Re: [patch 00/14] remap_file_pages protection support

[Blaisorblade]

On Tuesday 02 May 2006 05:45, Nick Piggin wrote:
> blaisorblade@xxxxxxxx wrote:
> > This will be useful since the VMA lookup at fault time can be a
> > bottleneck for some programs (I've received a report about this from
> > Ulrich Drepper and I've been told that also Val Henson from Intel is
> > interested about this). I guess that since we use RB-trees, the slowness
> > is also due to the poor cache locality of RB-trees (since RB nodes are
> > within VMAs but aren't accessed together with their content), compared
> > for instance with radix trees where the lookup has high cache locality
> > (but they have however space usage problems, possibly bigger, on 64-bit
> > machines).

> Let's try get back to the good old days when people actually reported
> their bugs (togther will *real* numbers) to the mailing lists. That way,
> everybody gets to think about and discuss the problem.

I've not seen the numbers indeed, I've been told of a problem with a "customer 
program" and Ingo connected my work with this problem. Frankly, I've been 
always astonished about how looking up a 10-level tree can be slow. Poor 
cache locality is the only thing that I could think about.

That said, it was an add-on, not the original motivation of the work.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade
Chiacchiera con i tuoi amici in tempo reale! 
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