Re: bug #5493

[Rik van Riel <riel@redhat.com>]

On Thu, 8 Nov 2007 10:56:59 -0800
Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Thu, 8 Nov 2007 13:15:18 -0500 Rik van Riel <riel@redhat.com> wrote:
> > On Thu, 8 Nov 2007 09:57:04 -0800

> > > No, it was due to linear traversal of very long reverse-mapping lists
> > > (thousands of elements, irrc).
> > 
> > Traversal at pageout time, or at mprotect time?
> > 
> 
> pageout, iirc.  For each page we were walking a linear list of I think
> ~10,000 elements.

Pageout scan complexity in this workload is O(P*M), where
P is the number of pages scanned and M is the number of
mappings.

My code will, in the next iteration, reduce P by a fair
amount for larger amounts of memory, but M is still very
large...

I might use this test case to play with the SEQ replacement
of anonymous pages.  Figuring out how to avoid some worst
case that people really hit in practice is often educational.

-- 
"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it." - Brian W. Kernighan

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