On 07/08/18 16:14, Roger Pau Monné wrote:

On Tue, Aug 07, 2018 at 08:31:31AM +0200, Juergen Gross wrote:

quoted

On 06/08/18 18:16, Roger Pau Monné wrote:

quoted

On Mon, Aug 06, 2018 at 01:34:01PM +0200, Juergen Gross wrote:

quoted

Add a periodic cleanup function to remove old persistent grants which
are no longer in use on the backend side. This avoids starvation in
case there are lots of persistent grants for a device which no longer
is involved in I/O business.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 drivers/block/xen-blkfront.c | 99 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 4 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index b5cedccb5d7d..19feb8835fc4 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c

@@ -46,6 +46,7 @@
 #include <linux/scatterlist.h>
 #include <linux/bitmap.h>
 #include <linux/list.h>
+#include <linux/workqueue.h>
 
 #include <xen/xen.h>
 #include <xen/xenbus.h>

@@ -121,6 +122,9 @@ static inline struct blkif_req *blkif_req(struct request *rq)
 
 static DEFINE_MUTEX(blkfront_mutex);
 static const struct block_device_operations xlvbd_block_fops;
+static struct delayed_work blkfront_work;
+static LIST_HEAD(info_list);
+static bool blkfront_work_active;
 
 /*
  * Maximum number of segments in indirect requests, the actual value used by

@@ -216,6 +220,7 @@ struct blkfront_info
 	/* Save uncomplete reqs and bios for migration. */
 	struct list_head requests;
 	struct bio_list bio_list;
+	struct list_head info_list;
 };
 
 static unsigned int nr_minors;

@@ -1764,6 +1769,12 @@ static int write_per_ring_nodes(struct xenbus_transaction xbt,
 	return err;
 }
 
+static void free_info(struct blkfront_info *info)
+{
+	list_del(&info->info_list);
+	kfree(info);
+}
+
 /* Common code used when first setting up, and when resuming. */
 static int talk_to_blkback(struct xenbus_device *dev,
 			   struct blkfront_info *info)

@@ -1885,7 +1896,10 @@ static int talk_to_blkback(struct xenbus_device *dev,
  destroy_blkring:
 	blkif_free(info, 0);
 
-	kfree(info);
+	mutex_lock(&blkfront_mutex);
+	free_info(info);
+	mutex_unlock(&blkfront_mutex);
+
 	dev_set_drvdata(&dev->dev, NULL);
 
 	return err;

@@ -1996,6 +2010,10 @@ static int blkfront_probe(struct xenbus_device *dev,
 	info->handle = simple_strtoul(strrchr(dev->nodename, '/')+1, NULL, 0);
 	dev_set_drvdata(&dev->dev, info);
 
+	mutex_lock(&blkfront_mutex);
+	list_add(&info->info_list, &info_list);
+	mutex_unlock(&blkfront_mutex);
+
 	return 0;
 }
 

@@ -2306,6 +2324,15 @@ static void blkfront_gather_backend_features(struct blkfront_info *info)
 	if (indirect_segments <= BLKIF_MAX_SEGMENTS_PER_REQUEST)
 		indirect_segments = 0;
 	info->max_indirect_segments = indirect_segments;
+
+	if (info->feature_persistent) {
+		mutex_lock(&blkfront_mutex);
+		if (!blkfront_work_active) {
+			blkfront_work_active = true;
+			schedule_delayed_work(&blkfront_work, HZ * 10);

Does it make sense to provide a module parameter to rune the schedule
of the cleanup routine?

I don't think this is something anyone would like to tune.

In case you think it should be tunable I can add a parameter, of course.

We can always add it later if required. I'm fine as-is now.

quoted

quoted

quoted

+		}
+		mutex_unlock(&blkfront_mutex);

Is it really necessary to have the blkfront_work_active boolean? What
happens if you queue the same delayed work more than once?

In case there is already work queued later calls of
schedule_delayed_work() will be ignored.

So yes, I can drop the global boolean (I still need a local flag in
blkfront_delay_work() for controlling the need to call
schedule_delayed_work() again).

Can't you just call schedule_delayed_work if info->feature_persistent
is set, even if that means calling it multiple times if multiple
blkfront instances are using persistent grants?

I don't like that. With mq we have a high chance for multiple instances
to use persistent grants and a local bool is much cheaper than unneeded
calls of schedule_delayed_work().


Juergen