Re: [PATCH V4] mm: Add sysfs interface to dump each node's zonelist information

From: David Rientjes
Date: Mon Sep 19 2016 - 20:54:37 EST

On Sat, 17 Sep 2016, Anshuman Khandual wrote:

> > I'm questioning if this information can be inferred from information
> > already in /proc/zoneinfo and sysfs. We know the no-fallback zonelist is
> > going to include the local node, and we know the other zonelists are
> > either node ordered or zone ordered (or do we need to extend
> > vm.numa_zonelist_order for default?). I may have missed what new
> > knowledge this interface is imparting on us.
> IIUC /proc/zoneinfo lists down zone internal state and statistics for
> all zones on the system at any given point of time. The no-fallback
> list contains the zones from the local node and fallback (which gets
> used more often than the no-fallback) list contains all zones either
> in node-ordered or zone-ordered manner. In most of the platforms the
> default being the node order but the sequence of present nodes in
> that order is determined by various factors like NUMA distance, load,
> presence of CPUs on the node etc. This order of nodes in the fallback
> list is the most important information derived out of this interface.

The point is that all of this can be inferred with information already
provided, so the additional interface seems unnecessary. The only
extension I think that is needed is to determine if the order is node or
zone when vm.numa_zonelist_order == default and we shouldn't parse this
from dmesg.