Re: [PATCH 13 of 66] export maybe_mkwrite

Michal Simek
2011-01-17T14:14:17Z

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Andrea Arcangeli wrote:
> From: Andrea Arcangeli <aarcange@redhat.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@redhat.com>
> Acked-by: Rik van Riel <riel@redhat.com>
> Acked-by: Mel Gorman <mel@csn.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

[-- Attachment #2: 0001-mm-System-without-MMU-do-not-need-pte_mkwrite.patch --]
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>From 9d09534daec636eafed279352c6b34d3b47c3a09 Mon Sep 17 00:00:00 2001
From: Michal Simek <monstr@monstr.eu>
Date: Mon, 17 Jan 2011 15:09:36 +0100
Subject: [PATCH] mm: System without MMU do not need pte_mkwrite

The patch "thp: export maybe_mkwrite"
(sha1 14fd403f2146f740942d78af4e0ee59396ad8eab)
break systems without MMU.

Signed-off-by: Michal Simek <monstr@monstr.eu>
---
include/linux/mm.h | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

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
--
1.5.5.6