[PATCH v1] vhost: avoid large order allocations

Michael Mueller
2014-05-13T08:36:07Z

From: Dong Dong Chen <ddongch@cn.ibm.com>

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@cn.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: Michael Mueller <mimu@linux.vnet.ibm.com>
---
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