Re: [PATCH 1/5] Use MADV_DONTNEED for freeing in garbage collector

[Andi Kleen <andi at firstfloor dot org>]

> Shouldn't we prefer still "mapped" pages when allocating?  Thus, keep
> the freepages list "sorted"?

Possibly. I can look at it in a followup if you want. 
I would prefer to not complicate this patch too much.

> 
> With the new params to call release_pages less, how does this
> interact with using MADV_DONTNEED?  The only reason to delay
> MADV_DONTNEED is to avoid splitting huge-pages?  Which would
> mean that we should rather be better at controlling where we allocate
> from from the free-list?

I first had a patch that tried to cluster inside the freelist
with multiple passes (and only free aligned quire clusters first), but it 
ran into various problems, so I chose this simpler approach.

With MADV_DONTNEED the param is not really needed I think,
I mainly added the param for the benefit of hosts that don't 
have MADV_DONTNEED to let them not suffer from fragmentation too much.
It would be possible to set the thresholds all to 0 if MADV_DONTNEED
is available.

-Andi