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Date: Sun, 09 Sep 2012 23:42:10 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
alan@...rguk.ukuu.org.uk, Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>,
Russell King <rmk+kernel@....linux.org.uk>
Subject: [ 20/95] ARM: 7488/1: mm: use 5 bits for swapfile type encoding
3.2-stable review patch. If anyone has any objections, please let me know.
------------------
From: Will Deacon <will.deacon@....com>
commit f5f2025ef3e2cdb593707cbf87378761f17befbe upstream.
Page migration encodes the pfn in the offset field of a swp_entry_t.
For LPAE, we support physical addresses of up to 36 bits (due to
sparsemem limitations with the size of page flags), requiring 24 bits
to represent a pfn. A further 3 bits are used to encode a swp_entry into
a pte, leaving 5 bits for the type field. Furthermore, the core code
defines MAX_SWAPFILES_SHIFT as 5, so the additional type bit does not
get used.
This patch reduces the width of the type field to 5 bits, allowing us
to create up to 31 swapfiles of 64GB each.
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
arch/arm/include/asm/pgtable.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index d88f9f0..41dc31f 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -253,13 +253,13 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
*
* 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
* 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
- * <--------------- offset --------------------> <- type --> 0 0 0
+ * <--------------- offset ----------------------> < type -> 0 0 0
*
- * This gives us up to 63 swap files and 32GB per swap file. Note that
+ * This gives us up to 31 swap files and 64GB per swap file. Note that
* the offset field is always non-zero.
*/
#define __SWP_TYPE_SHIFT 3
-#define __SWP_TYPE_BITS 6
+#define __SWP_TYPE_BITS 5
#define __SWP_TYPE_MASK ((1 << __SWP_TYPE_BITS) - 1)
#define __SWP_OFFSET_SHIFT (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT)
--
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