Re: Avoid allocating during interleave from almost full nodes

[Christoph Lameter <clameter@sgi.com>]

On Fri, 3 Nov 2006, Andrew Morton wrote:

> But in this application which you are proposing, any correlation with
> elapsed walltime is very slight.  It's just the wrong baseline to use. 
> What is the *sense* in it?

You just accepted Paul's use of a similar mechanism to void cached 
zonelists. He has a one second timeout for the cache there it seems.

The sense is that memory on nodes may be freed and then we need to 
allocate from those nodes again.

> Yes.  And it is wrong to do so.  Because a node may well have no "free"
> pages but plenty of completely stale ones which should be reclaimed.

But there may be other nodes that have more free pages. If we allocate 
from those then we can avoid reclaim.

> Reclaim isn't expensive.

It is needlessly expensive if its done for an allocation that is not bound 
to a specific node and there are other nodes with free pages. We may throw 
out pages that we need later.