Re: [PATCH for 2.6.16] Handle holes in node mask in node fallback list initialization

[Linus Torvalds <torvalds@osdl.org>]

On Fri, 17 Feb 2006, Andi Kleen wrote:
> 
> That is why I added the !NODE_DATA(...) continue check
> It will just continue until it finds a usable node. 

The thing is, there is nothing to guarantee that it _ever_ finds a usable 
node. Let's say that we have nodes

	3 10

in the node map, then neither the old "i + n % 2" nor your new "i + n % 11" 
will ever actually hit either of the valid nodes at all when you traverse 
the thing. See? 

That's why I'm saying that the "(i + n) % any_random_number" just can't be 
right, and that you absolutely _have_ to use the numbers that 
"for_each_online_node()" gives you directly. Using anything else is always 
going to be buggy.

> > NOTE! I've not tested (and thus not debugged) it. I don't even have NUMA 
> > enabled, so I've not even compiled it. Somebody else please test it, and 
> > send it back to me with a sign-off and a proper explanation, and I'll sign 
> > off on it again and apply it.
> 
> I gave it a quick boot on the simulator with a missing node and it looks 
> good. Will test it a bit more and then resubmit it.

If it compiles (and I didn't just do something stupid like use the wrong 
variable or test the order the wrong way), I think my version is always 
safe. It doesn't play games with the node numbers, and it only really 
edits the "distance function" to have a dependency on the node 
relationship.

So if it works at all, I think it works every time. But I'm biased ;)

And I'll never argue against more testing.

			Linus

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