Date:   Wed, 17 Jan 2018 17:00:11 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Pankaj Gupta <pagupta@...hat.com>
CC:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mst@...hat.com, mhocko@...nel.org,
        akpm@...ux-foundation.org, pbonzini@...hat.com,
        liliang opensource <liliang.opensource@...il.com>,
        yang zhang wz <yang.zhang.wz@...il.com>,
        quan xu0 <quan.xu0@...il.com>, nilal@...hat.com,
        riel@...hat.com
Subject: Re: [PATCH v22 2/3] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ

On 01/17/2018 04:21 PM, Pankaj Gupta wrote:
>> Negotiation of the VIRTIO_BALLOON_F_FREE_PAGE_VQ feature indicates the
>> support of reporting hints of guest free pages to host via virtio-balloon.
>>
>> Host requests the guest to report free pages by sending a new cmd
>> id to the guest via the free_page_report_cmd_id configuration register.
>>
>> When the guest starts to report, the first element added to the free page
>> vq is the cmd id given by host. When the guest finishes the reporting
>> of all the free pages, VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID is added
>> to the vq to tell host that the reporting is done. Host may also requests
>> the guest to stop the reporting in advance by sending the stop cmd id to
>> the guest via the configuration register.
>>
>> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
>> Signed-off-by: Liang Li <liang.z.li@...el.com>
>> Cc: Michael S. Tsirkin <mst@...hat.com>
>> Cc: Michal Hocko <mhocko@...nel.org>
>> ---
>>   drivers/virtio/virtio_balloon.c     | 242
>>   +++++++++++++++++++++++++++++++-----
>>   include/uapi/linux/virtio_balloon.h |   4 +
>>   2 files changed, 214 insertions(+), 32 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_balloon.c
>> b/drivers/virtio/virtio_balloon.c
>> index a1fb52c..b9561a5 100644
>> --- a/drivers/virtio/virtio_balloon.c
>> +++ b/drivers/virtio/virtio_balloon.c
>> @@ -53,7 +53,12 @@ static struct vfsmount *balloon_mnt;
>>   
>>   struct virtio_balloon {
>>   	struct virtio_device *vdev;
>> -	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
>> +	struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
>> +
>> +	/* Balloon's own wq for cpu-intensive work items */
>> +	struct workqueue_struct *balloon_wq;
>> +	/* The free page reporting work item submitted to the balloon wq */
>> +	struct work_struct report_free_page_work;
>>   
>>   	/* The balloon servicing is delegated to a freezable workqueue. */
>>   	struct work_struct update_balloon_stats_work;
>> @@ -63,6 +68,13 @@ struct virtio_balloon {
>>   	spinlock_t stop_update_lock;
>>   	bool stop_update;
>>   
>> +	/* Start to report free pages */
>> +	bool report_free_page;
>> +	/* Stores the cmd id given by host to start the free page reporting */
>> +	uint32_t start_cmd_id;
>> +	/* Stores STOP_ID as a sign to tell host that the reporting is done */
>> +	uint32_t stop_cmd_id;
>> +
>>   	/* Waiting for host to ack the pages we released. */
>>   	wait_queue_head_t acked;
>>   
>> @@ -281,6 +293,71 @@ static unsigned int update_balloon_stats(struct
>> virtio_balloon *vb)
>>   	return idx;
>>   }
>>   
>> +static void add_one_sg(struct virtqueue *vq, unsigned long pfn, uint32_t
>> len)
>> +{
>> +	struct scatterlist sg;
>> +	unsigned int unused;
>> +	int err;
>> +
>> +	sg_init_table(&sg, 1);
>> +	sg_set_page(&sg, pfn_to_page(pfn), len, 0);
>> +
>> +	/* Detach all the used buffers from the vq */
>> +	while (virtqueue_get_buf(vq, &unused))
>> +		;
>> +
>> +	/*
>> +	 * Since this is an optimization feature, losing a couple of free
>> +	 * pages to report isn't important. We simply resturn without adding
>> +	 * the page if the vq is full. We are adding one entry each time,
>> +	 * which essentially results in no memory allocation, so the
>> +	 * GFP_KERNEL flag below can be ignored.
>> +	 */
>> +	if (vq->num_free) {
>> +		err = virtqueue_add_inbuf(vq, &sg, 1, vq, GFP_KERNEL);
>> +		/*
>> +		 * This is expected to never fail, because there is always an
>> +		 * entry available on the vq.
>> +		 */
>> +		BUG_ON(err);
>> +	}
>> +}
>> +
>> +static void batch_free_page_sg(struct virtqueue *vq,
>> +			       unsigned long pfn,
>> +			       uint32_t len)
>> +{
>> +	add_one_sg(vq, pfn, len);
>> +
>> +	/* Batch till the vq is full */
>> +	if (!vq->num_free)
>> +		virtqueue_kick(vq);
>> +}
>> +
>> +static void send_cmd_id(struct virtqueue *vq, void *addr)
>> +{
>> +	struct scatterlist sg;
>> +	unsigned int unused;
>> +	int err;
>> +
>> +	sg_init_one(&sg, addr, sizeof(uint32_t));
>> +
>> +	/*
>> +	 * This handles the cornercase that the vq happens to be full when
>> +	 * adding a cmd id. Rarely happen in practice.
>> +	 */
>> +	while (!vq->num_free)
>> +		virtqueue_get_buf(vq, &unused);
>> +
>> +	err = virtqueue_add_outbuf(vq, &sg, 1, vq, GFP_KERNEL);
>> +	/*
>> +	 * This is expected to never fail, because there is always an
>> +	 * entry available on the vq.
>> +	 */
>> +	BUG_ON(err);
>> +	virtqueue_kick(vq);
>> +}
>> +
>>   /*
>>    * While most virtqueues communicate guest-initiated requests to the
>>    hypervisor,
>>    * the stats queue operates in reverse.  The driver initializes the
>>    virtqueue
>> @@ -316,17 +393,6 @@ static void stats_handle_request(struct virtio_balloon
>> *vb)
>>   	virtqueue_kick(vq);
>>   }
>>   
>> -static void virtballoon_changed(struct virtio_device *vdev)
>> -{
>> -	struct virtio_balloon *vb = vdev->priv;
>> -	unsigned long flags;
>> -
>> -	spin_lock_irqsave(&vb->stop_update_lock, flags);
>> -	if (!vb->stop_update)
>> -		queue_work(system_freezable_wq, &vb->update_balloon_size_work);
>> -	spin_unlock_irqrestore(&vb->stop_update_lock, flags);
>> -}
>> -
>>   static inline s64 towards_target(struct virtio_balloon *vb)
>>   {
>>   	s64 target;
>> @@ -343,6 +409,36 @@ static inline s64 towards_target(struct virtio_balloon
>> *vb)
>>   	return target - vb->num_pages;
>>   }
>>   
>> +static void virtballoon_changed(struct virtio_device *vdev)
>> +{
>> +	struct virtio_balloon *vb = vdev->priv;
>> +	unsigned long flags;
>> +	__u32 cmd_id;
>> +	s64 diff = towards_target(vb);
>> +
>> +	if (diff) {
>> +		spin_lock_irqsave(&vb->stop_update_lock, flags);
>> +		if (!vb->stop_update)
>> +			queue_work(system_freezable_wq,
>> +				   &vb->update_balloon_size_work);
>> +		spin_unlock_irqrestore(&vb->stop_update_lock, flags);
>> +	}
>> +
>> +	virtio_cread(vb->vdev, struct virtio_balloon_config,
>> +		     free_page_report_cmd_id, &cmd_id);
>> +	if (cmd_id == VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID) {
>> +		WRITE_ONCE(vb->report_free_page, false);
>> +	} else if (cmd_id != vb->start_cmd_id) {
>> +		/*
>> +		 * Host requests to start the reporting by sending a new cmd
>> +		 * id.
>> +		 */
>> +		WRITE_ONCE(vb->report_free_page, true);
>> +		vb->start_cmd_id = cmd_id;
>> +		queue_work(vb->balloon_wq, &vb->report_free_page_work);
>> +	}
>> +}
>> +
>>   static void update_balloon_size(struct virtio_balloon *vb)
>>   {
>>   	u32 actual = vb->num_pages;
>> @@ -417,40 +513,113 @@ static void update_balloon_size_func(struct
>> work_struct *work)
>>   
>>   static int init_vqs(struct virtio_balloon *vb)
>>   {
>> -	struct virtqueue *vqs[3];
>> -	vq_callback_t *callbacks[] = { balloon_ack, balloon_ack, stats_request };
>> -	static const char * const names[] = { "inflate", "deflate", "stats" };
>> -	int err, nvqs;
>> +	struct virtqueue **vqs;
>> +	vq_callback_t **callbacks;
>> +	const char **names;
>> +	struct scatterlist sg;
>> +	int i, nvqs, err = -ENOMEM;
>> +
>> +	/* Inflateq and deflateq are used unconditionally */
>> +	nvqs = 2;
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ))
>> +		nvqs++;
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ))
>> +		nvqs++;
>> +
>> +	/* Allocate space for find_vqs parameters */
>> +	vqs = kcalloc(nvqs, sizeof(*vqs), GFP_KERNEL);
>> +	if (!vqs)
>> +		goto err_vq;
>> +	callbacks = kmalloc_array(nvqs, sizeof(*callbacks), GFP_KERNEL);
>> +	if (!callbacks)
>> +		goto err_callback;
>> +	names = kmalloc_array(nvqs, sizeof(*names), GFP_KERNEL);
>> +	if (!names)
>> +		goto err_names;
>> +
>> +	callbacks[0] = balloon_ack;
>> +	names[0] = "inflate";
>> +	callbacks[1] = balloon_ack;
>> +	names[1] = "deflate";
>> +
>> +	i = 2;
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>> +		callbacks[i] = stats_request;
>> +		names[i] = "stats";
>> +		i++;
>> +	}
>>   
>> -	/*
>> -	 * We expect two virtqueues: inflate and deflate, and
>> -	 * optionally stat.
>> -	 */
>> -	nvqs = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) ? 3 : 2;
>> -	err = virtio_find_vqs(vb->vdev, nvqs, vqs, callbacks, names, NULL);
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ)) {
>> +		callbacks[i] = NULL;
>> +		names[i] = "free_page_vq";
>> +	}
>> +
>> +	err = vb->vdev->config->find_vqs(vb->vdev, nvqs, vqs, callbacks, names,
>> +					 NULL, NULL);
>>   	if (err)
>> -		return err;
>> +		goto err_find;
>>   
>>   	vb->inflate_vq = vqs[0];
>>   	vb->deflate_vq = vqs[1];
>> +	i = 2;
>>   	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>> -		struct scatterlist sg;
>> -		unsigned int num_stats;
>> -		vb->stats_vq = vqs[2];
>> -
>> +		vb->stats_vq = vqs[i++];
>>   		/*
>>   		 * Prime this virtqueue with one buffer so the hypervisor can
>>   		 * use it to signal us later (it can't be broken yet!).
>>   		 */
>> -		num_stats = update_balloon_stats(vb);
>> -
>> -		sg_init_one(&sg, vb->stats, sizeof(vb->stats[0]) * num_stats);
>> +		sg_init_one(&sg, vb->stats, sizeof(vb->stats));
>>   		if (virtqueue_add_outbuf(vb->stats_vq, &sg, 1, vb, GFP_KERNEL)
>> -		    < 0)
>> -			BUG();
>> +		    < 0) {
>> +			dev_warn(&vb->vdev->dev, "%s: add stat_vq failed\n",
>> +				 __func__);
>> +			goto err_find;
>> +		}
>>   		virtqueue_kick(vb->stats_vq);
>>   	}
>> +
>> +	if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_VQ))
>> +		vb->free_page_vq = vqs[i];
>> +
>> +	kfree(names);
>> +	kfree(callbacks);
>> +	kfree(vqs);
>>   	return 0;
>   
> We can assign err=0 and remove above duplicate code?
>   

Where do you want to assign err=0? Could you show it using code?


Best,
Wei

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