Re: [patch] not to disturb page LRU state when unmapping memory range

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Wed, 2007-01-31 at 14:04 -0800, Andrew Morton wrote:

> > Andrew, any strong opinions?
> 
> Not really.  If we change something in there, some workloads will get
> better, some will get worse and most will be unaffected and any regressions
> we cause won't be known until six months later.  The usual deal.
> 
> Remember that all this info is supposed to be estimating what is likely to
> happen to this page in the future - we're not interested in what happened
> in the past, per-se.
> 
> I'd have thought that if multiple processes are touching the same
> page, this is a reason to think that the page will be required again in the
> immediate future.  But you seem to think otherwise?

Yes, why would unmapping a range make the pages more likely to be used
in the immediate future than otherwise indicated by their individual
young bits?

Even the opposite was suggested, that unmapping a range makes it less
likely to be used again.

> > If only I could come up with a proper set of tests that covers all
> > this...
> 
> Well yes, that's rather a sore point.  It's tough.  I wonder what $OTHER_OS
> developers have done.  Probably their tests are priority ordered by
> $market_share of their user's applications :(

Still requires them to set up and run said programs. If we could get a
suite of programs that we consider interesting....

Just hoping, I seem to be stuck with quite a lot of code without means
of evaluation.

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