Re: [PATCH net-next 2/2] virtio-net: fix the XDP truesize calculation for mergeable buffers
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2020-05-06 07:37:51
Also in:
bpf, lkml, virtualization
On Wed, May 06, 2020 at 02:16:33PM +0800, Jason Wang wrote:
We should not exclude headroom and tailroom when XDP is set. So this patch fixes this by initializing the truesize from PAGE_SIZE when XDP is set. Cc: Jesper Dangaard Brouer <redacted> Signed-off-by: Jason Wang <jasowang@redhat.com>
Seems too aggressive, we do not use up the whole page for the size.
quoted hunk ↗ jump to hunk
--- drivers/net/virtio_net.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 98dd75b665a5..3f3aa8308918 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c@@ -1184,7 +1184,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi, char *buf; void *ctx; int err; - unsigned int len, hole; + unsigned int len, hole, truesize; /* Extra tailroom is needed to satisfy XDP's assumption. This * means rx frags coalescing won't work, but consider we've@@ -1194,6 +1194,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi, if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp))) return -ENOMEM; + truesize = headroom ? PAGE_SIZE : len; buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset; buf += headroom; /* advance address leaving hole at front of pkt */ get_page(alloc_frag->page);
Is this really just on the XDP path? Looks like a confusing way to detect that.
quoted hunk ↗ jump to hunk
@@ -1205,11 +1206,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi, * the current buffer. */ len += hole; + truesize += hole; alloc_frag->offset += hole; } sg_init_one(rq->sg, buf, len); - ctx = mergeable_len_to_ctx(len, headroom); + ctx = mergeable_len_to_ctx(truesize, headroom); err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp); if (err < 0) put_page(virt_to_head_page(buf));-- 2.20.1