linux-kernel - Re: [patch] do_no

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Date:	Mon, 25 Sep 2006 11:31:05 +0200
From:	Jes Sorensen <jes@....com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Linus Torvalds <torvalds@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	bjorn_helgaas@...com, Nick Piggin <nickpiggin@...oo.com.au>,
	Robin Holt <holt@....com>, Dean Nelson <dcn@....com>,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch] do_no_pfn()

Andrew Morton wrote:

> How does this followup look?
> 
> We don't want the rarely-used do_no_pfn() to get inlined in the oft-used
> handle_pte_fault(), using up icache.  Mark it noinline and unlikely.


I'd say it looks good - will give a microscopic slowdown for do_no_pfn
but compared to the overall benefit I think thats more than acceptable.

Acked-by: Jes Sorensen <jes@....com>

Cheers,
Jes

> --- a/mm/memory.c~do_no_pfn-tweaks
> +++ a/mm/memory.c
> @@ -2276,8 +2276,10 @@ oom:
>   *
>   * It is expected that the ->nopfn handler always returns the same pfn
>   * for a given virtual mapping.
> + *
> + * Mark this `noinline' to prevent it from bloating the main pagefault code.
>   */
> -static int do_no_pfn(struct mm_struct *mm, struct vm_area_struct *vma,
> +static noinline int do_no_pfn(struct mm_struct *mm, struct vm_area_struct *vma,
>  		     unsigned long address, pte_t *page_table, pmd_t *pmd,
>  		     int write_access)
>  {
> @@ -2376,7 +2378,7 @@ static inline int handle_pte_fault(struc
>  					return do_no_page(mm, vma, address,
>  							  pte, pmd,
>  							  write_access);
> -				if (vma->vm_ops->nopfn)
> +				if (unlikely(vma->vm_ops->nopfn))
>  					return do_no_pfn(mm, vma, address, pte,
>  							 pmd, write_access);
>  			}
> _

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