Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-02-01 Thread Michael S. Tsirkin 
On Thu, Jan 25, 2018 at 08:28:52PM +0900, Tetsuo Handa wrote:
> On 2018/01/25 12:32, Wei Wang wrote:
> > On 01/25/2018 01:15 AM, Michael S. Tsirkin wrote:
> >> On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote:
> >> +
> >> +static void report_free_page_func(struct work_struct *work)
> >> +{
> >> +struct virtio_balloon *vb;
> >> +unsigned long flags;
> >> +
> >> +vb = container_of(work, struct virtio_balloon, report_free_page_work);
> >> +
> >> +/* Start by sending the obtained cmd id to the host with an outbuf */
> >> +send_cmd_id(vb, >start_cmd_id);
> >> +
> >> +/*
> >> + * Set start_cmd_id to VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID to
> >> + * indicate a new request can be queued.
> >> + */
> >> +spin_lock_irqsave(>stop_update_lock, flags);
> >> +vb->start_cmd_id = cpu_to_virtio32(vb->vdev,
> >> +VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID);
> >> +spin_unlock_irqrestore(>stop_update_lock, flags);
> >> +
> >> +walk_free_mem_block(vb, 0, _balloon_send_free_pages);
> >> Can you teach walk_free_mem_block to return the && of all
> >> return calls, so caller knows whether it completed?
> > 
> > There will be two cases that can cause walk_free_mem_block to return 
> > without completing:
> > 1) host requests to stop in advance
> > 2) vq->broken
> > 
> > How about letting walk_free_mem_block simply return the value returned by 
> > its callback (i.e. virtio_balloon_send_free_pages)?
> > 
> > For host requests to stop, it returns "1", and the above only bails out 
> > when walk_free_mem_block return a "< 0" value.
> 
> I feel that virtio_balloon_send_free_pages is doing too heavy things.
> 
> It can be called for many times with IRQ disabled. Number of times
> it is called depends on amount of free pages (and fragmentation state).
> Generally, more free pages, more calls.
> 
> Then, why don't you allocate some pages for holding all pfn values
> and then call walk_free_mem_block() only for storing pfn values
> and then send pfn values without disabling IRQ?

So going over it, at some level we are talking about optimizations here.

I'll go over it one last time but at some level we might
be able to make progress faster if we start by enabling
the functionality in question.
If there are no other issues, I'm inclined to merge.

If nothing else, this
will make it possible for people to experiment and
report sources of overhead.

-- 
MST
___
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-01-25 Thread Wei Wang 

On 01/25/2018 07:28 PM, Tetsuo Handa wrote:

On 2018/01/25 12:32, Wei Wang wrote:

On 01/25/2018 01:15 AM, Michael S. Tsirkin wrote:

On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote:
+
+static void report_free_page_func(struct work_struct *work)
+{
+struct virtio_balloon *vb;
+unsigned long flags;
+
+vb = container_of(work, struct virtio_balloon, report_free_page_work);
+
+/* Start by sending the obtained cmd id to the host with an outbuf */
+send_cmd_id(vb, >start_cmd_id);
+
+/*
+ * Set start_cmd_id to VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID to
+ * indicate a new request can be queued.
+ */
+spin_lock_irqsave(>stop_update_lock, flags);
+vb->start_cmd_id = cpu_to_virtio32(vb->vdev,
+VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID);
+spin_unlock_irqrestore(>stop_update_lock, flags);
+
+walk_free_mem_block(vb, 0, _balloon_send_free_pages);
Can you teach walk_free_mem_block to return the && of all
return calls, so caller knows whether it completed?

There will be two cases that can cause walk_free_mem_block to return without 
completing:
1) host requests to stop in advance
2) vq->broken

How about letting walk_free_mem_block simply return the value returned by its 
callback (i.e. virtio_balloon_send_free_pages)?

For host requests to stop, it returns "1", and the above only bails out when 
walk_free_mem_block return a "< 0" value.

I feel that virtio_balloon_send_free_pages is doing too heavy things.

It can be called for many times with IRQ disabled. Number of times
it is called depends on amount of free pages (and fragmentation state).
Generally, more free pages, more calls.

Then, why don't you allocate some pages for holding all pfn values
and then call walk_free_mem_block() only for storing pfn values
and then send pfn values without disabling IRQ?


We have actually tried many methods for this feature before, and what 
you suggested is one of them, and you could also find the related 
discussion in earlier versions. In addition to the complexity of that 
method (if thinking deeper along that line), I can share the performance 
(the live migration time) comparison of that method with this one in 
this patch: ~405ms vs. ~260 ms.


The things that you worried about have also been discussed actually. The 
strategy is that we start with something fundamental and increase 
incrementally (if you check earlier versions, we also have a method 
which makes the lock finer granularity, but we decided to leave this to 
the future improvement for prudence purpose). If possible, please let 
Michael review this patch, he already knows all those things. We will 
finish this feature as soon as possible, and then discuss with you about 
another one if you want. Thanks.


Best,
Wei



___
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-01-25 Thread Tetsuo Handa 
On 2018/01/25 12:32, Wei Wang wrote:
> On 01/25/2018 01:15 AM, Michael S. Tsirkin wrote:
>> On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote:
>> +
>> +static void report_free_page_func(struct work_struct *work)
>> +{
>> +struct virtio_balloon *vb;
>> +unsigned long flags;
>> +
>> +vb = container_of(work, struct virtio_balloon, report_free_page_work);
>> +
>> +/* Start by sending the obtained cmd id to the host with an outbuf */
>> +send_cmd_id(vb, >start_cmd_id);
>> +
>> +/*
>> + * Set start_cmd_id to VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID to
>> + * indicate a new request can be queued.
>> + */
>> +spin_lock_irqsave(>stop_update_lock, flags);
>> +vb->start_cmd_id = cpu_to_virtio32(vb->vdev,
>> +VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID);
>> +spin_unlock_irqrestore(>stop_update_lock, flags);
>> +
>> +walk_free_mem_block(vb, 0, _balloon_send_free_pages);
>> Can you teach walk_free_mem_block to return the && of all
>> return calls, so caller knows whether it completed?
> 
> There will be two cases that can cause walk_free_mem_block to return without 
> completing:
> 1) host requests to stop in advance
> 2) vq->broken
> 
> How about letting walk_free_mem_block simply return the value returned by its 
> callback (i.e. virtio_balloon_send_free_pages)?
> 
> For host requests to stop, it returns "1", and the above only bails out when 
> walk_free_mem_block return a "< 0" value.

I feel that virtio_balloon_send_free_pages is doing too heavy things.

It can be called for many times with IRQ disabled. Number of times
it is called depends on amount of free pages (and fragmentation state).
Generally, more free pages, more calls.

Then, why don't you allocate some pages for holding all pfn values
and then call walk_free_mem_block() only for storing pfn values
and then send pfn values without disabling IRQ?
___
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-01-25 Thread Wei Wang 

On 01/25/2018 01:15 AM, Michael S. Tsirkin wrote:

On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote:
  


What is this doing? Basically handling the case where vq is broken?
It's kind of ugly to tweak feature bits, most code assumes they never
change.  Please just return an error to caller instead and handle it
there.

You can then avoid sprinking the check for the feature bit
all over the code.



One thing I don't like about this one is that the previous request
will still try to run to completion.

And it all seems pretty complex.

How about:
- pass cmd id to a queued work
- queued work gets that cmd id, stores a copy and uses that,
   re-checking periodically - stop if cmd id changes:
   will replace  report_free_page too since that's set to
   stop.

This means you do not reuse the queued cmd id also
for the buffer - which is probably for the best.


Thanks for the suggestion. Please have a check how it's implemented in v25.
Just a little reminder that work queue has internally ensured that there 
is no re-entrant of the same queued function.


Best,
Wei
___
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-01-24 Thread Wei Wang 

On 01/25/2018 01:15 AM, Michael S. Tsirkin wrote:

On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote:
+
+static void report_free_page_func(struct work_struct *work)
+{
+   struct virtio_balloon *vb;
+   unsigned long flags;
+
+   vb = container_of(work, struct virtio_balloon, report_free_page_work);
+
+   /* Start by sending the obtained cmd id to the host with an outbuf */
+   send_cmd_id(vb, >start_cmd_id);
+
+   /*
+* Set start_cmd_id to VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID to
+* indicate a new request can be queued.
+*/
+   spin_lock_irqsave(>stop_update_lock, flags);
+   vb->start_cmd_id = cpu_to_virtio32(vb->vdev,
+   VIRTIO_BALLOON_FREE_PAGE_REPORT_STOP_ID);
+   spin_unlock_irqrestore(>stop_update_lock, flags);
+
+   walk_free_mem_block(vb, 0, _balloon_send_free_pages);
Can you teach walk_free_mem_block to return the && of all
return calls, so caller knows whether it completed?


There will be two cases that can cause walk_free_mem_block to return 
without completing:

1) host requests to stop in advance
2) vq->broken

How about letting walk_free_mem_block simply return the value returned 
by its callback (i.e. virtio_balloon_send_free_pages)?


For host requests to stop, it returns "1", and the above only bails out 
when walk_free_mem_block return a "< 0" value.


Best,
Wei
___
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH v24 2/2] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

2018-01-24 Thread Michael S. Tsirkin 
On Wed, Jan 24, 2018 at 06:42:42PM +0800, Wei Wang wrote:
> Negotiation of the VIRTIO_BALLOON_F_FREE_PAGE_HINT 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 
> Signed-off-by: Liang Li 
> Cc: Michael S. Tsirkin 
> Cc: Michal Hocko 
> ---
>  drivers/virtio/virtio_balloon.c | 265 
> +++-
>  include/uapi/linux/virtio_balloon.h |   7 +
>  2 files changed, 236 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index a1fb52c..4440873 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -51,9 +51,21 @@ MODULE_PARM_DESC(oom_pages, "pages to free on OOM");
>  static struct vfsmount *balloon_mnt;
>  #endif
>  
> +/* The number of virtqueues supported by virtio-balloon */
> +#define VIRTIO_BALLOON_VQ_NUM4
> +#define VIRTIO_BALLOON_VQ_ID_INFLATE 0
> +#define VIRTIO_BALLOON_VQ_ID_DEFLATE 1
> +#define VIRTIO_BALLOON_VQ_ID_STATS   2
> +#define VIRTIO_BALLOON_VQ_ID_FREE_PAGE   3
> +

Please do an enum instead of defines. VQ_ID can be just VQ
(it's not an ID, it's just the number).


>  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 +75,13 @@ 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 */
> + __virtio32 start_cmd_id;
> + /* Stores STOP_ID as a sign to tell host that the reporting is done */
> + __virtio32 stop_cmd_id;
> +
>   /* Waiting for host to ack the pages we released. */
>   wait_queue_head_t acked;
>  
> @@ -281,6 +300,53 @@ static unsigned int update_balloon_stats(struct 
> virtio_balloon *vb)
>   return idx;
>  }
>  
> +static int add_one_sg(struct virtqueue *vq, unsigned long pfn, uint32_t len)
> +{
> + struct scatterlist sg;
> + unsigned int unused;
> + int ret = 0;
> +
> + sg_init_table(, 1);
> + sg_set_page(, pfn_to_page(pfn), len, 0);
> +
> + /* Detach all the used buffers from the vq */
> + while (virtqueue_get_buf(vq, ))
> + ;
> +
> + /*
> +  * Since this is an optimization feature, losing a couple of free
> +  * pages to report isn't important. We simply return 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.
> +  * There is always one entry reserved for the cmd id to use.
> +  */
> + if (vq->num_free > 1)
> + ret = virtqueue_add_inbuf(vq, , 1, vq, GFP_KERNEL);
> +
> + if (vq->num_free < virtqueue_get_vring_size(vq) / 2)
> + virtqueue_kick(vq);
> +
> + return ret;
> +}
> +
> +static void send_cmd_id(struct virtio_balloon *vb, __virtio32 *cmd_id)
> +{
> + struct scatterlist sg;
> + struct virtqueue *vq = vb->free_page_vq;
> +
> + if (unlikely(!virtio_has_feature(vb->vdev,
> +  VIRTIO_BALLOON_F_FREE_PAGE_HINT)))
> + return;
> +
> + sg_init_one(, cmd_id, sizeof(*cmd_id));
> +
> + if (virtqueue_add_outbuf(vq, , 1, vb, GFP_KERNEL))
> + __virtio_clear_bit(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT);

What is this doing? Basically handling the case where vq is broken?
It's kind of ugly to tweak feature bits, most code assumes they never
change.  Please just return an error to caller instead and handle it
there.

You can then avoid sprinking the check for the feature bit
all over the code.

> +
> + virtqueue_kick(vq);
> +}
> +
>  /*
>   * While most virtqueues communicate