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Message-ID: <20101118125112.GM8135@csn.ul.ie>
Date: Thu, 18 Nov 2010 12:51:12 +0000
From: Mel Gorman <mel@....ul.ie>
To: Andrea Arcangeli <aarcange@...hat.com>
Cc: linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Marcelo Tosatti <mtosatti@...hat.com>,
Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
Hugh Dickins <hugh.dickins@...cali.co.uk>,
Rik van Riel <riel@...hat.com>,
Dave Hansen <dave@...ux.vnet.ibm.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Ingo Molnar <mingo@...e.hu>, Mike Travis <travis@....com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Christoph Lameter <cl@...ux-foundation.org>,
Chris Wright <chrisw@...s-sol.org>, bpicco@...hat.com,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Johannes Weiner <hannes@...xchg.org>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Chris Mason <chris.mason@...cle.com>,
Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 16 of 66] special pmd_trans_* functions
On Wed, Nov 03, 2010 at 04:27:51PM +0100, Andrea Arcangeli wrote:
> From: Andrea Arcangeli <aarcange@...hat.com>
>
> These returns 0 at compile time when the config option is disabled, to allow
> gcc to eliminate the transparent hugepage function calls at compile time
> without additional #ifdefs (only the export of those functions have to be
> visible to gcc but they won't be required at link time and huge_memory.o can be
> not built at all).
>
> _PAGE_BIT_UNUSED1 is never used for pmd, only on pte.
>
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> Acked-by: Rik van Riel <riel@...hat.com>
> ---
>
> diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
> --- a/arch/x86/include/asm/pgtable_64.h
> +++ b/arch/x86/include/asm/pgtable_64.h
> @@ -168,6 +168,19 @@ extern void cleanup_highmap(void);
> #define kc_offset_to_vaddr(o) ((o) | ~__VIRTUAL_MASK)
>
> #define __HAVE_ARCH_PTE_SAME
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static inline int pmd_trans_splitting(pmd_t pmd)
> +{
> + return pmd_val(pmd) & _PAGE_SPLITTING;
> +}
> +
> +static inline int pmd_trans_huge(pmd_t pmd)
> +{
> + return pmd_val(pmd) & _PAGE_PSE;
> +}
> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> +
> #endif /* !__ASSEMBLY__ */
>
> #endif /* _ASM_X86_PGTABLE_64_H */
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -22,6 +22,7 @@
> #define _PAGE_BIT_PAT_LARGE 12 /* On 2MB or 1GB pages */
> #define _PAGE_BIT_SPECIAL _PAGE_BIT_UNUSED1
> #define _PAGE_BIT_CPA_TEST _PAGE_BIT_UNUSED1
> +#define _PAGE_BIT_SPLITTING _PAGE_BIT_UNUSED1 /* only valid on a PSE pmd */
> #define _PAGE_BIT_NX 63 /* No execute: only valid after cpuid check */
>
> /* If _PAGE_BIT_PRESENT is clear, we use these: */
> @@ -45,6 +46,7 @@
> #define _PAGE_PAT_LARGE (_AT(pteval_t, 1) << _PAGE_BIT_PAT_LARGE)
> #define _PAGE_SPECIAL (_AT(pteval_t, 1) << _PAGE_BIT_SPECIAL)
> #define _PAGE_CPA_TEST (_AT(pteval_t, 1) << _PAGE_BIT_CPA_TEST)
> +#define _PAGE_SPLITTING (_AT(pteval_t, 1) << _PAGE_BIT_SPLITTING)
> #define __HAVE_ARCH_PTE_SPECIAL
>
> #ifdef CONFIG_KMEMCHECK
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -348,6 +348,11 @@ extern void untrack_pfn_vma(struct vm_ar
> unsigned long size);
> #endif
>
> +#ifndef CONFIG_TRANSPARENT_HUGEPAGE
> +#define pmd_trans_huge(pmd) 0
> +#define pmd_trans_splitting(pmd) 0
> +#endif
> +
Usually it is insisted upon that this looks like
static inline int pmd_trans_huge(pmd) {
return 0;
}
I understand it's to avoid any possibility of side-effets though to have type
checking and I am 99% certain the compiler still does the right thing. Still,
with no obvious side-effects here;
Acked-by: Mel Gorman <mel@....ul.ie>
> #endif /* !__ASSEMBLY__ */
>
> #endif /* _ASM_GENERIC_PGTABLE_H */
>
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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