linux-kernel - Re: [PATCH] x86/mm/srat_64.c: nodes_parsed should include all nodes detected by ACPI.

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Message-ID: <alpine.DEB.2.00.1001180231430.20677@chino.kir.corp.google.com>
Date:	Mon, 18 Jan 2010 02:43:22 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Haicheng Li <haicheng.li@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm/srat_64.c: nodes_parsed should include all nodes
 detected by ACPI.

On Sun, 17 Jan 2010, Yinghai Lu wrote:

> > There're a couple of issues with this patch:
> >
> > - it breaks CONFIG_MEMORY_HOTPLUG_SPARSE kernels when the SRAT reports
> >  more than one entry for a single node id and the later entry does not
> >  specify an address range, and
> 
> not sure this one.
> 

The old code would preserve the address range from the preceding SRAT 
entry for that node to pass to e820_register_active_regions() when 
CONFIG_MEMORY_HOTPLUG_SPARSE is enabled, this patch incorrectly clears 
that data.

> > - carrying the bit for the node over in nodes_parsed is inappropriate
> >  since other x86 code depends on that map including only nodes with
> >  memory such as e820_register_active_regions() and nodes_cover_memory().
> 
> assume if e820 is right, even srat table have a range for hot plug
> aka the e820 have hole already. then e820_register_active_regions()
> and nodes_cover_memory
> should be ok even bootnode have some pre reserved range.
> 

cpu_nodes_parsed handles nodes without memory, there's no reason why a bit 
should be set in nodes_parsed if its corresponding node does not have a 
valid address range.  We have a reasonable expectation that nodes_parsed 
represents memory nodes given its use for e820_register_active_regions() 
and nodes_cover_memory() as well as acpi_get_nodes() for NUMA emulation, 
for example, which would be broken with this patch.  See dc0985519.
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