On Thu, 24 Mar 2005, Nick Piggin wrote:
>
> OK, attached is my first cut at slimming down the boundary tests.
> I have only had a chance to try it on i386, so I hate to drop it
> on you like this - but I *have* put a bit of thought into it....
> Treat it as an RFC, and I'll try to test it on a wider range of
> things in the next couple of days.
I've stared and stared at it. I think I mostly like it.
It's nicer to be rounding end up than ceiling down.
It's clearly superior to what David and I had, in branching
less (other than in your BUG_ONs), and I do believe your
"if (end - ceiling - 1 < P*_SIZE - 1)" is correct and efficient.
But I still find it harder to understand than ours; and don't
understand at all your comment "end can't have approached ceiling
from above...." - but I think you're bravely trying to explain the case
I sidestepped with a lordly unexplained "end can't go down to 0 there".
Let others decide.
One thing I believe is outright wrong, at least with out-of-tree
patches: your change from "if (addr > end - 1)" to "if (addr >= end)",
after you've just rounded up end (perhaps to 0).
(And let me astonish you by asking for the blank lines back before
pmd_offset and pud_offset!)
Hugh
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