linux-kernel - Re: NUMA node information for pages

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Message-ID: <alpine.DEB.2.02.1404101500280.11995@chino.kir.corp.google.com>
Date:	Thu, 10 Apr 2014 15:06:49 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
cc:	drepper@...il.com, anatol.pomozov@...il.com, jkosina@...e.cz,
	akpm@...ux-foundation.org, xemul@...allels.com,
	paul.gortmaker@...driver.com, linux-kernel@...r.kernel.org
Subject: Re: NUMA node information for pages

On Wed, 9 Apr 2014, Naoya Horiguchi wrote:

> >  [ And that block_size_bytes file is absolutely horrid, why are we
> >    exporting all this information in hex and not telling anybody? ]
> 
> Indeed, this kind of implicit hex numbers are commonly used in many place.
> I guess that it's maybe for historical reasons.
> 

I think it was meant to be simple to that you could easily add the length 
to the start, but it should at least prefix this with `0x'.  That code has 
been around for years, though, so we probably can't fix it now.

> > I'd much prefer a single change that works for everybody and userspace can 
> > rely on exporting accurate information as long as sysfs is mounted, and 
> > not even need to rely on getpagesize() to convert from pfn to physical 
> > address: just simple {start,end}_phys_addr files added to 
> > /sys/devices/system/node/nodeN/ for node N.  Online information can 
> > already be parsed for these ranges from /sys/devices/system/node/online.
> 
> OK, so what if some node has multiple address ranges?  I don't think that
> start(end)_phys_addr simply returns minimum (maximum) possible address is optimal,
> because users can't know about void range between valid address ranges
> (non-exist pfn should not belong to any node).
> Are printing multilined (or comma-separated) ranges preferable for example
> like below?
> 
>   $ cat /sys/devices/system/node/nodeN/phys_addr
>   0x0-0x80000000
>   0x100000000-0x180000000
> 

What the...?  nodeN should represent the pgdat for that node and a pgdat 
can only have a single range.  I'm suggesting that 
/sys/devices/system/node/nodeN/start_phys_addr returns 
node_start_pfn(N) << PAGE_SHIFT and 
/sys/devices/system/node/nodeN/end_phys_addr returns
node_end_pfn(N) << PAGE_SHIFT and prefix them correctly this time with 
`0x'.
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