> > Once a page is used twice, it's not a candidate for eviction
> > until (most of) the use-once pages are gone.
> >
> > This means that if you have these 40 MB of used-twice-but-never-again
> > buffer cache memory, this memory will never be evicted until other
> > pages get promoted from use-once to active.
>
> Its worth noting btw that you can intentionally exploit this in an app
> to get unfair use of memory. That makes me very dubious about the heuristic
In Rik's VM I had a problem with use-once when Bonnie was doing
rewrite. It's used-twice data became too hard to get rid of at
the aging volume we were doing, leading to an inactive shortage
and unwanted swapping. The active list grew until ~all of ram
was on the active list. I 'fixed' it here by keeping the dirty
list very strictly ordered (lengthened it too) and requiring more
than two accesses before promoting to active.
I have not seen this behavior in the new VM yet.
-Mike
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