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Subject: Re: [PATCH v14 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG

On 08/18/2017 10:22 AM, Michael S. Tsirkin wrote:
+static void send_balloon_page_sg(struct virtio_balloon *vb,
+				 struct virtqueue *vq,
+				 void *addr,
+				 uint32_t size)
+	unsigned int len;
+	int ret;
+	do {
+		ret = add_one_sg(vq, addr, size);
+		virtqueue_kick(vq);
+		wait_event(vb->acked, virtqueue_get_buf(vq, &len));
+		/*
+		 * It is uncommon to see the vq is full, because the sg is sent
+		 * one by one and the device is able to handle it in time. But
+		 * if that happens, we go back to retry after an entry gets
+		 * released.
+		 */
Why send one by one though? Why not batch some s/gs and wait for all
of them to be completed? If memory if fragmented, waiting every time is
worse than what we have now (VIRTIO_BALLOON_ARRAY_PFNS_MAX at a time).

OK, I'll do batching in some fashion.


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