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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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3
mm/rmap.c
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@ -873,9 +873,6 @@ int page_referenced(struct page *page,
vm_flags);
if (we_locked)
unlock_page(page);
if (page_test_and_clear_young(page_to_pfn(page)))
referenced++;
}
out:
return referenced;