Re: [benchmark] 1% performance overhead of paravirt_ops on nativekernels

[Linus Torvalds]

On Tue, 9 Jun 2009, Nick Piggin wrote:
> 
> The idea seems nice but isn't the problem that kmap gives back a
> basically 1st class kernel virtual memory? (ie. it can then be used
> by any other CPU at any point without it having to use kmap?).

No, everybody has to use kmap()/kunmap().

The "problem" is that you could in theory run out of kmap frames, since if 
everybody does a kmap() in an interruptible context and you have lots and 
lots of threads doing different pages, you'd run out. But that has nothing 
to do with kmap_atomic(), which is basically limited to just the number of 
CPU's and a (very small) level of nesting.

			Linus
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