Re: [PATCH v1] vhost: avoid large order allocations
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2014-05-13 08:42:11
Also in:
kvm, lkml, virtualization
On Tue, May 13, 2014 at 10:35:33AM +0200, Michael Mueller wrote:
From: Dong Dong Chen <redacted> 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 <redacted> Reviewed-by: Christian Borntraeger <redacted> Reviewed-by: Cornelia Huck <redacted> Reviewed-by: Michael Mueller <redacted>
Please dont' do this, extra indirection hurts performance. Instead, please change vhost_net_open and scsi to allocate the whole structure with vmalloc if kmalloc fails, along the lines of 74d332c13b2148ae934ea94dac1745ae92efe8e5
quoted hunk ↗ jump to hunk
--- 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