linux-kernel - Re: [PATCH 13 of 66] export maybe

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Date:	Mon, 17 Jan 2011 15:14:07 +0100
From:	Michal Simek <michal.simek@...alogix.com>
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>, Mel Gorman <mel@....ul.ie>,
	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 13 of 66] export maybe_mkwrite

Andrea Arcangeli wrote:
> From: Andrea Arcangeli <aarcange@...hat.com>
> 
> huge_memory.c needs it too when it fallbacks in copying hugepages into regular
> fragmented pages if hugepage allocation fails during COW.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> Acked-by: Rik van Riel <riel@...hat.com>
> Acked-by: Mel Gorman <mel@....ul.ie>

It wasn't good idea to do it. mm/memory.c is used only for system with 
MMU. System without MMU are broken.

Not sure what the right fix is but anyway I think use one ifdef make 
sense (git patch in attachment).

Regards,
Michal


diff --git a/include/linux/mm.h b/include/linux/mm.h
index 956a355..f6385fc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -470,6 +470,7 @@ static inline void set_compound_order(struct page 
*page, unsigned long order)
  	page[1].lru.prev = (void *)order;
  }

+#ifdef CONFIG_MMU
  /*
   * Do pte_mkwrite, but only if the vma says VM_WRITE.  We do this when
   * servicing faults for write access.  In the normal case, do always want
@@ -482,6 +483,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct 
vm_area_struct *vma)
  		pte = pte_mkwrite(pte);
  	return pte;
  }
+#endif

  /*
   * Multiple processes may "see" the same page. E.g. for untouched


> ---
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -416,6 +416,19 @@ static inline void set_compound_order(st
>  }
>  
>  /*
> + * Do pte_mkwrite, but only if the vma says VM_WRITE.  We do this when
> + * servicing faults for write access.  In the normal case, do always want
> + * pte_mkwrite.  But get_user_pages can cause write faults for mappings
> + * that do not have writing enabled, when used by access_process_vm.
> + */
> +static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> +{
> +	if (likely(vma->vm_flags & VM_WRITE))
> +		pte = pte_mkwrite(pte);
> +	return pte;
> +}
> +
> +/*
>   * Multiple processes may "see" the same page. E.g. for untouched
>   * mappings of /dev/null, all processes see the same page full of
>   * zeroes, and text pages of executables and shared libraries have
> diff --git a/mm/memory.c b/mm/memory.c
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2048,19 +2048,6 @@ static inline int pte_unmap_same(struct 
>  	return same;
>  }
>  
> -/*
> - * Do pte_mkwrite, but only if the vma says VM_WRITE.  We do this when
> - * servicing faults for write access.  In the normal case, do always want
> - * pte_mkwrite.  But get_user_pages can cause write faults for mappings
> - * that do not have writing enabled, when used by access_process_vm.
> - */
> -static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma)
> -{
> -	if (likely(vma->vm_flags & VM_WRITE))
> -		pte = pte_mkwrite(pte);
> -	return pte;
> -}
> -
>  static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
>  {
>  	/*
> --
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-- 
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663

View attachment "0001-mm-System-without-MMU-do-not-need-pte_mkwrite.patch" of type "text/x-patch" (1133 bytes)