Re: [PATCH RFC 08/10] xen/balloon: implement migratepage

[David Vrabel <david.vrabel@citrix.com>]

On 15/10/14 16:54, Wei Liu wrote:
> This patch replaces the xen_balloon_migratepage stub with actual
> implementation.
> 
> It's implemented in two macro steps:
> 1. populate old page with machine page and remove it from balloon driver
> 2. give up machine page that backs new page and queue it to balloon
>    driver
> 
> Old page is the page owned by balloon driver, new page is a page
> isolated by core mm compaction thread.
> 
> The aforementioned steps swaps a ballooned out page with a usable page.
> From guest's point of view, it de-fragments physical address space.
> 
> Signed-off-by: Wei Liu <wei.liu2@citrix.com>
> ---
>  drivers/xen/balloon.c |   94 +++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 92 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index 815e1d5..112190e 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -727,13 +727,103 @@ static struct notifier_block balloon_cpu_notifier = {
>  
>  static const struct address_space_operations xen_balloon_aops;
>  #ifdef CONFIG_BALLOON_COMPACTION
> +/*
> + * xen_balloon_migratepage - perform the balloon page migration on behalf of
> + *                           a compation thread.     (called under page lock)
> + * @mapping: the page->mapping which will be assigned to the new migrated page
> + * @newpage: page that will replace the isolated page after migration finishes
> + * @page   : the isolated (old) page that is about to be migrated to newpage.
> + * @mode   : compaction mode -- not used for balloon page migration.
> + *
> + * After a ballooned page gets isolated by compaction procedures, this
> + * is the function that performs the page migration on behalf of a
> + * compaction thread. The page migration for Xen balloon is done in
> + * these two macro steps:
> + *
> + *  A. back @page with machine page
> + *  B. release machine that backs @newpage

If the target if enforced and the guest is above the target.  This
prevent any compaction.  You need an atomic swap operation.

Also, "frame" is the term for "machine page".

David