Jakub Jelinek wrote:

> My guess is that all the page zeroing is pretty expensive as well and
> takes significant time, but I haven't profiled it.

With the attached patch (Andrew, I'll change the details around
if you want - I just wanted something to test now), your test
case run time went down considerably.

I modified the test case to only run 1000 loops, so it would run
a bit faster on my system.  I also modified it to use MADV_DONTNEED
to zap the pages, instead of the mmap(PROT_NONE) thing you use.


MADV_DONTNEED, unpatched, 1000 loops

real    0m13.672s
user    0m1.217s
sys     0m45.712s


MADV_DONTNEED, with patch, 1000 loops

real    0m4.169s
user    0m2.033s
sys     0m3.224s


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