From: "Michael S. Tsirkin" <mst@redhat.com>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
nitesh@redhat.com, kvm@vger.kernel.org, david@redhat.com,
dave.hansen@intel.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, akpm@linux-foundation.org,
yang.zhang.wz@gmail.com, pagupta@redhat.com, riel@surriel.com,
konrad.wilk@oracle.com, lcapitulino@redhat.com,
wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com,
dan.j.williams@intel.com
Subject: Re: [PATCH v2 5/5] virtio-balloon: Add support for providing page hints to host
Date: Wed, 24 Jul 2019 16:43:39 -0400 [thread overview]
Message-ID: <20190724164255-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <e11ba530cda97d3cc8efaeb105290cfe32db6cba.camel@linux.intel.com>
On Wed, Jul 24, 2019 at 01:37:47PM -0700, Alexander Duyck wrote:
> On Wed, 2019-07-24 at 15:02 -0400, Michael S. Tsirkin wrote:
> > On Wed, Jul 24, 2019 at 10:05:14AM -0700, Alexander Duyck wrote:
> > > From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> > >
> > > Add support for the page hinting feature provided by virtio-balloon.
> > > Hinting 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.
> > >
> > > Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> >
> > Looking at the design, it seems that hinted pages can immediately be
> > reused. I wonder how we can efficiently support this
> > with kvm when poisoning is in effect. Of course we can just
> > ignore the poison. However it seems cleaner to
> > 1. verify page is poisoned with the correct value
> > 2. fill the page with the correct value on fault
> >
> > Requirement 2 requires some kind of madvise that
> > will save the poison e.g. in the VMA.
> >
> > Not a blocker for sure ...
>
> As per our discussion in the other patch I agree that we should either
> ignore the hint/report if page poisoning is enabled, or page poisoning
> should result in us poisoning the page when it is faulted back in. I had
> assumed we were doing the latter, I didn't realize that is was just
> disabling the free page hinting.
In fact I see that the latest versions of qemu don't seem to do
the later either. Need to fix that ASAP...
> > > ---
> > > drivers/virtio/Kconfig | 1 +
> > > drivers/virtio/virtio_balloon.c | 47 +++++++++++++++++++++++++++++++++++
> > > include/uapi/linux/virtio_balloon.h | 1 +
> > > 3 files changed, 49 insertions(+)
> > >
> > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> > > index 078615cf2afc..d45556ae1f81 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_HINTING
> > > ---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 226fbb995fb0..dee9f8f3ad09 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_hinting.h>
> > >
> > > /*
> > > * Balloon device works in 4K page units. So each page is pointed to by
> > > @@ -27,6 +28,7 @@
> > > */
> > > #define VIRTIO_BALLOON_PAGES_PER_PAGE (unsigned)(PAGE_SIZE >> VIRTIO_BALLOON_PFN_SHIFT)
> > > #define VIRTIO_BALLOON_ARRAY_PFNS_MAX 256
> > > +#define VIRTIO_BALLOON_ARRAY_HINTS_MAX 32
> > > #define VIRTBALLOON_OOM_NOTIFY_PRIORITY 80
> > >
> > > #define VIRTIO_BALLOON_FREE_PAGE_ALLOC_FLAG (__GFP_NORETRY | __GFP_NOWARN | \
> > > @@ -46,6 +48,7 @@ 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
> > > };
> > >
> > > @@ -113,6 +116,10 @@ struct virtio_balloon {
> > >
> > > /* To register a shrinker to shrink memory upon memory pressure */
> > > struct shrinker shrinker;
> > > +
> > > + /* Unused page hinting device */
> > > + struct virtqueue *hinting_vq;
> > > + struct page_hinting_dev_info ph_dev_info;
> > > };
> > >
> > > static struct virtio_device_id id_table[] = {
> > > @@ -152,6 +159,22 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
> > >
> > > }
> > >
> > > +void virtballoon_page_hinting_react(struct page_hinting_dev_info *ph_dev_info,
> > > + unsigned int num_hints)
> > > +{
> > > + struct virtio_balloon *vb =
> > > + container_of(ph_dev_info, struct virtio_balloon, ph_dev_info);
> > > + struct virtqueue *vq = vb->hinting_vq;
> > > + unsigned int unused;
> > > +
> > > + /* We should always be able to add these buffers to an empty queue. */
> >
> > can be an out of memory condition, and then ...
> >
> > > + virtqueue_add_inbuf(vq, ph_dev_info->sg, num_hints, vb, GFP_KERNEL);
> > > + virtqueue_kick(vq);
> >
> > ... this will block forever.
> >
> > > + /* When host has read buffer, this completes via balloon_ack */
> > > + wait_event(vb->acked, virtqueue_get_buf(vq, &unused));
> >
> > However below I suggest limiting capacity which will solve
> > this problem for you.
>
> I wasn't aware that virtqueue_add_inbuf actually performed an allocation.
>
> > > +}
> > > +
> > > static void set_page_pfns(struct virtio_balloon *vb,
> > > __virtio32 pfns[], struct page *page)
> > > {
> > > @@ -476,6 +499,7 @@ 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";
> > > @@ -487,11 +511,19 @@ 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] = balloon_ack;
> > > + }
> > > +
> > > 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)) {
> > > @@ -924,12 +956,24 @@ static int virtballoon_probe(struct virtio_device *vdev)
> > > if (err)
> > > goto out_del_balloon_wq;
> > > }
> > > +
> > > + vb->ph_dev_info.react = virtballoon_page_hinting_react;
> > > + vb->ph_dev_info.capacity = VIRTIO_BALLOON_ARRAY_HINTS_MAX;
> >
> > As explained above I think you should limit this by vq size.
> > Otherwise virtqueue add buf might fail.
> > In fact by struct spec reading you need to limit it
> > anyway otherwise it will fail unconditionally.
> > In practice on most hypervisors it will typically work ...
>
> So I would just need to query that via the virtqueue_get_vring_size
> function correct? I could probably just set capacity to the minimum of the
> HINTS_MAX and that value right?
>
>
next prev parent reply other threads:[~2019-07-24 20:43 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-24 16:54 [PATCH v2 0/5] mm / virtio: Provide support for page hinting Alexander Duyck
2019-07-24 16:56 ` [PATCH v2 1/5] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-07-24 16:58 ` [PATCH v2 2/5] mm: Move set/get_pcppage_migratetype to mmzone.h Alexander Duyck
2019-07-24 17:00 ` [PATCH v2 3/5] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-07-24 17:03 ` [PATCH v2 4/5] mm: Introduce Hinted pages Alexander Duyck
2019-07-25 8:53 ` David Hildenbrand
2019-07-25 11:46 ` Nitesh Narayan Lal
2019-07-25 11:54 ` David Hildenbrand
2019-07-25 15:59 ` Alexander Duyck
2019-07-25 16:48 ` David Hildenbrand
2019-07-25 17:38 ` Alexander Duyck
2019-07-25 18:32 ` David Hildenbrand
2019-07-25 20:37 ` Alexander Duyck
2019-07-25 20:44 ` David Hildenbrand
2019-07-26 12:24 ` Nitesh Narayan Lal
2019-07-26 16:38 ` Alexander Duyck
2019-07-24 17:05 ` [PATCH v2 5/5] virtio-balloon: Add support for providing page hints to host Alexander Duyck
2019-07-24 19:02 ` Michael S. Tsirkin
2019-07-24 19:07 ` Nitesh Narayan Lal
2019-07-24 19:26 ` Michael S. Tsirkin
2019-07-24 20:37 ` Alexander Duyck
2019-07-24 20:43 ` Michael S. Tsirkin [this message]
2019-07-25 14:44 ` Nitesh Narayan Lal
2019-07-25 14:54 ` Michael S. Tsirkin
2019-07-25 14:56 ` Alexander Duyck
2019-07-25 14:59 ` Michael S. Tsirkin
2019-07-25 17:42 ` Nitesh Narayan Lal
2019-07-25 19:54 ` Alexander Duyck
2019-07-24 17:12 ` [PATCH v2 QEMU] virtio-balloon: Provide a interface for "bubble hinting" Alexander Duyck
2019-07-24 19:02 ` Michael S. Tsirkin
2019-07-24 20:18 ` Alexander Duyck
2019-07-24 20:29 ` Nitesh Narayan Lal
2019-07-24 20:42 ` Michael S. Tsirkin
2019-07-29 16:58 ` Alexander Duyck
2019-07-29 19:25 ` Michael S. Tsirkin
2019-07-29 20:21 ` Alexander Duyck
2019-07-29 20:49 ` Michael S. Tsirkin
2019-07-29 21:37 ` Alexander Duyck
2019-07-29 22:11 ` Michael S. Tsirkin
2019-07-24 20:46 ` Michael S. Tsirkin
2019-07-24 21:14 ` Alexander Duyck
2019-07-25 11:57 ` Nitesh Narayan Lal
2019-07-25 14:57 ` Alexander Duyck
2019-07-24 21:38 ` Michael S. Tsirkin
2019-07-24 22:03 ` Alexander Duyck
2019-07-24 22:08 ` Michael S. Tsirkin
2019-07-24 22:27 ` Alexander Duyck
2019-07-25 6:07 ` Michael S. Tsirkin
2019-07-25 11:35 ` Nitesh Narayan Lal
2019-07-25 15:05 ` Alexander Duyck
2019-07-25 15:16 ` Michael S. Tsirkin
2019-07-25 16:16 ` Alexander Duyck
2019-07-25 17:19 ` Michael S. Tsirkin
2019-07-25 18:25 ` Nitesh Narayan Lal
2019-07-25 20:00 ` Alexander Duyck
2019-07-25 20:14 ` Nitesh Narayan Lal
2019-07-24 18:40 ` [PATCH v2 0/5] mm / virtio: Provide support for page hinting Nitesh Narayan Lal
2019-07-24 18:41 ` David Hildenbrand
2019-07-24 19:31 ` Michael S. Tsirkin
2019-07-24 19:47 ` David Hildenbrand
2019-07-24 19:54 ` Nitesh Narayan Lal
2019-07-24 21:32 ` Michael S. Tsirkin
2019-07-24 19:24 ` Michael S. Tsirkin
2019-07-24 20:27 ` Alexander Duyck
2019-07-24 20:38 ` Nitesh Narayan Lal
2019-07-24 21:00 ` Alexander Duyck
2019-07-25 12:08 ` Nitesh Narayan Lal
2019-07-24 20:38 ` Michael S. Tsirkin
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