Re: [PATCH v7 6/7] mm: Make alloc_contig_range handle in-use hugetlb pages

From: Oscar Salvador <osalvador@suse.de>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	David Hildenbrand <david@redhat.com>,
	Michal Hocko <mhocko@kernel.org>,
	Muchun Song <songmuchun@bytedance.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 6/7] mm: Make alloc_contig_range handle in-use hugetlb pages
Date: Wed, 14 Apr 2021 06:52:19 +0200	[thread overview]
Message-ID: <YHZ1A8Wi43DcEv98@localhost.localdomain> (raw)
In-Reply-To: <722f9a5e-ef0a-508a-e58a-6c3eacb5d1bd@oracle.com>

On Tue, Apr 13, 2021 at 03:48:53PM -0700, Mike Kravetz wrote:
> The label free_new is:
> 
> free_new:
>         spin_unlock_irq(&hugetlb_lock);
>         __free_pages(new_page, huge_page_order(h));
> 
>         return ret;
> 
> So, we are locking and immediately unlocking without any code in
> between.  Usually, I don't like like multiple labels before return.
> However, perhaps we should add another to avoid this unnecessary
> cycle.  On the other hand, this is an uncommon race condition so the
> simple code may be acceptable.

I guess we could have something like:

 free_new:
         spin_unlock_irq(&hugetlb_lock);
 free_new_nolock:
         __free_pages(new_page, huge_page_order(h));

         return ret;

And let the retry go to there without locking. But as you said, the
racecondition is rare enough, so I am not sure if this buys us much.
But I can certainly add it if you feel strong about it.

-- 
Oscar Salvador
SUSE L3