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Subject[PATCH] mips,mm: Reinstate move_pte optimization
Date
CC to mips folks.

> If something like this or your replacment does go forward,
> then I think that test is better inside the "if (!page->mapping)"
> below. Admittedly that adds even more mm-dependence here (relying
> on a zero page to have NULL page->mapping); but isn't page_to_pfn()
> one of those functions which is trivial on many configs but expensive
> on some? Better call it only in the rare case that it's needed.
>
> Though wouldn't it be even better not to use is_zero_pfn() at all?
> That was convenient in mm/memory.c because it had the pfn or pte right
> at hand, but here a traditional (page == ZERO_PAGE(address)) would be
> more efficient.
>
> Which would save having to move is_zero_pfn() from mm/memory.c
> to include/linux/mm.h - I'd prefer to keep it private if we can.
> But for completeness, this would involve resurrecting the 2.6.19
> MIPS move_pte(), which makes sure mremap() move doesn't interfere
> with our assumptions. Something like
>
> #define __HAVE_ARCH_MOVE_PTE
> pte_t move_pte(pte_t pte, pgprot_t prot, unsigned long old_addr,
> unsigned long new_addr)
> {
> if (pte_present(pte) && is_zero_pfn(pte_pfn(pte)))
> pte = mk_pte(ZERO_PAGE(new_addr), prot);
> return pte;
> }
>
> in arch/mips/include/asm/pgtable.h.

I agree with resurrecting mips move_pte. At least your patch
passed my cross compile test :)

Ralf, can you please review following patch?


======================================================
Subject: [PATCH] mips,mm: Reinstate move_pte optimization
From: Hugh Dickins <hugh.dickins@tiscali.co.uk>
About three years ago, we removed mips specific move_pte by commit
701dfbc1cb (mm: mremap correct rmap accounting). because it is only
small optimization and it has bug.

However new zero-page thing doesn't have such problem and behavior
consistency of mremap have worth a bit.

This patch reinstate it.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: Nick Piggin <npiggin@suse.de>
Cc: Carsten Otte <cotte@de.ibm.com>
---
arch/mips/include/asm/pgtable.h | 8 ++++++++
1 files changed, 8 insertions(+), 0 deletions(-)
diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 1854336..6ad2f73 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -387,6 +387,14 @@ static inline int io_remap_pfn_range(struct vm_area_struct *vma,
remap_pfn_range(vma, vaddr, pfn, size, prot)
#endif

+#define __HAVE_ARCH_MOVE_PTE
+pte_t move_pte(pte_t pte, pgprot_t prot, unsigned long old_addr, unsigned long new_addr)
+{
+ if (pte_present(pte) && is_zero_pfn(pte_pfn(pte)))
+ pte = mk_pte(ZERO_PAGE(new_addr), prot);
+ return pte;
+}
+
#include <asm-generic/pgtable.h>

/*
--
1.6.5.2




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