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

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

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 |   54 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/xen/balloon.h |    3 ++
 2 files changed, 57 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index b0a7a92..be53596 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -328,6 +328,60 @@ void balloon_set_new_target(unsigned long target)
 }
 EXPORT_SYMBOL_GPL(balloon_set_new_target);
 
+/**
+ * get_ballooned_pages - get pages that have been ballooned out
+ * @nr_pages: Number of pages to get
+ * @pages: pages returned
+ * @force: Try to balloon out more pages if needed
+ * @return number of pages retrieved
+ */
+int get_ballooned_pages(int nr_pages, struct page** pages, int force)
+{
+       int rv = 0;
+       struct page* page;
+       mutex_lock(&balloon_mutex);
+       /* Pages are pulled off the back of the queue to prefer highmem */
+       while (rv < nr_pages) {
+               if (list_empty(&ballooned_pages)) {
+                       if (!force)
+                               break;
+                       if (decrease_reservation(nr_pages - rv))
+                               force = 0;
+               } else {
+                       page = list_entry(ballooned_pages.prev,
+                               struct page, lru);
+                       list_del(&page->lru);
+                       pages[rv++] = page;
+               }
+       }
+       mutex_unlock(&balloon_mutex);
+       return rv;
+}
+EXPORT_SYMBOL(get_ballooned_pages);
+
+/**
+ * put_ballooned_pages - return pages retrieved with get_ballooned_pages
+ * @nr_pages: Number of pages
+ * @pages: pages to return
+ */
+void put_ballooned_pages(int nr_pages, struct page** pages)
+{
+       int i;
+
+       mutex_lock(&balloon_mutex);
+
+       for (i = 0; i < nr_pages; i++) {
+               if (PageHighMem(pages[i])) {
+                       list_add_tail(&pages[i]->lru, &ballooned_pages);
+               } else {
+                       list_add(&pages[i]->lru, &ballooned_pages);
+               }
+       }
+
+       mutex_unlock(&balloon_mutex);
+}
+EXPORT_SYMBOL(put_ballooned_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..5fc25fa 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 get_ballooned_pages(int nr_pages, struct page** pages, int force);
+void put_ballooned_pages(int nr_pages, struct page** pages);
-- 
1.7.3.4


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