linux-kernel - RE: [PATCH v13 3/5] virtio-balloon: VIRTIO_BALLOON_F

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Date:   Thu, 3 Aug 2017 15:17:59 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "mawilcox@...rosoft.com" <mawilcox@...rosoft.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "david@...hat.com" <david@...hat.com>,
        "cornelia.huck@...ibm.com" <cornelia.huck@...ibm.com>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        "amit.shah@...hat.com" <amit.shah@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "liliang.opensource@...il.com" <liliang.opensource@...il.com>,
        "yang.zhang.wz@...il.com" <yang.zhang.wz@...il.com>,
        "quan.xu@...yun.com" <quan.xu@...yun.com>
Subject: RE: [PATCH v13 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG

On Thursday, August 3, 2017 10:23 PM, Michael S. Tsirkin wrote:
> On Thu, Aug 03, 2017 at 02:38:17PM +0800, Wei Wang wrote:
> > +static void send_one_sg(struct virtio_balloon *vb, struct virtqueue *vq,
> > +			void *addr, uint32_t size)
> > +{
> > +	struct scatterlist sg;
> > +	unsigned int len;
> > +
> > +	sg_init_one(&sg, addr, size);
> > +	while (unlikely(virtqueue_add_inbuf(vq, &sg, 1, vb, GFP_KERNEL)
> > +			== -ENOSPC)) {
> > +		/*
> > +		 * 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 kick and wait for an entry is released.
> 
> is released -> to get used.
> 
> > +		 */
> > +		virtqueue_kick(vq);
> > +		while (!virtqueue_get_buf(vq, &len) &&
> > +		       !virtqueue_is_broken(vq))
> > +			cpu_relax();
> 
> Please rework to use wait_event in that case too.

For the balloon page case here, it is fine to use wait_event. But for the free page
case, I think it might not be suitable because the mm lock is being held.

Best,
Wei