Messages in this thread | | | Date | Wed, 16 Oct 2002 10:03:52 +0200 (CEST) | From | Ingo Molnar <> | Subject | Re: [patch] mmap-speedup-2.5.42-C3 |
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On 15 Oct 2002, Andi Kleen wrote:
> When you oprofile KDE startup you notice that a lot of time is spent in > get_unmapped_area too. The reason is that every KDE process links with > 10-20 libraries and ends up with a 40-50 entry /proc/<pid>/maps.
actually, library mappings alone should not cause a slowdown, since we start the search at MAP_UNMAPPED_BASE and most library mappings are below 1GB. But if those libraries use mmap()-ed anonymous RAM that has different protections then the anonymous areas do not get merged and the scanning overhead goes up.
> Optimizing this case would be likely useful too, although I suspect > Ingo's last hit cache would already help somewhat.
well, could you check how much of an impact it has on KDE's kernel profile? For the threaded test it's was a more than 10x application speedup, and in the kernel profile get_unmapped_area() was like 90% of the hits - after the change it was like 1% of the hits. (but, this test is the best-case for the search cache, so ...)
if this simpler approach solves two different problem categories sufficiently then i cannot see any reason to go for the much more complex (and still not 100% scanning-less) approach.
Ingo
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