Re: [patch 00/14] remap_file_pages protection support

From: Nick Piggin
Date: Tue May 16 2006 - 23:24:38 EST

Andreas Mohr wrote:


On Tue, May 16, 2006 at 09:31:12AM -0700, Valerie Henson wrote:

On Tue, May 16, 2006 at 03:51:35PM +0200, Andreas Mohr wrote:

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.

This is important: Which kernel?

I had some traces still showing find_vma prominently during a profiling run
just yesterday, with a very fresh 2.6.17-rc4-ck1 (IOW, basically 2.6.17-rc4).
I added some cache prefetching in the list traversal a while ago, and IIRC
that improved profiling times there, but cache prefetching is very often
a bandaid in search for a real solution: a better data-handling algorithm.

If you want to try out the patch and see what it does for you, that would be
interesting. I'll repost a slightly cleaned up version in a couple of hours.


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