alpha: expose number of page table levels on Kconfig level

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>.

This patch (of 19):

We would want to use number of page table level to define mm_struct.
Let's expose it as CONFIG_PGTABLE_LEVELS.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Acked-by: Richard Henderson <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Matt Turner <[email protected]>
Tested-by: Guenter Roeck <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: David Howells <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Koichi Yasutake <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Russell King <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Tony Luck <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index b7ff9a318c31..bf9e9d3b3792 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -76,6 +76,10 @@ config GENERIC_ISA_DMA
 	bool
 	default y
 
+config PGTABLE_LEVELS
+	int
+	default 3
+
 source "init/Kconfig"
 source "kernel/Kconfig.freezer"