xen-balloon: Add interface to retrieve ballooned pages
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.
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
[v2: Deal with rebasing on top of modified balloon code]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index 7497041..8c81cd2 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -128,14 +128,17 @@
}
/* 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)) {
@@ -233,7 +236,7 @@
return BP_EAGAIN;
for (i = 0; i < rc; i++) {
- page = balloon_retrieve();
+ page = balloon_retrieve(false);
BUG_ON(page == NULL);
pfn = page_to_pfn(page);
@@ -263,7 +266,7 @@
return BP_DONE;
}
-static enum bp_state decrease_reservation(unsigned long nr_pages)
+static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp)
{
enum bp_state state = BP_DONE;
unsigned long pfn, i;
@@ -279,7 +282,7 @@
nr_pages = ARRAY_SIZE(frame_list);
for (i = 0; i < nr_pages; i++) {
- if ((page = alloc_page(GFP_BALLOON)) == NULL) {
+ if ((page = alloc_page(gfp)) == NULL) {
nr_pages = i;
state = BP_EAGAIN;
break;
@@ -340,7 +343,7 @@
state = increase_reservation(credit);
if (credit < 0)
- state = decrease_reservation(-credit);
+ state = decrease_reservation(-credit, GFP_BALLOON);
state = update_schedule(state);
@@ -366,6 +369,64 @@
}
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(true);
+ if (page) {
+ pages[pgno++] = page;
+ } else {
+ enum bp_state st;
+ st = decrease_reservation(nr_pages - pgno, GFP_HIGHUSER);
+ if (st != BP_DONE)
+ 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_delayed_work(&balloon_worker, 0);
+ 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_delayed_work(&balloon_worker, 0);
+
+ mutex_unlock(&balloon_mutex);
+}
+EXPORT_SYMBOL(free_xenballooned_pages);
+
static int __init balloon_init(void)
{
unsigned long pfn, extra_pfn_end;
diff --git a/include/xen/balloon.h b/include/xen/balloon.h
index f72e479..a2b22f0 100644
--- a/include/xen/balloon.h
+++ b/include/xen/balloon.h
@@ -20,3 +20,6 @@
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);