We encode offset from swapcache page in __swp_entry() this way, see [1]:
| /* Encode swap {type,off} tuple into PTE
| * We reserve 13 bits for 5-bit @type, keeping bits 12-5 zero, ensuring that
| * PAGE_PRESENT is zero in a PTE holding swap "identifier"
| */
| #define __swp_entry(type, off) ((swp_entry_t) { \
| ((type) & 0x1f) | ((off) << 13) })
But decode in __swp_offset() as:
| #define __swp_offset(pte_lookalike) ((pte_lookalike).val << 13)
which is obviously wrong, we should ">> 13" instead.
This basically fixes swap usage on ARC finally.
| # mkswap /dev/sda2
|
| # swapon -a -e /dev/sda2
| Adding 500728k swap on /dev/sda2. Priority:-2 extents:1 across:500728k
|
| # free
| total used free shared buffers cached
| Mem: 765104 13456 751648 4736 8 4736
| -/+ buffers/cache: 8712 756392
| Swap: 500728 0 500728
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arc/include/asm/pgtable.h#n375
Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>
Cc: stable at vger.kernel.org
---
arch/arc/include/asm/pgtable.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arc/include/asm/pgtable.h b/arch/arc/include/asm/pgtable.h
index 08fe33830d4b..77676e18da69 100644
--- a/arch/arc/include/asm/pgtable.h
+++ b/arch/arc/include/asm/pgtable.h
@@ -379,7 +379,7 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
/* Decode a PTE containing swap "identifier "into constituents */
#define __swp_type(pte_lookalike) (((pte_lookalike).val) & 0x1f)
-#define __swp_offset(pte_lookalike) ((pte_lookalike).val << 13)
+#define __swp_offset(pte_lookalike) ((pte_lookalike).val >> 13)
/* NOPs, to keep generic kernel happy */
#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
--
2.17.1
