virtio-mem: Better retry handling

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).

Tested-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
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>
Link: https://lore.kernel.org/r/20200507140139.17083-11-david@redhat.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index a2edb87e5ed8641460e513c3028167c0328f7ba3..eb4c16d634e0d68c5640ddaf1d0d1d057fbaffb8 100644 (file)
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -141,7 +141,9 @@ 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;
@@ -1550,6 +1552,7 @@ retry:
 
        switch (rc) {
        case 0:
+               vm->retry_timer_ms = VIRTIO_MEM_RETRY_TIMER_MIN_MS;
                break;
        case -ENOSPC:
                /*
@@ -1565,8 +1568,7 @@ retry:
                 */
        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:
@@ -1586,6 +1588,8 @@ 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;
 }
 
@@ -1754,6 +1758,7 @@ 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);