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Message-ID: <b8cbf72d-55a7-4a58-6d08-b0ac5fa86e82@redhat.com>
Date: Tue, 11 Feb 2020 12:03:57 +0100
From: David Hildenbrand <david@...hat.com>
To: Alexander Duyck <alexander.duyck@...il.com>, kvm@...r.kernel.org,
mst@...hat.com, linux-kernel@...r.kernel.org, willy@...radead.org,
mhocko@...nel.org, linux-mm@...ck.org, akpm@...ux-foundation.org,
mgorman@...hsingularity.net, vbabka@...e.cz
Cc: yang.zhang.wz@...il.com, nitesh@...hat.com, konrad.wilk@...cle.com,
pagupta@...hat.com, riel@...riel.com, lcapitulino@...hat.com,
dave.hansen@...el.com, wei.w.wang@...el.com, aarcange@...hat.com,
pbonzini@...hat.com, dan.j.williams@...el.com,
alexander.h.duyck@...ux.intel.com, osalvador@...e.de
Subject: Re: [PATCH v16.1 6/9] virtio-balloon: Add support for providing free
page reports to host
On 22.01.20 18:43, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
>
> Add support for the page reporting feature provided by virtio-balloon.
> Reporting differs from the regular balloon functionality in that is is
> much less durable than a standard memory balloon. Instead of creating a
> list of pages that cannot be accessed the pages are only inaccessible
> while they are being indicated to the virtio interface. Once the
> interface has acknowledged them they are placed back into their respective
> free lists and are once again accessible by the guest system.
>
> Unlike a standard balloon we don't inflate and deflate the pages. Instead
> we perform the reporting, and once the reporting is completed it is
> assumed that the page has been dropped from the guest and will be faulted
> back in the next time the page is accessed.
>
> Acked-by: Michael S. Tsirkin <mst@...hat.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> ---
> drivers/virtio/Kconfig | 1 +
> drivers/virtio/virtio_balloon.c | 64 +++++++++++++++++++++++++++++++++++
> include/uapi/linux/virtio_balloon.h | 1 +
> 3 files changed, 66 insertions(+)
>
> diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> index 078615cf2afc..4b2dd8259ff5 100644
> --- a/drivers/virtio/Kconfig
> +++ b/drivers/virtio/Kconfig
> @@ -58,6 +58,7 @@ config VIRTIO_BALLOON
> tristate "Virtio balloon driver"
> depends on VIRTIO
> select MEMORY_BALLOON
> + select PAGE_REPORTING
> ---help---
> This driver supports increasing and decreasing the amount
> of memory within a KVM guest.
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 40bb7693e3de..a07b9e18a292 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -19,6 +19,7 @@
> #include <linux/mount.h>
> #include <linux/magic.h>
> #include <linux/pseudo_fs.h>
> +#include <linux/page_reporting.h>
>
> /*
> * Balloon device works in 4K page units. So each page is pointed to by
> @@ -47,6 +48,7 @@ enum virtio_balloon_vq {
> VIRTIO_BALLOON_VQ_DEFLATE,
> VIRTIO_BALLOON_VQ_STATS,
> VIRTIO_BALLOON_VQ_FREE_PAGE,
> + VIRTIO_BALLOON_VQ_REPORTING,
> VIRTIO_BALLOON_VQ_MAX
> };
>
> @@ -114,6 +116,10 @@ struct virtio_balloon {
>
> /* To register a shrinker to shrink memory upon memory pressure */
> struct shrinker shrinker;
> +
> + /* Free page reporting device */
> + struct virtqueue *reporting_vq;
> + struct page_reporting_dev_info pr_dev_info;
> };
>
> static struct virtio_device_id id_table[] = {
> @@ -153,6 +159,33 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
>
> }
>
> +int virtballoon_free_page_report(struct page_reporting_dev_info *pr_dev_info,
> + struct scatterlist *sg, unsigned int nents)
> +{
> + struct virtio_balloon *vb =
> + container_of(pr_dev_info, struct virtio_balloon, pr_dev_info);
> + struct virtqueue *vq = vb->reporting_vq;
> + unsigned int unused, err;
> +
> + /* We should always be able to add these buffers to an empty queue. */
> + err = virtqueue_add_inbuf(vq, sg, nents, vb, GFP_NOWAIT | __GFP_NOWARN);
> +
> + /*
> + * In the extremely unlikely case that something has occurred and we
> + * are able to trigger an error we will simply display a warning
> + * and exit without actually processing the pages.
> + */
> + if (WARN_ON_ONCE(err))
> + return err;
> +
> + virtqueue_kick(vq);
> +
> + /* When host has read buffer, this completes via balloon_ack */
> + wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
> +
> + return 0;
> +}
Did you see the discussion regarding unifying handling of
inflate/deflate/free_page_hinting_free_page_reporting, requested by
Michael? I think free page reporting is special and shall be left alone.
VIRTIO_BALLOON_F_REPORTING is nothing but a more advanced inflate, right
(sg, inflate based on size - not "virtio pages")? And you rely on
deflates not being required before reusing an inflated page.
I suggest the following:
/* New interface (+ 2 virtqueues) to inflate/deflate using a SG */
VIRTIO_BALLOON_F_SG
/*
* No need to deflate when reusing pages (once the inflate request was
* processed). Applies to all inflate queues.
*/
VIRTIO_BALLOON_F_OPTIONAL_DEFLATE
And two new virtqueues
VIRTIO_BALLOON_VQ_INFLATE_SG
VIRTIO_BALLOON_VQ_DEFLATE_SG
Your feature would depend on VIRTIO_BALLOON_F_SG &&
VIRTIO_BALLOON_F_OPTIONAL_DEFLATE. VIRTIO_BALLOON_F_OPTIONAL_DEFLATE
could be reused to avoid deflating on certain events (e.g., from
OOM/shrinker).
Thoughts?
--
Thanks,
David / dhildenb
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