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

From: David Hildenbrand
Date: Tue Jun 04 2019 - 03:16:36 EST

On 04.06.19 00:38, 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.

+1

[...]
>
>> +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? 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.

+1

[...]

>
>> + 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.

+1

>
>> +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.

I think I prefer "addr + size".

>
> Same comment here. Make this array a part of virtio_balloon and you
> don't have to free it.
>
>> +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.

+1

>
>> +#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)) {

Nitesh, you should only disable if you actually enabled it
(page_hinting_flag).



--

Thanks,

David / dhildenb