RE: [PATCH] powerpc: Fix assmption of end_of_DRAM() returns end address

RE: [PATCH] powerpc: Fix assmption of end_of_DRAM() returns end address

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: David Miller [mailto:davem@davemloft.net]
> Sent: Wednesday, June 06, 2012 3:51 AM
> To: benh@kernel.crashing.org
> Cc: Bhushan Bharat-R65777; linuxppc-dev@lists.ozlabs.org; linux-
> kernel@vger.kernel.org; galak@kernel.crashing.org; Bhushan Bharat-R65777
> Subject: Re: [PATCH] powerpc: Fix assmption of end_of_DRAM() returns end address
> 
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Date: Wed, 06 Jun 2012 08:17:39 +1000
> 
> > On Tue, 2012-06-05 at 19:25 +0530, Bharat Bhushan wrote:
> >> memblock_end_of_DRAM() returns end_address + 1, not end address.
> >> While some code assumes that it returns end address.
> >
> > Shouldn't we instead fix it the other way around ? IE, make
> > memblock_end_of_DRAM() does what the name implies, which is to return
> > the last byte of DRAM, and fix the -other- callers not to make bad
> > assumptions ?
> 
> That was my impression too when I saw this patch.

Initially I also intended to do so. I initiated a email on linux-mm@  subject "memblock_end_of_DRAM()  return end address + 1" and the only response I received from Andrea was:

"
It's normal that "end" means "first byte offset out of the range". End = not ok.
end = start+size.
This is true for vm_end too. So it's better to keep it that way.
My suggestion is to just fix point 1 below and audit the rest :)
"

Thanks
-Bharat

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RE: [PATCH] powerpc: Fix assmption of end_of_DRAM() returns end address

[Benjamin Herrenschmidt]

On Wed, 2012-06-06 at 00:46 +0000, Bhushan Bharat-R65777 wrote:

> > >> memblock_end_of_DRAM() returns end_address + 1, not end address.
> > >> While some code assumes that it returns end address.
> > >
> > > Shouldn't we instead fix it the other way around ? IE, make
> > > memblock_end_of_DRAM() does what the name implies, which is to
> return
> > > the last byte of DRAM, and fix the -other- callers not to make bad
> > > assumptions ?
> > 
> > That was my impression too when I saw this patch.
> 
> Initially I also intended to do so. I initiated a email on linux-mm@
> subject "memblock_end_of_DRAM()  return end address + 1" and the only
> response I received from Andrea was:
> 
> "
> It's normal that "end" means "first byte offset out of the range". End
> = not ok.
> end = start+size.
> This is true for vm_end too. So it's better to keep it that way.
> My suggestion is to just fix point 1 below and audit the rest :)
> "

Oh well, I don't care enough to fight this battle in my current state so
unless Dave has more stamina than I have today, I'm ok with the patch.

Cheers,
Ben.


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Re: [PATCH] powerpc: Fix assmption of end_of_DRAM() returns end address

[Andrea Arcangeli]

Hi,

On Wed, Jun 06, 2012 at 03:30:17PM +1000, Benjamin Herrenschmidt wrote:
> On Wed, 2012-06-06 at 00:46 +0000, Bhushan Bharat-R65777 wrote:
> 
> > > >> memblock_end_of_DRAM() returns end_address + 1, not end address.
> > > >> While some code assumes that it returns end address.
> > > >
> > > > Shouldn't we instead fix it the other way around ? IE, make
> > > > memblock_end_of_DRAM() does what the name implies, which is to
> > return
> > > > the last byte of DRAM, and fix the -other- callers not to make bad
> > > > assumptions ?
> > > 
> > > That was my impression too when I saw this patch.
> > 
> > Initially I also intended to do so. I initiated a email on linux-mm@
> > subject "memblock_end_of_DRAM()  return end address + 1" and the only
> > response I received from Andrea was:
> > 
> > "
> > It's normal that "end" means "first byte offset out of the range". End
> > = not ok.
> > end = start+size.
> > This is true for vm_end too. So it's better to keep it that way.
> > My suggestion is to just fix point 1 below and audit the rest :)
> > "
> 
> Oh well, I don't care enough to fight this battle in my current state so

I wish you to get well soon Ben!

> unless Dave has more stamina than I have today, I'm ok with the patch.

Well it doesn't really matter in the end what is decided as long as
something is decided :). I was asked through a forward so I only
expressed my preference...

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Re: [PATCH] powerpc: Fix assmption of end_of_DRAM() returns end address

[David Miller]

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Wed, 06 Jun 2012 15:30:17 +1000

> On Wed, 2012-06-06 at 00:46 +0000, Bhushan Bharat-R65777 wrote:
> 
>> > >> memblock_end_of_DRAM() returns end_address + 1, not end address.
>> > >> While some code assumes that it returns end address.
>> > >
>> > > Shouldn't we instead fix it the other way around ? IE, make
>> > > memblock_end_of_DRAM() does what the name implies, which is to
>> return
>> > > the last byte of DRAM, and fix the -other- callers not to make bad
>> > > assumptions ?
>> > 
>> > That was my impression too when I saw this patch.
>> 
>> Initially I also intended to do so. I initiated a email on linux-mm@
>> subject "memblock_end_of_DRAM()  return end address + 1" and the only
>> response I received from Andrea was:
>> 
>> "
>> It's normal that "end" means "first byte offset out of the range". End
>> = not ok.
>> end = start+size.
>> This is true for vm_end too. So it's better to keep it that way.
>> My suggestion is to just fix point 1 below and audit the rest :)
>> "
> 
> Oh well, I don't care enough to fight this battle in my current state so
> unless Dave has more stamina than I have today, I'm ok with the patch.

I'm definitely without the samina to fight something like this right now :)

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