From: "Michael S. Tsirkin" <mst@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
willy@infradead.org, mhocko@kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org, mgorman@techsingularity.net,
vbabka@suse.cz, yang.zhang.wz@gmail.com, nitesh@redhat.com,
konrad.wilk@oracle.com, pagupta@redhat.com, riel@surriel.com,
lcapitulino@redhat.com, dave.hansen@intel.com,
wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com,
dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com,
osalvador@suse.de
Subject: Re: [PATCH v16.1 6/9] virtio-balloon: Add support for providing free page reports to host
Date: Tue, 11 Feb 2020 06:47:44 -0500 [thread overview]
Message-ID: <20200211063441-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <b8cbf72d-55a7-4a58-6d08-b0ac5fa86e82@redhat.com>
On Tue, Feb 11, 2020 at 12:03:57PM +0100, David Hildenbrand wrote:
> On 22.01.20 18:43, Alexander Duyck wrote:
> > From: Alexander Duyck <alexander.h.duyck@linux.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@redhat.com>
> > Reviewed-by: David Hildenbrand <david@redhat.com>
> > Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.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.
Not sure what do you mean by "left alone here". Could you clarify?
> VIRTIO_BALLOON_F_REPORTING is nothing but a more advanced inflate, right
> (sg, inflate based on size - not "virtio pages")?
Not exactly - it's also initiated by guest as opposed to host, and
not guided by the ballon size request set by the host.
And uses a dedicated queue to avoid blocking other functionality ...
I really think this is more like an inflate immediately followed by deflate.
> 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?
I'd rather wait until we have a usecase and preferably a POC
showing it helps before we add optional deflate ...
For now I personally am fine with just making this go ahead as is,
and imply SG and OPTIONAL_DEFLATE just for this VQ.
Do you feel strongly we need to bring this up to a TC vote?
It means spec patch needs to be written, but it
does not have to be a big patch ...
> --
> Thanks,
>
> David / dhildenb
next prev parent reply other threads:[~2020-02-11 11:47 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 17:43 [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting Alexander Duyck
2020-01-22 17:43 ` [PATCH v16.1 1/9] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2020-01-22 17:43 ` [PATCH v16.1 2/9] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2020-01-22 17:43 ` [PATCH v16.1 3/9] mm: Add function __putback_isolated_page Alexander Duyck
2020-01-22 17:43 ` [PATCH v16.1 4/9] mm: Introduce Reported pages Alexander Duyck
2020-01-22 17:43 ` [PATCH v16.1 5/9] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2020-01-22 17:43 ` [PATCH v16.1 6/9] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
2020-02-11 11:03 ` David Hildenbrand
2020-02-11 11:47 ` Michael S. Tsirkin [this message]
2020-02-11 12:19 ` David Hildenbrand
2020-02-11 14:07 ` Michael S. Tsirkin
2020-02-11 14:31 ` David Hildenbrand
2020-02-11 14:48 ` Michael S. Tsirkin
2020-02-11 15:13 ` David Hildenbrand
2020-02-11 16:33 ` Alexander Duyck
2020-02-11 17:04 ` David Hildenbrand
2020-01-22 17:43 ` [PATCH v16.1 7/9] mm/page_reporting: Rotate reported pages to the tail of the list Alexander Duyck
2020-01-22 17:43 ` [PATCH v16.1 8/9] mm/page_reporting: Add budget limit on how many pages can be reported per pass Alexander Duyck
2020-01-22 17:44 ` [PATCH v16.1 9/9] mm/page_reporting: Add free page reporting documentation Alexander Duyck
2020-01-23 10:20 ` [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting Alexander Graf
2020-01-23 14:05 ` David Hildenbrand
2020-01-23 14:52 ` Alexander Graf
2020-01-24 13:25 ` David Hildenbrand
2020-01-24 16:20 ` David Hildenbrand
2020-01-23 16:26 ` Alexander Duyck
2020-01-23 16:54 ` Alexander Graf
2020-01-23 18:33 ` Alexander Duyck
2020-01-23 18:47 ` Graf (AWS), Alexander
2020-01-23 22:05 ` Alexander Duyck
2020-01-23 17:20 ` Dave Hansen
2020-01-23 19:23 ` Konrad Rzeszutek Wilk
2020-01-23 19:17 ` Johannes Weiner
2020-01-23 22:29 ` Alexander Duyck
2020-01-23 23:24 ` Dave Hansen
[not found] ` <20200124132352.12824-1-hdanton@sina.com>
2020-01-24 16:40 ` Alexander Graf
2020-02-03 22:05 ` Alexander Duyck
2020-02-10 19:18 ` Should I repost? (was: Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting) Alexander Duyck
2020-02-11 10:40 ` Mel Gorman
2020-02-11 22:57 ` Alexander Duyck
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