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Message-ID: <20131223133106.GC18168@redhat.com>
Date: Mon, 23 Dec 2013 15:31:06 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Michael Dalton <mwdalton@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
Eric Dumazet <edumazet@...gle.com>,
Rusty Russell <rusty@...tcorp.com.au>,
Jason Wang <jasowang@...hat.com>,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next 2/3] virtio-net: use per-receive queue page frag
alloc for mergeable bufs
On Mon, Dec 16, 2013 at 04:16:28PM -0800, Michael Dalton wrote:
> The virtio-net driver currently uses netdev_alloc_frag() for GFP_ATOMIC
> mergeable rx buffer allocations. This commit migrates virtio-net to use
> per-receive queue page frags for GFP_ATOMIC allocation. This change unifies
> mergeable rx buffer memory allocation, which now will use skb_refill_frag()
> for both atomic and GFP-WAIT buffer allocations.
OK so just to clarify, this is intended as a cleanup
and preparation for 3/3, not as an optimization?
Some notes below.
>
> To address fragmentation concerns, if after buffer allocation there
> is too little space left in the page frag to allocate a subsequent
> buffer, the remaining space is added to the current allocated buffer
> so that the remaining space can be used to store packet data.
>
> Signed-off-by: Michael Dalton <mwdalton@...gle.com>
> ---
> drivers/net/virtio_net.c | 69 ++++++++++++++++++++++++++----------------------
> 1 file changed, 38 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c51a988..d38d130 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -78,6 +78,9 @@ struct receive_queue {
> /* Chain pages by the private ptr. */
> struct page *pages;
>
> + /* Page frag for GFP_ATOMIC packet buffer allocation. */
> + struct page_frag atomic_frag;
> +
> /* RX: fragments + linear part + virtio header */
> struct scatterlist sg[MAX_SKB_FRAGS + 2];
>
> @@ -127,9 +130,9 @@ struct virtnet_info {
> struct mutex config_lock;
>
> /* Page_frag for GFP_KERNEL packet buffer allocation when we run
> - * low on memory.
> + * low on memory. May sleep.
> */
> - struct page_frag alloc_frag;
> + struct page_frag sleep_frag;
>
> /* Does the affinity hint is set for virtqueues? */
> bool affinity_hint_set;
> @@ -336,8 +339,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> int num_buf = hdr->mhdr.num_buffers;
> struct page *page = virt_to_head_page(buf);
> int offset = buf - page_address(page);
> - struct sk_buff *head_skb = page_to_skb(rq, page, offset, len,
> - MERGE_BUFFER_LEN);
> + int truesize = max_t(int, len, MERGE_BUFFER_LEN);
> + struct sk_buff *head_skb = page_to_skb(rq, page, offset, len, truesize);
> struct sk_buff *curr_skb = head_skb;
>
> if (unlikely(!curr_skb))
> @@ -353,11 +356,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> dev->stats.rx_length_errors++;
> goto err_buf;
> }
> - if (unlikely(len > MERGE_BUFFER_LEN)) {
> - pr_debug("%s: rx error: merge buffer too long\n",
> - dev->name);
> - len = MERGE_BUFFER_LEN;
> - }
>
> page = virt_to_head_page(buf);
> --rq->num;
> @@ -376,19 +374,20 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> head_skb->truesize += nskb->truesize;
> num_skb_frags = 0;
> }
> + truesize = max_t(int, len, MERGE_BUFFER_LEN);
> if (curr_skb != head_skb) {
> head_skb->data_len += len;
> head_skb->len += len;
> - head_skb->truesize += MERGE_BUFFER_LEN;
> + head_skb->truesize += truesize;
> }
> offset = buf - page_address(page);
> if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
> put_page(page);
> skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
> - len, MERGE_BUFFER_LEN);
> + len, truesize);
> } else {
> skb_add_rx_frag(curr_skb, num_skb_frags, page,
> - offset, len, MERGE_BUFFER_LEN);
> + offset, len, truesize);
> }
> }
>
> @@ -579,24 +578,24 @@ static int add_recvbuf_big(struct receive_queue *rq, gfp_t gfp)
> static int add_recvbuf_mergeable(struct receive_queue *rq, gfp_t gfp)
> {
> struct virtnet_info *vi = rq->vq->vdev->priv;
> - char *buf = NULL;
> - int err;
> + struct page_frag *alloc_frag;
> + char *buf;
> + int err, len, hole;
>
> - if (gfp & __GFP_WAIT) {
> - if (skb_page_frag_refill(MERGE_BUFFER_LEN, &vi->alloc_frag,
> - gfp)) {
> - buf = (char *)page_address(vi->alloc_frag.page) +
> - vi->alloc_frag.offset;
> - get_page(vi->alloc_frag.page);
> - vi->alloc_frag.offset += MERGE_BUFFER_LEN;
> - }
> - } else {
> - buf = netdev_alloc_frag(MERGE_BUFFER_LEN);
> - }
> - if (!buf)
> + alloc_frag = (gfp & __GFP_WAIT) ? &vi->sleep_frag : &rq->atomic_frag;
> + if (unlikely(!skb_page_frag_refill(MERGE_BUFFER_LEN, alloc_frag, gfp)))
> return -ENOMEM;
I note that netdev_alloc_frag sets __GFP_COLD which kind of
makes sense.
I also note that netdev_alloc_frag uses some tricks to
reduce the amount of cache lines dirtied - need to look
at whether they actually apply here.
> + buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> + get_page(alloc_frag->page);
> + len = MERGE_BUFFER_LEN;
> + alloc_frag->offset += len;
> + hole = alloc_frag->size - alloc_frag->offset;
> + if (hole < MERGE_BUFFER_LEN) {
> + len += hole;
> + alloc_frag->offset += hole;
> + }
>
> - sg_init_one(rq->sg, buf, MERGE_BUFFER_LEN);
> + sg_init_one(rq->sg, buf, len);
> err = virtqueue_add_inbuf(rq->vq, rq->sg, 1, buf, gfp);
> if (err < 0)
> put_page(virt_to_head_page(buf));
> @@ -1377,6 +1376,16 @@ static void free_receive_bufs(struct virtnet_info *vi)
> }
> }
>
> +static void free_receive_page_frags(struct virtnet_info *vi)
> +{
> + int i;
> + for (i = 0; i < vi->max_queue_pairs; i++)
> + if (vi->rq[i].atomic_frag.page)
> + put_page(vi->rq[i].atomic_frag.page);
> + if (vi->sleep_frag.page)
> + put_page(vi->sleep_frag.page);
> +}
> +
> static void free_unused_bufs(struct virtnet_info *vi)
> {
> void *buf;
> @@ -1706,8 +1715,7 @@ free_recv_bufs:
> free_vqs:
> cancel_delayed_work_sync(&vi->refill);
> virtnet_del_vqs(vi);
> - if (vi->alloc_frag.page)
> - put_page(vi->alloc_frag.page);
> + free_receive_page_frags(vi);
> free_stats:
> free_percpu(vi->stats);
> free:
> @@ -1741,8 +1749,7 @@ static void virtnet_remove(struct virtio_device *vdev)
> unregister_netdev(vi->dev);
>
> remove_vq_common(vi);
> - if (vi->alloc_frag.page)
> - put_page(vi->alloc_frag.page);
> + free_receive_page_frags(vi);
>
> flush_work(&vi->config_work);
>
> --
> 1.8.5.1
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