[patch 006/198] arm: add comment about max_low_pfn/max_pfn

[patch 006/198] arm: add comment about max_low_pfn/max_pfn

[akpm]

From: Russell King <rmk+lkml@arm.linux.org.uk>

Oddly, max_low_pfn/max_pfn end up being the number of pages in the system,
rather than the maximum PFN on ARM.  This doesn't seem to cause any problems,
so just add a note about it.

Signed-off-by: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 25-akpm/arch/arm/mm/init.c |    3 +++
 1 files changed, 3 insertions(+)

diff -puN arch/arm/mm/init.c~arm-add-comment-about-max_low_pfn-max_pfn arch/arm/mm/init.c
--- 25/arch/arm/mm/init.c~arm-add-comment-about-max_low_pfn-max_pfn	2005-04-12 03:21:04.967381744 -0700
+++ 25-akpm/arch/arm/mm/init.c	2005-04-12 03:21:04.971381136 -0700
@@ -223,6 +223,9 @@ find_memend_and_nodes(struct meminfo *mi
 	 * This doesn't seem to be used by the Linux memory
 	 * manager any more.  If we can get rid of it, we
 	 * also get rid of some of the stuff above as well.
+	 *
+	 * Note: max_low_pfn and max_pfn reflect the number
+	 * of _pages_ in the system, not the maximum PFN.
 	 */
 	max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
 	max_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
_

Re: [patch 006/198] arm: add comment about max_low_pfn/max_pfn

[Coywolf Qi Hunt]

I told rmk about this long time ago.

On 4/12/05, akpm@osdl.org <akpm@osdl.org> wrote:
> 
> From: Russell King <rmk+lkml@arm.linux.org.uk>
> 
> Oddly, max_low_pfn/max_pfn end up being the number of pages in the system,
> rather than the maximum PFN on ARM.  This doesn't seem to cause any problems,
> so just add a note about it.
> 
> Signed-off-by: Russell King <rmk@arm.linux.org.uk>
> Signed-off-by: Andrew Morton <akpm@osdl.org>
> ---
> 
>  25-akpm/arch/arm/mm/init.c |    3 +++
>  1 files changed, 3 insertions(+)
> 
> diff -puN arch/arm/mm/init.c~arm-add-comment-about-max_low_pfn-max_pfn arch/arm/mm/init.c
> --- 25/arch/arm/mm/init.c~arm-add-comment-about-max_low_pfn-max_pfn     2005-04-12 03:21:04.967381744 -0700
> +++ 25-akpm/arch/arm/mm/init.c  2005-04-12 03:21:04.971381136 -0700
> @@ -223,6 +223,9 @@ find_memend_and_nodes(struct meminfo *mi
>          * This doesn't seem to be used by the Linux memory
>          * manager any more.  If we can get rid of it, we
>          * also get rid of some of the stuff above as well.
> +        *
> +        * Note: max_low_pfn and max_pfn reflect the number
> +        * of _pages_ in the system, not the maximum PFN.
>          */
>         max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
>         max_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
> _


-- 
Coywolf Qi Hunt
http://sosdg.org/~coywolf/

Re: [patch 006/198] arm: add comment about max_low_pfn/max_pfn

[Coywolf Qi Hunt]

FYI
http://lkml.org/lkml/2004/6/29/57

On 4/13/05, Coywolf Qi Hunt <coywolf@gmail.com> wrote:
> I told rmk about this long time ago.
> 
> On 4/12/05, akpm@osdl.org <akpm@osdl.org> wrote:
> >
> > From: Russell King <rmk+lkml@arm.linux.org.uk>
> >
> > Oddly, max_low_pfn/max_pfn end up being the number of pages in the system,
> > rather than the maximum PFN on ARM.  This doesn't seem to cause any problems,
> > so just add a note about it.
> >
> > Signed-off-by: Russell King <rmk@arm.linux.org.uk>
> > Signed-off-by: Andrew Morton <akpm@osdl.org>
> > ---
> >
> >  25-akpm/arch/arm/mm/init.c |    3 +++
> >  1 files changed, 3 insertions(+)
> >
> > diff -puN arch/arm/mm/init.c~arm-add-comment-about-max_low_pfn-max_pfn arch/arm/mm/init.c
> > --- 25/arch/arm/mm/init.c~arm-add-comment-about-max_low_pfn-max_pfn     2005-04-12 03:21:04.967381744 -0700
> > +++ 25-akpm/arch/arm/mm/init.c  2005-04-12 03:21:04.971381136 -0700
> > @@ -223,6 +223,9 @@ find_memend_and_nodes(struct meminfo *mi
> >          * This doesn't seem to be used by the Linux memory
> >          * manager any more.  If we can get rid of it, we
> >          * also get rid of some of the stuff above as well.
> > +        *
> > +        * Note: max_low_pfn and max_pfn reflect the number
> > +        * of _pages_ in the system, not the maximum PFN.
> >          */
> >         max_low_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
> >         max_pfn = memend_pfn - O_PFN_DOWN(PHYS_OFFSET);
> > _
> 
> --
> Coywolf Qi Hunt
> http://sosdg.org/~coywolf/
> 


-- 
Coywolf Qi Hunt
http://sosdg.org/~coywolf/

Re: [patch 006/198] arm: add comment about max_low_pfn/max_pfn

[Russell King]

On Wed, Apr 13, 2005 at 11:10:35AM +0800, Coywolf Qi Hunt wrote:
> I told rmk about this long time ago.

The kernel is a mess of DMA masks and maximum PFNs which all assume
that memory always starts at zero, which I've mentioned before as
well.

I might see about fixing this up properly when it causes real
problems, but until then its better to document the behaviour.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core