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Date: Tue, 19 Feb 2013 11:37:30 -0800 (PST)
From: David Rientjes <rientjes@google.com>
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To: David Miller <davem@davemloft.net>
cc: mroos@ut.ee, linux-mm@vger.kernel.org, linux-kernel@vger.kernel.org,
        sparclinux@vger.kernel.org
Subject: Re: THP bug and crash on sparc64 3.8
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On Tue, 19 Feb 2013, David Miller wrote:

> diff --git a/arch/sparc/mm/tsb.c b/arch/sparc/mm/tsb.c
> index 7f64743..338b406 100644
> --- a/arch/sparc/mm/tsb.c
> +++ b/arch/sparc/mm/tsb.c
> @@ -288,14 +288,13 @@ static unsigned long tsb_size_to_rss_limit(unsigned long new_size)
>   * the number of entries that the current TSB can hold at once.  Currently,
>   * we trigger when the RSS hits 3/4 of the TSB capacity.
>   */
> -void tsb_grow(struct mm_struct *mm, unsigned long tsb_index, unsigned long rss)
> +void tsb_grow(struct mm_struct *mm, unsigned long tsb_index, unsigned long rss, gfp_t gfp)
>  {
>  	unsigned long max_tsb_size = 1 * 1024 * 1024;
>  	unsigned long new_size, old_size, flags;
>  	struct tsb *old_tsb, *new_tsb;
>  	unsigned long new_cache_index, old_cache_index;
>  	unsigned long new_rss_limit;
> -	gfp_t gfp_flags;
>  
>  	if (max_tsb_size > (PAGE_SIZE << MAX_ORDER))
>  		max_tsb_size = (PAGE_SIZE << MAX_ORDER);
> @@ -312,12 +311,11 @@ void tsb_grow(struct mm_struct *mm, unsigned long tsb_index, unsigned long rss)
>  		new_rss_limit = ~0UL;
>  
>  retry_tsb_alloc:
> -	gfp_flags = GFP_KERNEL;
>  	if (new_size > (PAGE_SIZE * 2))
> -		gfp_flags = __GFP_NOWARN | __GFP_NORETRY;
> +		gfp = __GFP_NOWARN | __GFP_NORETRY;

The existing code here already looks buggy for a different reason, it 
should be gfp |= __GFP_NOWARN | __GFP_NORETRY;

I was wondering if you could get away with just a simple one-liner fix 
above by doing

	gfp_flags = rss ? GFP_KERNEL : GFP_NOWAIT;

but I agree this is more robust.