virtio: net refill on out-of-memory

If we run out of memory, use keventd to fill the buffer.  There's a
report of this happening: "Page allocation failures in guest",
Message-ID: <20090713115158.0a4892b0@mjolnir.ossman.eu>

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 46 insertions, 15 deletions

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 2a6e81d5b579..bbedf03a2124 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -70,6 +70,9 @@ struct virtnet_info
         struct sk_buff_head recv;
         struct sk_buff_head send;
 
+        /* Work struct for refilling if we run low on memory. */
+        struct delayed_work refill;
+
         /* Chain pages by the private ptr. */
         struct page *pages;
 };
@@ -273,19 +276,22 @@ drop:
         dev_kfree_skb(skb);
 }
 
-static void try_fill_recv_maxbufs(struct virtnet_info *vi)
+static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
 {
         struct sk_buff *skb;
         struct scatterlist sg[2+MAX_SKB_FRAGS];
         int num, err, i;
+        bool oom = false;
 
         sg_init_table(sg, 2+MAX_SKB_FRAGS);
         for (;;) {
                 struct virtio_net_hdr *hdr;
 
                 skb = netdev_alloc_skb(vi->dev, MAX_PACKET_LEN + NET_IP_ALIGN);
-                if (unlikely(!skb))
+                if (unlikely(!skb)) {
+                        oom = true;
                         break;
+                }
 
                 skb_reserve(skb, NET_IP_ALIGN);
                 skb_put(skb, MAX_PACKET_LEN);
@@ -296,7 +302,7 @@ static void try_fill_recv_maxbufs(struct virtnet_info *vi)
                 if (vi->big_packets) {
                         for (i = 0; i < MAX_SKB_FRAGS; i++) {
                                 skb_frag_t *f = &skb_shinfo(skb)->frags[i];
-                                f->page = get_a_page(vi, GFP_ATOMIC);
+                                f->page = get_a_page(vi, gfp);
                                 if (!f->page)
                                         break;
 
@@ -325,31 +331,35 @@ static void try_fill_recv_maxbufs(struct virtnet_info *vi)
         if (unlikely(vi->num > vi->max))
                 vi->max = vi->num;
         vi->rvq->vq_ops->kick(vi->rvq);
+        return !oom;
 }
 
-static void try_fill_recv(struct virtnet_info *vi)
+/* Returns false if we couldn't fill entirely (OOM). */
+static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
 {
         struct sk_buff *skb;
         struct scatterlist sg[1];
         int err;
+        bool oom = false;
 
-        if (!vi->mergeable_rx_bufs) {
-                try_fill_recv_maxbufs(vi);
-                return;
-        }
+        if (!vi->mergeable_rx_bufs)
+                return try_fill_recv_maxbufs(vi, gfp);
 
         for (;;) {
                 skb_frag_t *f;
 
                 skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN);
-                if (unlikely(!skb))
+                if (unlikely(!skb)) {
+                        oom = true;
                         break;
+                }
 
                 skb_reserve(skb, NET_IP_ALIGN);
 
                 f = &skb_shinfo(skb)->frags[0];
-                f->page = get_a_page(vi, GFP_ATOMIC);
+                f->page = get_a_page(vi, gfp);
                 if (!f->page) {
+                        oom = true;
                         kfree_skb(skb);
                         break;
                 }
@@ -373,6 +383,7 @@ static void try_fill_recv(struct virtnet_info *vi)
         if (unlikely(vi->num > vi->max))
                 vi->max = vi->num;
         vi->rvq->vq_ops->kick(vi->rvq);
+        return !oom;
 }
 
 static void skb_recv_done(struct virtqueue *rvq)
@@ -385,6 +396,23 @@ static void skb_recv_done(struct virtqueue *rvq)
         }
 }
 
+static void refill_work(struct work_struct *work)
+{
+        struct virtnet_info *vi;
+        bool still_empty;
+
+        vi = container_of(work, struct virtnet_info, refill.work);
+        napi_disable(&vi->napi);
+        try_fill_recv(vi, GFP_KERNEL);
+        still_empty = (vi->num == 0);
+        napi_enable(&vi->napi);
+
+        /* In theory, this can happen: if we don't get any buffers in
+         * we will *never* try to fill again. */
+        if (still_empty)
+                schedule_delayed_work(&vi->refill, HZ/2);
+}
+
 static int virtnet_poll(struct napi_struct *napi, int budget)
 {
         struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi);
@@ -400,10 +428,10 @@ again:
                 received++;
         }
 
-        /* FIXME: If we oom and completely run out of inbufs, we need
-         * to start a timer trying to fill more. */
-        if (vi->num < vi->max / 2)
-                try_fill_recv(vi);
+        if (vi->num < vi->max / 2) {
+                if (!try_fill_recv(vi, GFP_ATOMIC))
+                        schedule_delayed_work(&vi->refill, 0);
+        }
 
         /* Out of packets? */
         if (received < budget) {
@@ -893,6 +921,7 @@ static int virtnet_probe(struct virtio_device *vdev)
         vi->vdev = vdev;
         vdev->priv = vi;
         vi->pages = NULL;
+        INIT_DELAYED_WORK(&vi->refill, refill_work);
 
         /* If they give us a callback when all buffers are done, we don't need
          * the timer. */
@@ -941,7 +970,7 @@ static int virtnet_probe(struct virtio_device *vdev)
         }
 
         /* Last of all, set up some receive buffers. */
-        try_fill_recv(vi);
+        try_fill_recv(vi, GFP_KERNEL);
 
         /* If we didn't even get one input buffer, we're useless. */
         if (vi->num == 0) {
@@ -958,6 +987,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 unregister:
         unregister_netdev(dev);
+        cancel_delayed_work_sync(&vi->refill);
 free_vqs:
         vdev->config->del_vqs(vdev);
 free:
@@ -986,6 +1016,7 @@ static void virtnet_remove(struct virtio_device *vdev)
         BUG_ON(vi->num != 0);
 
         unregister_netdev(vi->dev);
+        cancel_delayed_work_sync(&vi->refill);
 
         vdev->config->del_vqs(vi->vdev);