[PATCH v1] vhost: avoid large order allocations

[Michael Mueller]

From: Dong Dong Chen <ddongch@xxxxxxxxxx>

Under memory pressure we observe load issues with module vhost_net, as the
vhost setup code will try to do an order 4 allocation for the device.
The likeliness of this issue to occur can be reduced when the statically
allocated variable "iov" in "struct vhost_virtqueue" is dynamically allocated
with exactly the required size, reducing this to an order 2 allocation.

Signed-off-by: Dong Dong Chen <ddongch@xxxxxxxxxx>
Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Reviewed-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
Reviewed-by: Michael Mueller <mimu@xxxxxxxxxxxxxxxxxx>
---
 drivers/vhost/net.c   | 4 ++--
 drivers/vhost/scsi.c  | 4 ++--
 drivers/vhost/test.c  | 2 +-
 drivers/vhost/vhost.c | 6 +++++-
 drivers/vhost/vhost.h | 2 +-
 5 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index be414d2..e3a9a68 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -374,7 +374,7 @@ static void handle_tx(struct vhost_net *net)
 			break;
 
 		head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
-					 ARRAY_SIZE(vq->iov),
+					 UIO_MAXIOV,
 					 &out, &in,
 					 NULL, NULL);
 		/* On error, stop handling until the next kick. */
@@ -506,7 +506,7 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 			goto err;
 		}
 		r = vhost_get_vq_desc(vq->dev, vq, vq->iov + seg,
-				      ARRAY_SIZE(vq->iov) - seg, &out,
+				      UIO_MAXIOV - seg, &out,
 				      &in, log, log_num);
 		if (unlikely(r < 0))
 			goto err;
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index cf50ce9..a70f1d9 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -607,7 +607,7 @@ tcm_vhost_do_evt_work(struct vhost_scsi *vs, struct tcm_vhost_evt *evt)
 again:
 	vhost_disable_notify(&vs->dev, vq);
 	head = vhost_get_vq_desc(&vs->dev, vq, vq->iov,
-			ARRAY_SIZE(vq->iov), &out, &in,
+			UIO_MAXIOV, &out, &in,
 			NULL, NULL);
 	if (head < 0) {
 		vs->vs_events_missed = true;
@@ -946,7 +946,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 
 	for (;;) {
 		head = vhost_get_vq_desc(&vs->dev, vq, vq->iov,
-					ARRAY_SIZE(vq->iov), &out, &in,
+					UIO_MAXIOV, &out, &in,
 					NULL, NULL);
 		pr_debug("vhost_get_vq_desc: head: %d, out: %u in: %u\n",
 					head, out, in);
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index c2a54fb..2e01920 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -54,7 +54,7 @@ static void handle_vq(struct vhost_test *n)
 
 	for (;;) {
 		head = vhost_get_vq_desc(&n->dev, vq, vq->iov,
-					 ARRAY_SIZE(vq->iov),
+					 UIO_MAXIOV,
 					 &out, &in,
 					 NULL, NULL);
 		/* On error, stop handling until the next kick. */
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 78987e4..9017a55 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -251,6 +251,8 @@ static int vhost_worker(void *data)
 
 static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
 {
+	kfree(vq->iov);
+	vq->iov = NULL;
 	kfree(vq->indirect);
 	vq->indirect = NULL;
 	kfree(vq->log);
@@ -267,11 +269,12 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
 
 	for (i = 0; i < dev->nvqs; ++i) {
 		vq = dev->vqs[i];
+		vq->iov = kmalloc(sizeof(*vq->iov) * UIO_MAXIOV, GFP_KERNEL);
 		vq->indirect = kmalloc(sizeof *vq->indirect * UIO_MAXIOV,
 				       GFP_KERNEL);
 		vq->log = kmalloc(sizeof *vq->log * UIO_MAXIOV, GFP_KERNEL);
 		vq->heads = kmalloc(sizeof *vq->heads * UIO_MAXIOV, GFP_KERNEL);
-		if (!vq->indirect || !vq->log || !vq->heads)
+		if (!vq->iov || !vq->indirect || !vq->log || !vq->heads)
 			goto err_nomem;
 	}
 	return 0;
@@ -310,6 +313,7 @@ void vhost_dev_init(struct vhost_dev *dev,
 	for (i = 0; i < dev->nvqs; ++i) {
 		vq = dev->vqs[i];
 		vq->log = NULL;
+		vq->iov = NULL;
 		vq->indirect = NULL;
 		vq->heads = NULL;
 		vq->dev = dev;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 35eeb2a..541f757 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -100,7 +100,7 @@ struct vhost_virtqueue {
 	bool log_used;
 	u64 log_addr;
 
-	struct iovec iov[UIO_MAXIOV];
+	struct iovec *iov;
 	struct iovec *indirect;
 	struct vring_used_elem *heads;
 	/* Protected by virtqueue mutex. */
-- 
1.8.3.1

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