linux-kernel - [PATCHv2, RESEND 06/19] m32r: mark PMD folded

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Date:	Fri,  6 Feb 2015 16:50:51 +0200
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv2, RESEND 06/19] m32r: mark PMD folded

Core mm expects __PAGETABLE_{PUD,PMD}_FOLDED to be defined if these page
table levels folded.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Tested-by: Guenter Roeck <linux@...ck-us.net>
---

I've implemented accounting for pmd page tables as we have for pte (see
mm->nr_ptes). It's requires a new counter in mm_struct: mm->nr_pmds.

But the feature doesn't make any sense if an architecture has PMD level
folded and it would be nice get rid of the counter in this case.

The problem is that we cannot use __PAGETABLE_PMD_FOLDED in
<linux/mm_types.h> due to circular dependencies:

<linux/mm_types> -> <asm/pgtable.h> -> <linux/mm_types.h>

In most cases <asm/pgtable.h> wants <linux/mm_types.h> to get definition
of struct page and struct vm_area_struct. I've tried to split mm_struct
into separate header file to be able to user <asm/pgtable.h> there.

But it doesn't fly on some architectures, like ARM: it wants mm_struct
<asm/pgtable.h> to implement tlb flushing. I don't see how to fix it without
massive de-inlining or coverting a lot for inline functions to macros.

This is other approach: expose number of page tables in use via Kconfig
and use it in <linux/mm_types.h> instead of __PAGETABLE_PMD_FOLDED from
<asm/pgtable.h>.

---
 arch/m32r/include/asm/pgtable-2level.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/m32r/include/asm/pgtable-2level.h b/arch/m32r/include/asm/pgtable-2level.h
index 8fd8ee70266a..421e6ba3a173 100644
--- a/arch/m32r/include/asm/pgtable-2level.h
+++ b/arch/m32r/include/asm/pgtable-2level.h
@@ -13,6 +13,7 @@
  * the M32R is two-level, so we don't really have any
  * PMD directory physically.
  */
+#define __PAGETABLE_PMD_FOLDED
 #define PMD_SHIFT	22
 #define PTRS_PER_PMD	1

-- 
2.1.4

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