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SubjectRe: [PATCH v10 Golden] Unified trace buffer
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On Tue, 2008-09-30 at 12:48 -0400, Steven Rostedt wrote:
> On Tue, 30 Sep 2008, Linus Torvalds wrote:
> >
> > Trace buffers are different, though. Do people realize that doing the
> > overloading means that you never EVER can use those buffers for anything
> > else? Do people realize that it means that splice() and friends are out of
> > the question?
> >
> > > Trouble is, looking at it I see no easy way out,
> >
> > Quite frankly, we could just put it at the head of the page itself. Having
> > a "whole page" for the trace data is not possible anyway, since the trace
> > header itself will always eat 8 bytes.
> >
> > And I do think it would potentially be a better model. Or at least safer.
>
> Actually, looking at the code, there is no reason I need to keep this in
> the frame buffer itself. I've also encapsulated the accesses to the
> incrementing of the pointers so it would be trivial to try other
> approaches.
>
> The problem we had with the big array struct is that we can want large
> buffers and to do that with pointers means we would need to either come up
> with a large allocator or use vmap.
>
> But I just realized that I could also just make a link list of page
> pointers and do the exact same thing without having to worry about page
> frames. Again, the way I coded this up, it is quite trivial to replace
> the handling of the pages with other schemes.

The list_head in the page frame should be available regardless of
splice() stuffs.



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