tree 7b2ada69ff7e3c1fae20ec0b1dffe5e0d0ec2cc6
parent fbd70035fb2b03deb346052084794bc1d0e25aa2
author Martin Schwidefsky <schwidefsky@de.ibm.com> 1374610302 +0200
committer Martin Schwidefsky <schwidefsky@de.ibm.com> 1377775211 +0200

s390/mm: implement software referenced bits

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>