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

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Message-Id: <57FF9C4B.5040004@linux.vnet.ibm.com>
Date:   Thu, 13 Oct 2016 20:08:03 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     David Rientjes <rientjes@...gle.com>,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
CC:     Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH V4] mm: Add sysfs interface to dump each node's zonelist
 information

On 09/20/2016 06:24 AM, David Rientjes wrote:
> 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.

Okay. Seems like the general view is that this interface is not necessary.
Hence wont be posting the debugfs version for now.