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author | Russell King <rmk@dyn-67.arm.linux.org.uk> | 2009-07-05 11:30:15 +0100 |
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committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2009-07-05 15:31:26 +0100 |
commit | fb93a1c75eb646fde35985e9af23da936775ae52 (patch) | |
tree | 345ad933ae9a1c114c4185b7578e9ddf08c608a2 /arch/arm/include/asm/pgtable.h | |
parent | ba9b42e4ff5eb68f9c946378229d7e45299d7151 (diff) | |
download | linux-fb93a1c75eb646fde35985e9af23da936775ae52.tar.bz2 |
[ARM] pgtable: swp pte layout documentation, definitions, and check
Document the layout of our swp PTE entries, adding definitions for
the bit masks/shifts/sizes, and implement MAX_SWAPFILES_CHECK()
such that we fail to build if we are unable to properly encode the
swp type field.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/include/asm/pgtable.h')
-rw-r--r-- | arch/arm/include/asm/pgtable.h | 30 |
1 files changed, 25 insertions, 5 deletions
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h index 1cd2d6416bda..c1d97938f3e2 100644 --- a/arch/arm/include/asm/pgtable.h +++ b/arch/arm/include/asm/pgtable.h @@ -384,16 +384,36 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot) extern pgd_t swapper_pg_dir[PTRS_PER_PGD]; -/* Encode and decode a swap entry. +/* + * Encode and decode a swap entry. Swap entries are stored in the Linux + * page tables as follows: + * + * 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 * - * We support up to 32GB of swap on 4k machines + * This gives us up to 127 swap files and 32GB per swap file. Note that + * the offset field is always non-zero. */ -#define __swp_type(x) (((x).val >> 2) & 0x7f) -#define __swp_offset(x) ((x).val >> 9) -#define __swp_entry(type,offset) ((swp_entry_t) { ((type) << 2) | ((offset) << 9) }) +#define __SWP_TYPE_SHIFT 2 +#define __SWP_TYPE_BITS 7 +#define __SWP_TYPE_MASK ((1 << __SWP_TYPE_BITS) - 1) +#define __SWP_OFFSET_SHIFT (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT) + +#define __swp_type(x) (((x).val >> __SWP_TYPE_SHIFT) & __SWP_TYPE_MASK) +#define __swp_offset(x) ((x).val >> __SWP_OFFSET_SHIFT) +#define __swp_entry(type,offset) ((swp_entry_t) { ((type) << __SWP_TYPE_SHIFT) | ((offset) << __SWP_OFFSET_SHIFT) }) + #define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) }) #define __swp_entry_to_pte(swp) ((pte_t) { (swp).val }) +/* + * It is an error for the kernel to have more swap files than we can + * encode in the PTEs. This ensures that we know when MAX_SWAPFILES + * is increased beyond what we presently support. + */ +#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > __SWP_TYPE_BITS) + /* Needs to be defined here and not in linux/mm.h, as it is arch dependent */ /* FIXME: this is not correct */ #define kern_addr_valid(addr) (1) |