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Commit f5f2025e authored by Will Deacon's avatar Will Deacon Committed by Russell King
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ARM: 7488/1: mm: use 5 bits for swapfile type encoding 



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.

Cc: <stable@vger.kernel.org>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent 47f12043

arch/arm/include/asm/pgtable.h

+3 −3
Original line number Diff line number Diff line
@@ -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)