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

[Oscar Salvador <osalvador@suse.de>]

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