[PATCH v2 09/10] virtio-mem: Better retry handling

From: David Hildenbrand <david@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, virtio-dev@lists.oasis-open.org,
	virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
	Michal Hocko <mhocko@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	David Hildenbrand <david@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Oscar Salvador <osalvador@suse.de>,
	Igor Mammedov <imammedo@redhat.com>,
	Dave Young <dyoung@redhat.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Vlastimil Babka <vbabka@suse.cz>
Subject: [PATCH v2 09/10] virtio-mem: Better retry handling
Date: Wed, 11 Mar 2020 18:14:21 +0100	[thread overview]
Message-ID: <20200311171422.10484-10-david@redhat.com> (raw)
In-Reply-To: <20200311171422.10484-1-david@redhat.com>

Let's start with a retry interval of 5 seconds and double the time until
we reach 5 minutes, in case we keep getting errors. Reset the retry
interval in case we succeeded.

The two main reasons for having to retry are
- The hypervisor is busy and cannot process our request
- We cannot reach the desired requested_size (esp., not enough memory can
  get unplugged because we can't allocate any subblocks).

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 drivers/virtio/virtio_mem.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index aa322e7732a4..48e96702d4ce 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -138,7 +138,9 @@ struct virtio_mem {
 
 	/* Timer for retrying to plug/unplug memory. */
 	struct hrtimer retry_timer;
-#define VIRTIO_MEM_RETRY_TIMER_MS		30000
+	unsigned int retry_timer_ms;
+#define VIRTIO_MEM_RETRY_TIMER_MIN_MS		50000
+#define VIRTIO_MEM_RETRY_TIMER_MAX_MS		300000
 
 	/* Memory notifier (online/offline events). */
 	struct notifier_block memory_notifier;
@@ -1548,6 +1550,7 @@ static void virtio_mem_run_wq(struct work_struct *work)
 
 	switch (rc) {
 	case 0:
+		vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
 		break;
 	case -ENOSPC:
 		/*
@@ -1563,8 +1566,7 @@ static void virtio_mem_run_wq(struct work_struct *work)
 		 */
 	case -ENOMEM:
 		/* Out of memory, try again later. */
-		hrtimer_start(&vm->retry_timer,
-			      ms_to_ktime(VIRTIO_MEM_RETRY_TIMER_MS),
+		hrtimer_start(&vm->retry_timer, ms_to_ktime(vm->retry_timer_ms),
 			      HRTIMER_MODE_REL);
 		break;
 	case -EAGAIN:
@@ -1584,6 +1586,8 @@ static enum hrtimer_restart virtio_mem_timer_expired(struct hrtimer *timer)
 					     retry_timer);
 
 	virtio_mem_retry(vm);
+	vm->retry_timer_ms = min_t(unsigned int, vm->retry_timer_ms * 2,
+				   VIRTIO_MEM_RETRY_TIMER_MAX_MS);
 	return HRTIMER_NORESTART;
 }
 
@@ -1750,6 +1754,7 @@ static int virtio_mem_probe(struct virtio_device *vdev)
 	spin_lock_init(&vm->removal_lock);
 	hrtimer_init(&vm->retry_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	vm->retry_timer.function = virtio_mem_timer_expired;
+	vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
 
 	/* register the virtqueue */
 	rc = virtio_mem_init_vq(vm);
-- 
2.24.1

