| From | Greg Kroah-Hartman <> | Subject | [ 06/85] ARM: 7488/1: mm: use 5 bits for swapfile type encoding | Date | Wed, 12 Sep 2012 16:35:49 -0700 |
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From: Greg KH <gregkh@linuxfoundation.org>
3.4-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon <will.deacon@arm.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@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- arch/arm/include/asm/pgtable.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- 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 * * 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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