Re: object-based rmap and pte-highmem

Linus Torvalds
2003-02-23T19:15:17Z

In article <11090000.1046016895@[10.10.2.4]>,
Martin J. Bligh <mbligh@aracnet.com> wrote:
>> So whole stole the remaining 1.85 seconds? Looks like pte_highmem.
>
>I have a plan for that (UKVA) ... we reserve a per-process area with
>kernel type protections (either at the top of user space, changing
>permissions appropriately, or inside kernel space, changing per-process
>vs global appropriately).

Nobody ever seems to have solved the threading impact of UKVA's. I told
Andrea about it almost a year ago, and his reaction was "oh, duh!" and
couldn't come up with a solution either.

The thing is, you _cannot_ have a per-thread area, since all threads
share the same TLB. And if it isn't per-thread, you still need all the
locking and all the scalability stuff that the _current_ pte_highmem
code needs, since there are people with thousands of threads in the same
process.

Until somebody _addresses_ this issue with UKVA, I consider UKVA to be a
pipe-dream of people who haven't thought it through.

Linus