[Xen-devel] Re: [PATCH 2/3 v4] xen-balloon: Add interface to retrieve ballooned pages

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Tue, 2011-03-08 at 19:49 +0000, Daniel De Graaf wrote:
> Pages that have been ballooned are useful for other Xen drivers doing
> grant table actions, because these pages have valid struct page/PFNs but
> have no valid MFN so are available for remapping.
> 
> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> ---
>  drivers/xen/balloon.c |   65 ++++++++++++++++++++++++++++++++++++++++++++++--
>  include/xen/balloon.h |    3 ++
>  2 files changed, 65 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
> index b0a7a92..d187fce 100644
> --- a/drivers/xen/balloon.c
> +++ b/drivers/xen/balloon.c
> @@ -116,14 +116,17 @@ static void balloon_append(struct page *page)
>  }
>  
>  /* balloon_retrieve: rescue a page from the balloon, if it is not empty. */
> -static struct page *balloon_retrieve(void)
> +static struct page *balloon_retrieve(bool prefer_highmem)
>  {
>       struct page *page;
>  
>       if (list_empty(&ballooned_pages))
>               return NULL;
>  
> -     page = list_entry(ballooned_pages.next, struct page, lru);
> +     if (prefer_highmem)
> +             page = list_entry(ballooned_pages.prev, struct page, lru);
> +     else
> +             page = list_entry(ballooned_pages.next, struct page, lru);
>       list_del(&page->lru);
>  
>       if (PageHighMem(page)) {
> @@ -198,7 +201,7 @@ static int increase_reservation(unsigned long nr_pages)
>               goto out;
>  
>       for (i = 0; i < rc; i++) {
> -             page = balloon_retrieve();
> +             page = balloon_retrieve(0);

You can use "true" and "false" with bools.

Otherwise this and patch 3/3 v4 look good to me.

>               BUG_ON(page == NULL);
>  
>               pfn = page_to_pfn(page);
> @@ -328,6 +331,62 @@ void balloon_set_new_target(unsigned long target)
>  }
>  EXPORT_SYMBOL_GPL(balloon_set_new_target);
>  
> +/**
> + * alloc_xenballooned_pages - get pages that have been ballooned out
> + * @nr_pages: Number of pages to get
> + * @pages: pages returned
> + * @return 0 on success, error otherwise
> + */
> +int alloc_xenballooned_pages(int nr_pages, struct page** pages)
> +{
> +     int pgno = 0;
> +     struct page* page;
> +     mutex_lock(&balloon_mutex);
> +     while (pgno < nr_pages) {
> +             page = balloon_retrieve(1);
> +             if (page) {
> +                     pages[pgno++] = page;
> +             } else {
> +                     if (decrease_reservation(nr_pages - pgno))
> +                             goto out_undo;
> +             }
> +     }
> +     mutex_unlock(&balloon_mutex);
> +     return 0;
> + out_undo:
> +     while (pgno)
> +             balloon_append(pages[--pgno]);
> +     /* Free the memory back to the kernel soon */
> +     schedule_work(&balloon_worker);
> +     mutex_unlock(&balloon_mutex);
> +     return -ENOMEM;
> +}
> +EXPORT_SYMBOL(alloc_xenballooned_pages);
> +
> +/**
> + * free_xenballooned_pages - return pages retrieved with get_ballooned_pages
> + * @nr_pages: Number of pages
> + * @pages: pages to return
> + */
> +void free_xenballooned_pages(int nr_pages, struct page** pages)
> +{
> +     int i;
> +
> +     mutex_lock(&balloon_mutex);
> +
> +     for (i = 0; i < nr_pages; i++) {
> +             if (pages[i])
> +                     balloon_append(pages[i]);
> +     }
> +
> +     /* The balloon may be too large now. Shrink it if needed. */
> +     if (current_target() != balloon_stats.current_pages)
> +             schedule_work(&balloon_worker);
> +
> +     mutex_unlock(&balloon_mutex);
> +}
> +EXPORT_SYMBOL(free_xenballooned_pages);
> +
>  static int __init balloon_init(void)
>  {
>       unsigned long pfn, nr_pages, extra_pfn_end;
> diff --git a/include/xen/balloon.h b/include/xen/balloon.h
> index b2b7c21..72a6927 100644
> --- a/include/xen/balloon.h
> +++ b/include/xen/balloon.h
> @@ -19,3 +19,6 @@ struct balloon_stats {
>  extern struct balloon_stats balloon_stats;
>  
>  void balloon_set_new_target(unsigned long target);
> +
> +int alloc_xenballooned_pages(int nr_pages, struct page** pages);
> +void free_xenballooned_pages(int nr_pages, struct page** pages);



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