on track. Free hugepages have a refcount of 0,
> > +		 * so we need to decrease new_page's count as well.
> > +		 */
> > +		__prep_new_huge_page(new_page);
> > +		__prep_account_new_huge_page(h, nid);
> 
> I think it would help to put something like the following into the
> comment above this really strange construct.
> 
> 		/*
> 		 * new_page needs to be initialized with the standard
> 		 * hugetlb state. This is normally done by
> 		 * prep_new_huge_page but that takes hugetlb_lock which
> 		 * is already held so we need to open code it here.
> 		 * Reference count trick is needed because allocator
> 		 * gives us referenced page but the pool requires pages
> 		 * with 0 refcount.
> 		 */

Ok, I will try to add more info, thanks Michal!

-- 
Oscar Salvador
SUSE L3