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

From: Mike Kravetz <mike.kravetz@oracle.com>
To: Oscar Salvador <osalvador@suse.de>
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 10:07:54 -0700	[thread overview]
Message-ID: <681fac27-9684-48cd-daec-fb82057f2253@oracle.com> (raw)
In-Reply-To: <YHZ1A8Wi43DcEv98@localhost.localdomain>

On 4/13/21 9:52 PM, Oscar Salvador wrote:
> 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.

No strong feelings.  I am fine with it as is.

-- 
Mike Kravetz