This patch introduces helper functions that teach compaction and migration bits
how to cope with pages which are part of a guest memory balloon, in order to
make them movable by memory compaction procedures.
Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
---
include/linux/mm.h | 17 +++++++++++++
mm/compaction.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++
mm/migrate.c | 30 +++++++++++++++++++++-
3 files changed, 118 insertions(+), 1 deletion(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b36d08c..360656e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1629,5 +1629,22 @@ static inline unsigned int debug_guardpage_minorder(void) { return 0; }
static inline bool page_is_guard(struct page *page) { return false; }
#endif /* CONFIG_DEBUG_PAGEALLOC */
+#if (defined(CONFIG_VIRTIO_BALLOON) || \
+ defined(CONFIG_VIRTIO_BALLOON_MODULE)) && defined(CONFIG_COMPACTION)
+extern int is_balloon_page(struct page *);
+extern int isolate_balloon_page(struct page *);
+extern int putback_balloon_page(struct page *);
+
+/* return 1 if page is part of a guest's memory balloon, 0 otherwise */
+static inline int PageBalloon(struct page *page)
+{
+ return is_balloon_page(page);
+}
+#else
+static inline int PageBalloon(struct page *page) { return 0; }
+static inline int isolate_balloon_page(struct page *page) { return 0; }
+static inline int putback_balloon_page(struct page *page) { return 0; }
+#endif /* (VIRTIO_BALLOON || VIRTIO_BALLOON_MODULE) && COMPACTION */
+
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */
diff --git a/mm/compaction.c b/mm/compaction.c
index 7ea259d..8835d55 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -14,6 +14,7 @@
#include <linux/backing-dev.h>
#include <linux/sysctl.h>
#include <linux/sysfs.h>
+#include <linux/export.h>
#include "internal.h"
#if defined CONFIG_COMPACTION || defined CONFIG_CMA
@@ -312,6 +313,14 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
continue;
}
+ /*
+ * For ballooned pages, we need to isolate them before testing
+ * for PageLRU, as well as skip the LRU page isolation steps.
+ */
+ if (PageBalloon(page))
+ if (isolate_balloon_page(page))
+ goto isolated_balloon_page;
+
if (!PageLRU(page))
continue;
@@ -338,6 +347,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
/* Successfully isolated */
del_page_from_lru_list(page, lruvec, page_lru(page));
+isolated_balloon_page:
list_add(&page->lru, migratelist);
cc->nr_migratepages++;
nr_isolated++;
@@ -903,4 +913,66 @@ void compaction_unregister_node(struct node *node)
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */
+#if defined(CONFIG_VIRTIO_BALLOON) || defined(CONFIG_VIRTIO_BALLOON_MODULE)
+/*
+ * Balloon pages special page->mapping.
+ * users must properly allocate and initiliaze an instance of balloon_mapping,
+ * and set it as the page->mapping for balloon enlisted page instances.
+ *
+ * address_space_operations necessary methods for ballooned pages:
+ * .migratepage - used to perform balloon's page migration (as is)
+ * .invalidatepage - used to isolate a page from balloon's page list
+ * .freepage - used to reinsert an isolated page to balloon's page list
+ */
+struct address_space *balloon_mapping;
+EXPORT_SYMBOL(balloon_mapping);
+
+/* ballooned page id check */
+int is_balloon_page(struct page *page)
+{
+ struct address_space *mapping = page->mapping;
+ if (mapping == balloon_mapping)
+ return 1;
+ return 0;
+}
+
+/* __isolate_lru_page() counterpart for a ballooned page */
+int isolate_balloon_page(struct page *page)
+{
+ struct address_space *mapping = page->mapping;
+ if (mapping->a_ops->invalidatepage) {
+ /*
+ * We can race against move_to_new_page() and stumble across a
+ * locked 'newpage'. If we succeed on isolating it, the result
+ * tends to be disastrous. So, we sanely skip PageLocked here.
+ */
+ if (likely(!PageLocked(page) && get_page_unless_zero(page))) {
+ /*
+ * A ballooned page, by default, has just one refcount.
+ * Prevent concurrent compaction threads from isolating
+ * an already isolated balloon page.
+ */
+ if (page_count(page) == 2) {
+ mapping->a_ops->invalidatepage(page, 0);
+ return 1;
+ }
+ /* Drop refcount taken for this already isolated page */
+ put_page(page);
+ }
+ }
+ return 0;
+}
+
+/* putback_lru_page() counterpart for a ballooned page */
+int putback_balloon_page(struct page *page)
+{
+ struct address_space *mapping = page->mapping;
+ if (mapping->a_ops->freepage) {
+ mapping->a_ops->freepage(page);
+ put_page(page);
+ return 1;
+ }
+ return 0;
+}
+#endif /* CONFIG_VIRTIO_BALLOON || CONFIG_VIRTIO_BALLOON_MODULE */
#endif /* CONFIG_COMPACTION */
diff --git a/mm/migrate.c b/mm/migrate.c
index be26d5c..ffc02a4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -78,7 +78,10 @@ void putback_lru_pages(struct list_head *l)
list_del(&page->lru);
dec_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
- putback_lru_page(page);
+ if (unlikely(PageBalloon(page)))
+ VM_BUG_ON(!putback_balloon_page(page));
+ else
+ putback_lru_page(page);
}
}
@@ -783,6 +786,17 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
}
}
+ if (PageBalloon(page)) {
+ /*
+ * A ballooned page does not need any special attention from
+ * physical to virtual reverse mapping procedures.
+ * To avoid burning cycles at rmap level,
+ * skip attempts to unmap PTEs or remap swapcache.
+ */
+ remap_swapcache = 0;
+ goto skip_unmap;
+ }
+
/*
* Corner case handling:
* 1. When a new swap-cache page is read into, it is added to the LRU
@@ -852,6 +866,20 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
goto out;
rc = __unmap_and_move(page, newpage, force, offlining, mode);
+
+ if (PageBalloon(newpage)) {
+ /*
+ * A ballooned page has been migrated already. Now, it is the
+ * time to wrap-up counters, handle the old page back to Buddy
+ * and return.
+ */
+ list_del(&page->lru);
+ dec_zone_page_state(page, NR_ISOLATED_ANON +
+ page_is_file_cache(page));
+ put_page(page);
+ __free_page(page);
+ return rc;
+ }
out:
if (rc != -EAGAIN) {
/*
--
1.7.10.2
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