linux-kernel - Re: [PATCH v7 5/7] mm: Make alloc_contig

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Message-ID: <YHf5bW9GTxeSwfZN@localhost.localdomain>
Date:   Thu, 15 Apr 2021 10:29:33 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Muchun Song <songmuchun@...edance.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 5/7] mm: Make alloc_contig_range handle free hugetlb
 pages

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