Re: [RFC][Patch v10 2/2] virtio-balloon: page_hinting: reporting to the host

[Nitesh Narayan Lal]

On 6/3/19 6:38 PM, Alexander Duyck wrote:
> On Mon, Jun 3, 2019 at 10:04 AM Nitesh Narayan Lal <nitesh@xxxxxxxxxx> wrote:
>> Enables the kernel to negotiate VIRTIO_BALLOON_F_HINTING feature with the
>> host. If it is available and page_hinting_flag is set to true, page_hinting
>> is enabled and its callbacks are configured along with the max_pages count
>> which indicates the maximum number of pages that can be isolated and hinted
>> at a time. Currently, only free pages of order >= (MAX_ORDER - 2) are
>> reported. To prevent any false OOM max_pages count is set to 16.
>>
>> By default page_hinting feature is enabled and gets loaded as soon
>> as the virtio-balloon driver is loaded. However, it could be disabled
>> by writing the page_hinting_flag which is a virtio-balloon parameter.
>>
>> Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
>> ---
>>  drivers/virtio/virtio_balloon.c     | 112 +++++++++++++++++++++++++++-
>>  include/uapi/linux/virtio_balloon.h |  14 ++++
>>  2 files changed, 125 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
>> index f19061b585a4..40f09ea31643 100644
>> --- a/drivers/virtio/virtio_balloon.c
>> +++ b/drivers/virtio/virtio_balloon.c
>> @@ -31,6 +31,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/mount.h>
>>  #include <linux/magic.h>
>> +#include <linux/page_hinting.h>
>>
>>  /*
>>   * Balloon device works in 4K page units.  So each page is pointed to by
>> @@ -48,6 +49,7 @@
>>  /* The size of a free page block in bytes */
>>  #define VIRTIO_BALLOON_FREE_PAGE_SIZE \
>>         (1 << (VIRTIO_BALLOON_FREE_PAGE_ORDER + PAGE_SHIFT))
>> +#define VIRTIO_BALLOON_PAGE_HINTING_MAX_PAGES  16
>>
>>  #ifdef CONFIG_BALLOON_COMPACTION
>>  static struct vfsmount *balloon_mnt;
>> @@ -58,6 +60,7 @@ enum virtio_balloon_vq {
>>         VIRTIO_BALLOON_VQ_DEFLATE,
>>         VIRTIO_BALLOON_VQ_STATS,
>>         VIRTIO_BALLOON_VQ_FREE_PAGE,
>> +       VIRTIO_BALLOON_VQ_HINTING,
>>         VIRTIO_BALLOON_VQ_MAX
>>  };
>>
>> @@ -67,7 +70,8 @@ enum virtio_balloon_config_read {
>>
>>  struct virtio_balloon {
>>         struct virtio_device *vdev;
>> -       struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq;
>> +       struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq,
>> +                        *hinting_vq;
>>
>>         /* Balloon's own wq for cpu-intensive work items */
>>         struct workqueue_struct *balloon_wq;
>> @@ -125,6 +129,9 @@ struct virtio_balloon {
>>
>>         /* To register a shrinker to shrink memory upon memory pressure */
>>         struct shrinker shrinker;
>> +
>> +       /* object pointing at the array of isolated pages ready for hinting */
>> +       struct hinting_data *hinting_arr;
> Just make this an array of size VIRTIO_BALLOON_PAGE_HINTING_MAX_PAGES.
> It will save a bunch of complexity later.
Make sense.
>>  };
>>
>>  static struct virtio_device_id id_table[] = {
>> @@ -132,6 +139,85 @@ static struct virtio_device_id id_table[] = {
>>         { 0 },
>>  };
>>
>> +#ifdef CONFIG_PAGE_HINTING
> Instead of having CONFIG_PAGE_HINTING enable this, maybe we should
> have virtio-balloon enable CONFIG_PAGE_HINTING.
>
>> +struct virtio_balloon *hvb;
>> +bool page_hinting_flag = true;
>> +module_param(page_hinting_flag, bool, 0444);
>> +MODULE_PARM_DESC(page_hinting_flag, "Enable page hinting");
>> +
>> +static bool virtqueue_kick_sync(struct virtqueue *vq)
>> +{
>> +       u32 len;
>> +
>> +       if (likely(virtqueue_kick(vq))) {
>> +               while (!virtqueue_get_buf(vq, &len) &&
>> +                      !virtqueue_is_broken(vq))
>> +                       cpu_relax();
>> +               return true;
> Is this a synchronous setup? 
Yes.
> It seems kind of wasteful to have a
> thread busy waiting here like this. It might make more sense to just
> make this work like the other balloon queues and have a wait event
> with a wake up in the interrupt handler for the queue.

I can do that. I may have to use a flag or something else to
page_hinting.c as well to ensure that no
other bitmap scanning is initiated until then.

>
>> +       }
>> +       return false;
>> +}
>> +
>> +static void page_hinting_report(int entries)
>> +{
>> +       struct scatterlist sg;
>> +       struct virtqueue *vq = hvb->hinting_vq;
>> +       int err = 0;
>> +       struct hinting_data *hint_req;
>> +       u64 gpaddr;
>> +
>> +       hint_req = kmalloc(sizeof(*hint_req), GFP_KERNEL);
>> +       if (!hint_req)
>> +               return;
> Why do we need another allocation here? Couldn't you just allocate
> hint_req on the stack and then use that? I think we might be doing too
> much here. All this really needs to look like is something along the
> lines of tell_host() minus the wait_event.
>
>> +       gpaddr = virt_to_phys(hvb->hinting_arr);
>> +       hint_req->phys_addr = cpu_to_virtio64(hvb->vdev, gpaddr);
>> +       hint_req->size = cpu_to_virtio32(hvb->vdev, entries);
>> +       sg_init_one(&sg, hint_req, sizeof(*hint_req));
>> +       err = virtqueue_add_outbuf(vq, &sg, 1, hint_req, GFP_KERNEL);
>> +       if (!err)
>> +               virtqueue_kick_sync(hvb->hinting_vq);
>> +
>> +       kfree(hint_req);
>> +}
>> +
>> +int page_hinting_prepare(void)
>> +{
>> +       hvb->hinting_arr = kmalloc_array(VIRTIO_BALLOON_PAGE_HINTING_MAX_PAGES,
>> +                                        sizeof(*hvb->hinting_arr), GFP_KERNEL);
>> +       if (!hvb->hinting_arr)
>> +               return -ENOMEM;
>> +       return 0;
>> +}
>> +
> Why make the hinting_arr a dynamic allocation? You should probably
> just make it a static array within the virtio_balloon structure. Then
> you don't have the risk of an allocation failing and messing up the
> hints.
I agree.
>> +void hint_pages(struct list_head *pages)
>> +{
>> +       struct page *page, *next;
>> +       unsigned long pfn;
>> +       int idx = 0, order;
>> +
>> +       list_for_each_entry_safe(page, next, pages, lru) {
>> +               pfn = page_to_pfn(page);
>> +               order = page_private(page);
>> +               hvb->hinting_arr[idx].phys_addr = pfn << PAGE_SHIFT;
>> +               hvb->hinting_arr[idx].size = (1 << order) * PAGE_SIZE;
>> +               idx++;
>> +       }
>> +       page_hinting_report(idx);
>> +}
>> +
> Getting back to my suggestion from earlier today. It might make sense
> to not bother with the PAGE_SHIFT or PAGE_SIZE multiplication if you
> just record everything in VIRTIO_BALLOON_PAGES intead of using the
> actual address and size.
>
>> +void page_hinting_cleanup(void)
>> +{
>> +       kfree(hvb->hinting_arr);
>> +}
>> +
> Same comment here. Make this array a part of virtio_balloon and you
> don't have to free it.
+1
>
>> +static const struct page_hinting_cb hcb = {
>> +       .prepare = page_hinting_prepare,
>> +       .hint_pages = hint_pages,
>> +       .cleanup = page_hinting_cleanup,
>> +       .max_pages = VIRTIO_BALLOON_PAGE_HINTING_MAX_PAGES,
>> +};
> With the above changes prepare and cleanup can be dropped.
>
>> +#endif
>> +
>>  static u32 page_to_balloon_pfn(struct page *page)
>>  {
>>         unsigned long pfn = page_to_pfn(page);
>> @@ -488,6 +574,7 @@ static int init_vqs(struct virtio_balloon *vb)
>>         names[VIRTIO_BALLOON_VQ_DEFLATE] = "deflate";
>>         names[VIRTIO_BALLOON_VQ_STATS] = NULL;
>>         names[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
>> +       names[VIRTIO_BALLOON_VQ_HINTING] = NULL;
>>
>>         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>>                 names[VIRTIO_BALLOON_VQ_STATS] = "stats";
>> @@ -499,11 +586,18 @@ static int init_vqs(struct virtio_balloon *vb)
>>                 callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = NULL;
>>         }
>>
>> +       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) {
>> +               names[VIRTIO_BALLOON_VQ_HINTING] = "hinting_vq";
>> +               callbacks[VIRTIO_BALLOON_VQ_HINTING] = NULL;
>> +       }
>>         err = vb->vdev->config->find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX,
>>                                          vqs, callbacks, names, NULL, NULL);
>>         if (err)
>>                 return err;
>>
>> +       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING))
>> +               vb->hinting_vq = vqs[VIRTIO_BALLOON_VQ_HINTING];
>> +
>>         vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
>>         vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
>>         if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>> @@ -942,6 +1036,14 @@ static int virtballoon_probe(struct virtio_device *vdev)
>>                 if (err)
>>                         goto out_del_balloon_wq;
>>         }
>> +
>> +#ifdef CONFIG_PAGE_HINTING
>> +       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING) &&
>> +           page_hinting_flag) {
>> +               hvb = vb;
>> +               page_hinting_enable(&hcb);
>> +       }
>> +#endif
>>         virtio_device_ready(vdev);
>>
>>         if (towards_target(vb))
>> @@ -989,6 +1091,12 @@ static void virtballoon_remove(struct virtio_device *vdev)
>>                 destroy_workqueue(vb->balloon_wq);
>>         }
>>
>> +#ifdef CONFIG_PAGE_HINTING
>> +       if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) {
>> +               hvb = NULL;
>> +               page_hinting_disable();
>> +       }
>> +#endif
>>         remove_common(vb);
>>  #ifdef CONFIG_BALLOON_COMPACTION
>>         if (vb->vb_dev_info.inode)
>> @@ -1043,8 +1151,10 @@ static unsigned int features[] = {
>>         VIRTIO_BALLOON_F_MUST_TELL_HOST,
>>         VIRTIO_BALLOON_F_STATS_VQ,
>>         VIRTIO_BALLOON_F_DEFLATE_ON_OOM,
>> +       VIRTIO_BALLOON_F_HINTING,
>>         VIRTIO_BALLOON_F_FREE_PAGE_HINT,
>>         VIRTIO_BALLOON_F_PAGE_POISON,
>> +       VIRTIO_BALLOON_F_HINTING,
>>  };
>>
>>  static struct virtio_driver virtio_balloon_driver = {
>> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h
>> index a1966cd7b677..25e4f817c660 100644
>> --- a/include/uapi/linux/virtio_balloon.h
>> +++ b/include/uapi/linux/virtio_balloon.h
>> @@ -29,6 +29,7 @@
>>  #include <linux/virtio_types.h>
>>  #include <linux/virtio_ids.h>
>>  #include <linux/virtio_config.h>
>> +#include <linux/page_hinting.h>
>>
>>  /* The feature bitmap for virtio balloon */
>>  #define VIRTIO_BALLOON_F_MUST_TELL_HOST        0 /* Tell before reclaiming pages */
>> @@ -36,6 +37,7 @@
>>  #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM        2 /* Deflate balloon on OOM */
>>  #define VIRTIO_BALLOON_F_FREE_PAGE_HINT        3 /* VQ to report free pages */
>>  #define VIRTIO_BALLOON_F_PAGE_POISON   4 /* Guest is using page poisoning */
>> +#define VIRTIO_BALLOON_F_HINTING       5 /* Page hinting virtqueue */
>>
>>  /* Size of a PFN in the balloon interface. */
>>  #define VIRTIO_BALLOON_PFN_SHIFT 12
>> @@ -108,4 +110,16 @@ struct virtio_balloon_stat {
>>         __virtio64 val;
>>  } __attribute__((packed));
>>
>> +#ifdef CONFIG_PAGE_HINTING
>> +/*
>> + * struct hinting_data- holds the information associated with hinting.
>> + * @phys_add:  physical address associated with a page or the array holding
>> + *             the array of isolated pages.
>> + * @size:      total size associated with the phys_addr.
>> + */
>> +struct hinting_data {
>> +       __virtio64 phys_addr;
>> +       __virtio32 size;
>> +};
> So in order to avoid errors this should either have
> "__attribute__((packed))" added or it should be changed to a pair of
> u32 or u64 values so that it will always be the same size regardless
> of what platform it is built on.
I will take a look at this.
Thanks.
>> +#endif
>>  #endif /* _LINUX_VIRTIO_BALLOON_H */
>> --
>> 2.21.0
>>
-- 
Regards
Nitesh

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