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

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Date:   Mon, 12 Sep 2016 11:13:43 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     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 Mon, 12 Sep 2016, Anshuman Khandual wrote:

> >> > after memory or node hot[un]plug is desirable. This change adds one
> >> > new sysfs interface (/sys/devices/system/memory/system_zone_details)
> >> > which will fetch and dump this information.
> > Doesn't this violate the "one value per file" sysfs rule?  Does it
> > belong in debugfs instead?
> 
> Yeah sure. Will make it a debugfs interface.
> 

So the intended reader of this file is running as root?

> > I also really question the need to dump kernel addresses out, filtered 
> > or not.  What's the point?
> 
> Hmm, thought it to be an additional information. But yes its additional
> and can be dropped.
> 

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.