linux-kernel - Re: [PATCH v7 6/7] mm: Make alloc_contig

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Date:   Wed, 14 Apr 2021 10:07:54 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Muchun Song <songmuchun@...edance.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 6/7] mm: Make alloc_contig_range handle in-use hugetlb
 pages

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