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s390/mm: implement software referenced bits

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The last remaining use for the storage key of the s390 architecture
is reference counting. The alternative is to make page table entries
invalid while they are old. On access the fault handler marks the
pte/pmd as young which makes the pte/pmd valid if the access rights
allow read access. The pte/pmd invalidations required for software
managed reference bits cost a bit of performance, on the other hand
the RRBE/RRBM instructions to read and reset the referenced bits are
quite expensive as well.

Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
2013-07-23 22:11:42 +02:00
parent fbd70035fb
commit 0944fe3f4a
7 changed files with 243 additions and 193 deletions
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4
include/asm-generic/pgtable.h
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@@ -208,10 +208,6 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
#endif
#ifndef __HAVE_ARCH_PAGE_TEST_AND_CLEAR_YOUNG
#define page_test_and_clear_young(pfn) (0)
#endif
#ifndef __HAVE_ARCH_PGD_OFFSET_GATE
#define pgd_offset_gate(mm, addr) pgd_offset(mm, addr)
#endif