3 files changed, 60 insertions, 46 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-xen-blkback b/Documentation/ABI/testing/sysfs-driver-xen-blkback
index 8bb43b66eb55..4e7babb3ba1f 100644
--- a/Documentation/ABI/testing/sysfs-driver-xen-blkback
+++ b/Documentation/ABI/testing/sysfs-driver-xen-blkback
@@ -15,3 +15,13 @@ Description:
                 blkback. If the frontend tries to use more than
                 max_persistent_grants, the LRU kicks in and starts
                 removing 5% of max_persistent_grants every 100ms.
+
+What:           /sys/module/xen_blkback/parameters/persistent_grant_unused_seconds
+Date:           August 2018
+KernelVersion:  4.19
+Contact:        Roger Pau Monné <roger.pau@citrix.com>
+Description:
+                How long a persistent grant is allowed to remain
+                allocated without being in use. The time is in
+                seconds, 0 means indefinitely long.
+                The default is 60 seconds.
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;