linux-kernel - Re: [discuss] [Patch] 4/5 in support of hot-add memory x86

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Date:	Sat, 29 Jul 2006 13:11:13 -0700
From:	keith mannthey <kmannth@...ibm.com>
To:	Andi Kleen <ak@...e.de>
Cc:	discuss <discuss@...-64.org>, lkml <linux-kernel@...r.kernel.org>,
	lhms-devel <lhms-devel@...ts.sourceforge.net>,
	andrew <akpm@...l.org>, kame <kamezawa.hiroyu@...fujitsu.com>,
	dave hansen <haveblue@...ibm.com>, konrad <darnok@...ibm.com>
Subject: Re: [discuss] [Patch] 4/5 in support of hot-add memory x86_64 fix
	kernel mapping code

On Sat, 2006-07-29 at 18:32 +0200, Andi Kleen wrote:
> On Saturday 29 July 2006 04:52, keith mannthey wrote:
> > Hello All,
> >
> >   phys_pud_init is broken when using it at runtime with some offsets.
> > It currently only maps one pud entry worth of pages while trampling any
> > mappings that may have existed on the pmd_page :(
> 
> To print x86-64 ptes you need a %016lx (or just %lx) 

Thanks. 
> it would be cleaner to recompute pmd inside the loop based on i
> and use a standard for() 

sure I can do away with the pmd++ pud++ in the for loops. 
> 
> It is unclear why you hardcode 0 as address in phys_pmd_update
> when a real address is passed in

When the pud is already set there a 2 options.  

1. You need to initialize pmds at the start of the pmd_page. 
2. You need to initialize pmds starting at some offset of the pmd_page.

When calling phys_pmd_init you need to pass it the start of the pmd_page
not some random pmd with in the page.  
pmd = alloc_low_page(&map, &pmd_phys); 
always gives us the start of the pmd_page.  I keep this idea for the
update path as well. 
pmd_offset(pud,0) does just this. Maybe there is a better macro to use?

Things could be different is terms of flexibility of what you pass in
(more changes are involved) but this set of changes seemed to be min-
tampering of the current code. 

Also in general is there some reason kernel mapping code is arch
specific?  This all seems to be pretty generic.

Thanks,
  Keith 

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