Re: [patch 00/14] remap_file_pages protection support

From: Andreas Mohr
Date: Tue May 16 2006 - 09:50:59 EST


On Tue, May 16, 2006 at 11:30:32PM +1000, Nick Piggin wrote:
> I also tried running kbuild under UML, and could not make find_vma take
> much time either [in this case, the per-thread vma cache patch roughly
> doubles the number of hits, from about 15%->30% (in the host)].
> So I guess it's time to go back into my hole. If anyone does come across
> a find_vma constrained workload (especially with threads), I'd be very
> interested.

I cannot offer much other than some random confirmation that from my own
oprofiling, whatever I did (often running a load test script consisting of
launching 30 big apps at the same time), find_vma basically always showed up
very prominently in the list of vmlinux-based code (always ranking within the
top 4 or 5 kernel hotspots, such as timer interrupts, ACPI idle I/O etc.pp.).
call-tracing showed it originating from mmap syscalls etc., and AFAIR quite
some find_vma activity from oprofile itself.
Profiling done on 512MB UP Athlon and P3/700, 2.6.16ish, current Debian.
Sorry for the foggy report, I don't have those logs here right now.

So yes, improving that part should help in general, but I cannot quite
say that my machines are "constrained" by it.

But you probably knew that already, otherwise you wouldn't have poked
in there... ;)

Andreas Mohr
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