On 03/07/2016 12:16 PM, David Miller wrote:
From: Khalid Aziz <redacted>
Date: Mon, 7 Mar 2016 11:24:54 -0700
quoted
Tags can be cleared by user by setting tag to 0. Tags are
automatically cleared by the hardware when the mapping for a virtual
address is removed from TSB (which is why swappable pages are a
problem), so kernel does not have to do it as part of clean up.
You might be able to crib some bits for the Tag in the swp_entry_t, it's
64-bit and you can therefore steal bits from the offset field.
That way you'll have the ADI tag in the page tables, ready to re-install
at swapin time.
That is a possibility but limited in scope. An address range covered by a single TTE can have large number of tags. Version tags are set on cacheline. In extreme case, one could set a tag for each set of 64-bytes in a page. Also tags are set completely in userspace and no transition occurs to kernel space, so kernel has no idea of what tags have been set. I have not found a way to query the MMU on tags.
I will think some more about it.
Thanks,
Khalid
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