linux-kernel - Re: [PATCH v14 3/5] virtio-balloon: VIRTIO_BALLOON_F

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Message-ID: <599699AF.1090705@intel.com>
Date:   Fri, 18 Aug 2017 15:39:27 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mhocko@...nel.org,
        akpm@...ux-foundation.org, mawilcox@...rosoft.com,
        david@...hat.com, cornelia.huck@...ibm.com,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com, willy@...radead.org,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu@...yun.com
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.


Best,
Wei