2 files changed, 50 insertions, 46 deletions

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index b55b245e8052..9eae7b243f68 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -84,6 +84,18 @@ MODULE_PARM_DESC(max_persistent_grants,
                  "Maximum number of grants to map persistently");
 
 /*
+ * How long a persistent grant is allowed to remain allocated without being in
+ * use. The time is in seconds, 0 means indefinitely long.
+ */
+
+static unsigned int xen_blkif_pgrant_timeout = 60;
+module_param_named(persistent_grant_unused_seconds, xen_blkif_pgrant_timeout,
+		   uint, 0644);
+MODULE_PARM_DESC(persistent_grant_unused_seconds,
+		 "Time in seconds an unused persistent grant is allowed to "
+		 "remain allocated. Default is 60, 0 means unlimited.");
+
+/*
  * Maximum number of rings/queues blkback supports, allow as many queues as there
  * are CPUs if user has not specified a value.
  */
@@ -123,6 +135,13 @@ module_param(log_stats, int, 0644);
 /* Number of free pages to remove on each call to gnttab_free_pages */
 #define NUM_BATCH_FREE_PAGES 10
 
+static inline bool persistent_gnt_timeout(struct persistent_gnt *persistent_gnt)
+{
+	return xen_blkif_pgrant_timeout &&
+	       (jiffies - persistent_gnt->last_used >=
+		HZ * xen_blkif_pgrant_timeout);
+}
+
 static inline int get_free_page(struct xen_blkif_ring *ring, struct page **page)
 {
 	unsigned long flags;
@@ -278,7 +297,7 @@ static void put_persistent_gnt(struct xen_blkif_ring *ring,
 {
 	if(!test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags))
 		pr_alert_ratelimited("freeing a grant already unused\n");
-	set_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
+	persistent_gnt->last_used = jiffies;
 	clear_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags);
 	atomic_dec(&ring->persistent_gnt_in_use);
 }
@@ -371,26 +390,26 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring)
 	struct persistent_gnt *persistent_gnt;
 	struct rb_node *n;
 	unsigned int num_clean, total;
-	bool scan_used = false, clean_used = false;
+	bool scan_used = false;
 	struct rb_root *root;
 
-	if (ring->persistent_gnt_c < xen_blkif_max_pgrants ||
-	    (ring->persistent_gnt_c == xen_blkif_max_pgrants &&
-	    !ring->blkif->vbd.overflow_max_grants)) {
-		goto out;
-	}
-
 	if (work_busy(&ring->persistent_purge_work)) {
 		pr_alert_ratelimited("Scheduled work from previous purge is still busy, cannot purge list\n");
 		goto out;
 	}
 
-	num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN;
-	num_clean = ring->persistent_gnt_c - xen_blkif_max_pgrants + num_clean;
-	num_clean = min(ring->persistent_gnt_c, num_clean);
-	if ((num_clean == 0) ||
-	    (num_clean > (ring->persistent_gnt_c - atomic_read(&ring->persistent_gnt_in_use))))
-		goto out;
+	if (ring->persistent_gnt_c < xen_blkif_max_pgrants ||
+	    (ring->persistent_gnt_c == xen_blkif_max_pgrants &&
+	    !ring->blkif->vbd.overflow_max_grants)) {
+		num_clean = 0;
+	} else {
+		num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN;
+		num_clean = ring->persistent_gnt_c - xen_blkif_max_pgrants +
+			    num_clean;
+		num_clean = min(ring->persistent_gnt_c, num_clean);
+		pr_debug("Going to purge at least %u persistent grants\n",
+			 num_clean);
+	}
 
 	/*
 	 * At this point, we can assure that there will be no calls
@@ -401,9 +420,7 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring)
          * number of grants.
 	 */
 
-	total = num_clean;
-
-	pr_debug("Going to purge %u persistent grants\n", num_clean);
+	total = 0;
 
 	BUG_ON(!list_empty(&ring->persistent_purge_list));
 	root = &ring->persistent_gnts;
@@ -412,46 +429,37 @@ purge_list:
 		BUG_ON(persistent_gnt->handle ==
 			BLKBACK_INVALID_HANDLE);
 
-		if (clean_used) {
-			clear_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags);
-			continue;
-		}
-
 		if (test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags))
 			continue;
-		if (!scan_used &&
-		    (test_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags)))
+		if (!scan_used && !persistent_gnt_timeout(persistent_gnt))
+			continue;
+		if (scan_used && total >= num_clean)
 			continue;
 
 		rb_erase(&persistent_gnt->node, root);
 		list_add(&persistent_gnt->remove_node,
 			 &ring->persistent_purge_list);
-		if (--num_clean == 0)
-			goto finished;
+		total++;
 	}
 	/*
-	 * If we get here it means we also need to start cleaning
+	 * Check whether we also need to start cleaning
 	 * grants that were used since last purge in order to cope
 	 * with the requested num
 	 */
-	if (!scan_used && !clean_used) {
-		pr_debug("Still missing %u purged frames\n", num_clean);
+	if (!scan_used && total < num_clean) {
+		pr_debug("Still missing %u purged frames\n", num_clean - total);
 		scan_used = true;
 		goto purge_list;
 	}
-finished:
-	if (!clean_used) {
-		pr_debug("Finished scanning for grants to clean, removing used flag\n");
-		clean_used = true;
-		goto purge_list;
-	}
 
-	ring->persistent_gnt_c -= (total - num_clean);
-	ring->blkif->vbd.overflow_max_grants = 0;
+	if (total) {
+		ring->persistent_gnt_c -= total;
+		ring->blkif->vbd.overflow_max_grants = 0;
 
-	/* We can defer this work */
-	schedule_work(&ring->persistent_purge_work);
-	pr_debug("Purged %u/%u\n", (total - num_clean), total);
+		/* We can defer this work */
+		schedule_work(&ring->persistent_purge_work);
+		pr_debug("Purged %u/%u\n", num_clean, total);
+	}
 
 out:
 	return;
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index ecb35fe8ca8d..7bff72db3b7e 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -234,14 +234,9 @@ struct xen_vbd {
 struct backend_info;
 
 /* Number of available flags */
-#define PERSISTENT_GNT_FLAGS_SIZE	2
+#define PERSISTENT_GNT_FLAGS_SIZE	1
 /* This persistent grant is currently in use */
 #define PERSISTENT_GNT_ACTIVE		0
-/*
- * This persistent grant has been used, this flag is set when we remove the
- * PERSISTENT_GNT_ACTIVE, to know that this grant has been used recently.
- */
-#define PERSISTENT_GNT_WAS_ACTIVE	1
 
 /* Number of requests that we can fit in a ring */
 #define XEN_BLKIF_REQS_PER_PAGE		32
@@ -250,6 +245,7 @@ struct persistent_gnt {
 	struct page *page;
 	grant_ref_t gnt;
 	grant_handle_t handle;
+	unsigned long last_used;
 	DECLARE_BITMAP(flags, PERSISTENT_GNT_FLAGS_SIZE);
 	struct rb_node node;
 	struct list_head remove_node;