Linux: 2.6.34-rc4, “Hunting A Really Annoying VM Regression”

“”It’s been two weeks rather than the usual one, because we’ve
been hunting a really annoying VM regression that not a lot of
people seem to have seen, but I didn’t want to release an -rc4 with
it,” began Linux creator Linus Torvalds, announcing the 2.6.34-rc4
Linux kernel. He explained, “we had the choice of either reverting
all the anon-vma scalability improvements, or finding out exactly
what caused the regression and fixing it. And we got pretty close
to the point where I was going to just revert it all.” Linus
continued:

“”Absolutely _huge_ kudos to Borislav Petkov who reported the
problem and was able to not just reliably reproduce it, but also
test new patches to try to narrow things down at a moments notice.
The thing took ten days of emails flying back and forth, and
Borislav was there all the time, day and night, through several
patches that tried to fix it (several real bugs, but not the one he
hit) and lots of patches to just add instrumentation to get us
nearer to the cause of the problem. And finally, today,
confirmation that we actually nailed the problem. So if anybody has
been seeing a oops (or sometimes a GP fault) in page_referenced(),
that should be gone now.”

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