[PATCH 1/2] mm: walk_memory_range: Fix typo in comment

[PATCH 1/2] mm: walk_memory_range: Fix typo in comment

[Toshi Kani]

Fix a typo "end_pft" in the comment of walk_memory_range().

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
---
 mm/memory_hotplug.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b81a367b..ae7bcba 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1613,7 +1613,7 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
 /**
  * walk_memory_range - walks through all mem sections in [start_pfn, end_pfn)
  * @start_pfn: start pfn of the memory range
- * @end_pfn: end pft of the memory range
+ * @end_pfn: end pfn of the memory range
  * @arg: argument passed to func
  * @func: callback for each memory section walked
  *

[PATCH 2/2] mm: remove_memory: Fix end_pfn setting

[Toshi Kani]

remove_memory() calls walk_memory_range() with [start_pfn, end_pfn),
where end_pfn is exclusive in this range.  Therefore, end_pfn needs
to be set to the next page of the end address.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
---
 mm/memory_hotplug.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index ae7bcba..3e2ab7b 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1801,7 +1801,7 @@ int __ref remove_memory(int nid, u64 start, u64 size)
 	int retry = 1;
 
 	start_pfn = PFN_DOWN(start);
-	end_pfn = start_pfn + PFN_DOWN(size);
+	end_pfn = PFN_UP(start + size - 1);
 
 	/*
 	 * When CONFIG_MEMCG is on, one memory block may be used by other

Re: [PATCH 2/2] mm: remove_memory: Fix end_pfn setting

[Andrew Morton]

On Fri,  8 Mar 2013 08:41:41 -0700 Toshi Kani <toshi.kani@hp.com> wrote:

> remove_memory() calls walk_memory_range() with [start_pfn, end_pfn),
> where end_pfn is exclusive in this range.  Therefore, end_pfn needs
> to be set to the next page of the end address.
> 
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1801,7 +1801,7 @@ int __ref remove_memory(int nid, u64 start, u64 size)
>  	int retry = 1;
>  
>  	start_pfn = PFN_DOWN(start);
> -	end_pfn = start_pfn + PFN_DOWN(size);
> +	end_pfn = PFN_UP(start + size - 1);
>  
>  	/*
>  	 * When CONFIG_MEMCG is on, one memory block may be used by other

That looks right, although these rounding/boundary things are always
hard.  I wonder if `start' and `size' are ever not multiples of
PAGE_SIZE..

How did you discover this?  Code inspection, or some runtime
malfunction?  Please always include this info when fixing bugs.

Re: [PATCH 2/2] mm: remove_memory: Fix end_pfn setting

[Toshi Kani]

On Fri, 2013-03-08 at 13:31 -0800, Andrew Morton wrote:
> On Fri,  8 Mar 2013 08:41:41 -0700 Toshi Kani <toshi.kani@hp.com> wrote:
> 
> > remove_memory() calls walk_memory_range() with [start_pfn, end_pfn),
> > where end_pfn is exclusive in this range.  Therefore, end_pfn needs
> > to be set to the next page of the end address.
> > 
> > ...
> >
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1801,7 +1801,7 @@ int __ref remove_memory(int nid, u64 start, u64 size)
> >  	int retry = 1;
> >  
> >  	start_pfn = PFN_DOWN(start);
> > -	end_pfn = start_pfn + PFN_DOWN(size);
> > +	end_pfn = PFN_UP(start + size - 1);
> >  
> >  	/*
> >  	 * When CONFIG_MEMCG is on, one memory block may be used by other
> 
> That looks right, although these rounding/boundary things are always
> hard.  I wonder if `start' and `size' are ever not multiples of
> PAGE_SIZE..
> 
> How did you discover this?  Code inspection, or some runtime
> malfunction?  Please always include this info when fixing bugs.

It was found in code inspection.  For ACPI memory hot-delete, both start
and size values are obtained from ACPI, and should always be
page-aligned.  So, this issue is not exposed at this point.  That said,
it should handle the boundary condition correctly since it might be
called from other path in future.  Yes, I will include such info when
fixing bugs.

Thanks,
-Toshi