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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id b23sm29124888qte.19.2019.07.24.13.43.42 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 24 Jul 2019 13:43:46 -0700 (PDT) Date: Wed, 24 Jul 2019 16:43:39 -0400 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: Alexander Duyck , 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 Message-ID: <20190724164255-mutt-send-email-mst@kernel.org> References: <20190724165158.6685.87228.stgit@localhost.localdomain> <20190724170514.6685.17161.stgit@localhost.localdomain> <20190724143902-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 > > > > > > 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 > > > > 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 > > > #include > > > #include > > > +#include > > > > > > /* > > > * 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? > >