linux-kernel - Re: [PATCH] x86: numa: drop ZONE

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Message-ID: <alpine.DEB.2.02.1406101506290.32203@chino.kir.corp.google.com>
Date:	Tue, 10 Jun 2014 15:10:01 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Luiz Capitulino <lcapitulino@...hat.com>
cc:	akpm@...ux-foundation.org, andi@...stfloor.org, riel@...hat.com,
	yinghai@...nel.org, isimatu.yasuaki@...fujitsu.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] x86: numa: drop ZONE_ALIGN

On Mon, 9 Jun 2014, Luiz Capitulino wrote:

> > > > > diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h
> > > > > index 4064aca..01b493e 100644
> > > > > --- a/arch/x86/include/asm/numa.h
> > > > > +++ b/arch/x86/include/asm/numa.h
> > > > > @@ -9,7 +9,6 @@
> > > > >  #ifdef CONFIG_NUMA
> > > > >  
> > > > >  #define NR_NODE_MEMBLKS		(MAX_NUMNODES*2)
> > > > > -#define ZONE_ALIGN (1UL << (MAX_ORDER+PAGE_SHIFT))
> > > > >  
> > > > >  /*
> > > > >   * Too small node sizes may confuse the VM badly. Usually they
> > > > > diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c
> > > > > index 1d045f9..69f6362 100644
> > > > > --- a/arch/x86/mm/numa.c
> > > > > +++ b/arch/x86/mm/numa.c
> > > > > @@ -200,8 +200,6 @@ static void __init setup_node_data(int nid, u64 start, u64 end)
> > > > >  	if (end && (end - start) < NODE_MIN_SIZE)
> > > > >  		return;
> > > > >  
> > > > > -	start = roundup(start, ZONE_ALIGN);
> > > > > -
> > > > >  	printk(KERN_INFO "Initmem setup node %d [mem %#010Lx-%#010Lx]\n",
> > > > >  	       nid, start, end - 1);
> > > > >  
> > > > 
> > > > What ensures this start address is page aligned from the BIOS?
> > > 
> > > To which start address do you refer to?
> > 
> > The start address displayed in the dmesg is not page aligned anymore with 
> > your change, correct?  
> 
> I have to check that but I don't expect this to happen because my
> understanding of the code is that what's rounded up here is just discarded
> in free_area_init_node(). Am I wrong?
> 

NODE_DATA(nid)->node_start_pfn needs to be accurate if 
node_set_online(nid).  Since there is no guarantee about page alignment 
from the ACPI spec, removing the roundup() entirely could cause the 
address shift >> PAGE_SIZE to be off by one.  I, like you, do not see the 
need for the ZONE_ALIGN above, but I think we agree that it should be 
replaced with PAGE_SIZE instead.
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