Messages in this thread | | | From | (Linus Torvalds) | Subject | Re: object-based rmap and pte-highmem | Date | Sun, 23 Feb 2003 19:20:36 +0000 (UTC) |
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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.
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