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Re: [PATCH v19 QEMU 3/4] virtio-balloon: Provide an interface for free p
From: |
Alexander Duyck |
Subject: |
Re: [PATCH v19 QEMU 3/4] virtio-balloon: Provide an interface for free page reporting |
Date: |
Wed, 15 Apr 2020 08:31:47 -0700 |
On Wed, Apr 15, 2020 at 1:17 AM David Hildenbrand <address@hidden> wrote:
>
> On 10.04.20 05:41, Alexander Duyck wrote:
> > From: Alexander Duyck <address@hidden>
> >
> > Add support for free page reporting. The idea is to function very similar
> > to how the balloon works in that we basically end up madvising the page as
> > not being used. However we don't really need to bother with any deflate
> > type logic since the page will be faulted back into the guest when it is
> > read or written to.
> >
> > This provides a new way of letting the guest proactively report free
> > pages to the hypervisor, so the hypervisor can reuse them. In contrast to
> > inflate/deflate that is triggered via the hypervisor explicitly.
>
> Much better, thanks!
>
> >
> > Signed-off-by: Alexander Duyck <address@hidden>
> > ---
> > hw/virtio/virtio-balloon.c | 63
> > +++++++++++++++++++++++++++++++++++-
> > include/hw/virtio/virtio-balloon.h | 2 +
> > 2 files changed, 62 insertions(+), 3 deletions(-)
> >
> > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> > index 1c6d36a29a04..86d8b48a8e3a 100644
> > --- a/hw/virtio/virtio-balloon.c
> > +++ b/hw/virtio/virtio-balloon.c
> > @@ -321,6 +321,57 @@ static void balloon_stats_set_poll_interval(Object
> > *obj, Visitor *v,
> > balloon_stats_change_timer(s, 0);
> > }
> >
> > +static void virtio_balloon_handle_report(VirtIODevice *vdev, VirtQueue *vq)
> > +{
> > + VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
> > + VirtQueueElement *elem;
> > +
> > + while ((elem = virtqueue_pop(vq, sizeof(VirtQueueElement)))) {
> > + unsigned int i;
> > +
> > + for (i = 0; i < elem->in_num; i++) {
> > + void *addr = elem->in_sg[i].iov_base;
> > + size_t size = elem->in_sg[i].iov_len;
> > + ram_addr_t ram_offset;
> > + size_t rb_page_size;
> > + RAMBlock *rb;
> > +
> > + if (qemu_balloon_is_inhibited() || dev->poison_val) {
> > + continue;
>
> actually, you want to do that in the outer loop, no?
I'll move that. Odds are compiler was doing that anyway.
> > + }
> > +
> > + /*
> > + * There is no need to check the memory section to see if
> > + * it is ram/readonly/romd like there is for handle_output
> > + * below. If the region is not meant to be written to then
> > + * address_space_map will have allocated a bounce buffer
> > + * and it will be freed in address_space_unmap and trigger
> > + * and unassigned_mem_write before failing to copy over the
> > + * buffer. If more than one bad descriptor is provided it
> > + * will return NULL after the first bounce buffer and fail
> > + * to map any resources.
> > + */
> > + rb = qemu_ram_block_from_host(addr, false, &ram_offset);
> > + if (!rb) {
> > + trace_virtio_balloon_bad_addr(elem->in_addr[i]);
> > + continue;
> > + }
> > +
> > + /* For now we will simply ignore unaligned memory regions */
> > + rb_page_size = qemu_ram_pagesize(rb);
> > + if (!QEMU_IS_ALIGNED(ram_offset | size, rb_page_size)) {
>
> /me thinks you can drop rb_page_size
You mean just fold it into the statement? I guess I can do that.
> I *think* there is still one remaining case to handle: Crossing RAM blocks.
>
> Most probably you should check
>
> /* For now, ignore crossing RAM blocks. */
> if (ram_offset + size >= qemu_ram_get_used_length()) {
> continue;
> }
>
> otherwise ram_block_discard_range() will report an error.
Makes sense. I can add that into the QEMU_IS_ALIGNED check.
- Re: [PATCH v19 QEMU 1/4] virtio-balloon: Implement support for page poison tracking feature, (continued)
- Re: [PATCH v19 QEMU 1/4] virtio-balloon: Implement support for page poison tracking feature, David Hildenbrand, 2020/04/16
- Re: [PATCH v19 QEMU 1/4] virtio-balloon: Implement support for page poison tracking feature, David Hildenbrand, 2020/04/16
- Re: [PATCH v19 QEMU 1/4] virtio-balloon: Implement support for page poison tracking feature, Michael S. Tsirkin, 2020/04/16
- Re: [PATCH v19 QEMU 1/4] virtio-balloon: Implement support for page poison tracking feature, David Hildenbrand, 2020/04/16
- Re: [PATCH v19 QEMU 1/4] virtio-balloon: Implement support for page poison tracking feature, Alexander Duyck, 2020/04/16
- Re: [PATCH v19 QEMU 1/4] virtio-balloon: Implement support for page poison tracking feature, David Hildenbrand, 2020/04/16
[PATCH v19 QEMU 2/4] linux-headers: update to contain virito-balloon free page reporting, Alexander Duyck, 2020/04/09
[PATCH v19 QEMU 3/4] virtio-balloon: Provide an interface for free page reporting, Alexander Duyck, 2020/04/09
[PATCH v19 QEMU 4/4] memory: Do not allow direct write access to rom_device regions, Alexander Duyck, 2020/04/09