On Tue, 27 Aug 2024 11:38:45 +0800, Jason Wang <jasow...@redhat.com> wrote: > On Tue, Aug 20, 2024 at 3:19 PM Xuan Zhuo <xuanz...@linux.alibaba.com> wrote: > > > > leads to regression on VM with the sysctl value of: > > > > - net.core.high_order_alloc_disable=1 > > > > which could see reliable crashes or scp failure (scp a file 100M in size > > to VM): > > > > The issue is that the virtnet_rq_dma takes up 16 bytes at the beginning > > of a new frag. When the frag size is larger than PAGE_SIZE, > > everything is fine. However, if the frag is only one page and the > > total size of the buffer and virtnet_rq_dma is larger than one page, an > > overflow may occur. In this case, if an overflow is possible, I adjust > > the buffer size. If net.core.high_order_alloc_disable=1, the maximum > > buffer size is 4096 - 16. If net.core.high_order_alloc_disable=0, only > > the first buffer of the frag is affected. > > I wonder instead of trying to make use of headroom, would it be > simpler if we allocate dedicated arrays of virtnet_rq_dma?
Sorry for the late reply. My mailbox was full, so I missed the reply to this thread. Thanks to Si-Wei for reminding me. If the virtnet_rq_dma is at the headroom, we can get the virtnet_rq_dma by buf. struct page *page = virt_to_head_page(buf); head = page_address(page); If we use a dedicated array, then we need pass the virtnet_rq_dma pointer to virtio core, the array has the same size with the rx ring. The virtnet_rq_dma will be: struct virtnet_rq_dma { dma_addr_t addr; u32 ref; u16 len; u16 need_sync; + void *buf; }; That will be simpler. > > Btw, I see it has a need_sync, I wonder if it can help for performance > or not? If not, any reason to keep that? I think yes, we can skip the cpu sync when we do not need it. Thanks. > > > > > Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever > > use_dma_api") > > Reported-by: "Si-Wei Liu" <si-wei....@oracle.com> > > Closes: > > http://lore.kernel.org/all/8b20cc28-45a9-4643-8e87-ba164a540...@oracle.com > > Signed-off-by: Xuan Zhuo <xuanz...@linux.alibaba.com> > > --- > > drivers/net/virtio_net.c | 12 +++++++++--- > > 1 file changed, 9 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index c6af18948092..e5286a6da863 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -918,9 +918,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, > > u32 size, gfp_t gfp) > > void *buf, *head; > > dma_addr_t addr; > > > > - if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp))) > > - return NULL; > > - > > head = page_address(alloc_frag->page); > > > > dma = head; > > @@ -2421,6 +2418,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, > > struct receive_queue *rq, > > len = SKB_DATA_ALIGN(len) + > > SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); > > > > + if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp))) > > + return -ENOMEM; > > + > > buf = virtnet_rq_alloc(rq, len, gfp); > > if (unlikely(!buf)) > > return -ENOMEM; > > @@ -2521,6 +2521,12 @@ static int add_recvbuf_mergeable(struct virtnet_info > > *vi, > > */ > > len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room); > > > > + if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp))) > > + return -ENOMEM; > > + > > + if (!alloc_frag->offset && len + room + sizeof(struct > > virtnet_rq_dma) > alloc_frag->size) > > + len -= sizeof(struct virtnet_rq_dma); > > + > > buf = virtnet_rq_alloc(rq, len + room, gfp); > > if (unlikely(!buf)) > > return -ENOMEM; > > -- > > 2.32.0.3.g01195cf9f > > Thanks > > > > > >