Xen devel - May 2012 - [PATCH] xen/balloon: Subtract from xen_released_pages the count that is populated.

We did not take into account that xen_released_pages would be
used outside the initial E820 parsing code. As such we would
not subtract from xen_released_pages the count of pages
that we had populated back. Instead we just did a simple
extra_pages = released - populated calculation.

However the balloon worker uses xen_released_pages to figure
out how many more pages it can balloon up to and not having
the proper numbers we would balloon more than we should have.

This fixes errors such as:

(XEN) memory.c:133:d0 Could not allocate order=0 extent: id=0 memflags=0 (51 of
512)
during bootup and
free_memory            : 0

where the free_memory should be 128.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 arch/x86/xen/setup.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 3ebba07..a4790bf 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -371,7 +371,8 @@ char * __init xen_memory_setup(void)
 	populated = xen_populate_chunk(map, memmap.nr_entries,
 			max_pfn, &last_pfn, xen_released_pages);
 
-	extra_pages += (xen_released_pages - populated);
+	xen_released_pages -= populated;
+	extra_pages += xen_released_pages;
 
 	if (last_pfn > max_pfn) {
 		max_pfn = min(MAX_DOMAIN_PAGES, last_pfn);
-- 
1.7.7.6

On 29/05/12 17:58, Konrad Rzeszutek Wilk wrote:
> We did not take into account that xen_released_pages would be
> used outside the initial E820 parsing code. As such we would
> not subtract from xen_released_pages the count of pages
> that we had populated back. Instead we just did a simple
> extra_pages = released - populated calculation.
> 
> However the balloon worker uses xen_released_pages to figure
> out how many more pages it can balloon up to and not having
> the proper numbers we would balloon more than we should have.
I would probably rephrase this paragraph to be a bit clearer but it''s
not a big deal.  Something like this perhaps:

"The balloon driver uses xen_released_pages to set the initial
current_pages count.  If this is wrong (too low) then when a new
(higher) target is set, the balloon driver will request too many pages
from Xen."
> This fixes errors such as:
> 
> (XEN) memory.c:133:d0 Could not allocate order=0 extent: id=0 memflags=0
(51 of 512)
> during bootup and
> free_memory            : 0
> 
> where the free_memory should be 128.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>
> ---
>  arch/x86/xen/setup.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 3ebba07..a4790bf 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -371,7 +371,8 @@ char * __init xen_memory_setup(void)
>  	populated = xen_populate_chunk(map, memmap.nr_entries,
>  			max_pfn, &last_pfn, xen_released_pages);
>  
> -	extra_pages += (xen_released_pages - populated);
> +	xen_released_pages -= populated;
> +	extra_pages += xen_released_pages;
>  
>  	if (last_pfn > max_pfn) {
>  		max_pfn = min(MAX_DOMAIN_PAGES, last_pfn);