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

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

Peter Zijlstra wrote:

> 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.

I agree, the VM looks at the usage of individual pages and makes
decisions based on that.  We can only see how often individual
pages are referenced, and do not have much additional information
(except from the readahead code).

Making sweeping generalizations like "unmapping makes pages less
likely to be needed again" is bound to cause trouble for some
workloads.

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