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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id p32sm25527072qtb.67.2019.07.25.07.54.47 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Thu, 25 Jul 2019 07:54:52 -0700 (PDT) Date: Thu, 25 Jul 2019 10:54:45 -0400 From: "Michael S. Tsirkin" To: Nitesh Narayan Lal Cc: Alexander Duyck , 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, alexander.h.duyck@linux.intel.com Subject: Re: [PATCH v2 5/5] virtio-balloon: Add support for providing page hints to host Message-ID: <20190725105415-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> <21cc88cd-3577-e8b4-376f-26c7848f5764@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <21cc88cd-3577-e8b4-376f-26c7848f5764@redhat.com> Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Jul 25, 2019 at 10:44:01AM -0400, Nitesh Narayan Lal wrote: > > On 7/24/19 3:02 PM, 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 ... > > > > > >> --- > >> 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 ... > > Do we need an error check here? > > For situations where this fails we should disable hinting completely, maybe? I would just limit this to vq size, then you know it won't fail. > > > > >> + 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. > > > > > > > >> +} > >> + > >> 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 ... > > > >> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) { > >> + err = page_hinting_startup(&vb->ph_dev_info); > >> + if (err) > >> + goto out_unregister_shrinker; > >> + } > >> + > >> virtio_device_ready(vdev); > >> > >> if (towards_target(vb)) > >> virtballoon_changed(vdev); > >> return 0; > >> > >> +out_unregister_shrinker: > >> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) > >> + virtio_balloon_unregister_shrinker(vb); > >> out_del_balloon_wq: > >> if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) > >> destroy_workqueue(vb->balloon_wq); > >> @@ -958,6 +1002,8 @@ static void virtballoon_remove(struct virtio_device *vdev) > >> { > >> struct virtio_balloon *vb = vdev->priv; > >> > >> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) > >> + page_hinting_shutdown(&vb->ph_dev_info); > >> if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) > >> virtio_balloon_unregister_shrinker(vb); > >> spin_lock_irq(&vb->stop_update_lock); > >> @@ -1027,6 +1073,7 @@ static int virtballoon_validate(struct virtio_device *vdev) > >> VIRTIO_BALLOON_F_DEFLATE_ON_OOM, > >> VIRTIO_BALLOON_F_FREE_PAGE_HINT, > >> VIRTIO_BALLOON_F_PAGE_POISON, > >> + VIRTIO_BALLOON_F_HINTING, > >> }; > >> > >> static struct virtio_driver virtio_balloon_driver = { > >> diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h > >> index a1966cd7b677..2b0f62814e22 100644 > >> --- a/include/uapi/linux/virtio_balloon.h > >> +++ b/include/uapi/linux/virtio_balloon.h > >> @@ -36,6 +36,7 @@ > >> #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */ > >> #define VIRTIO_BALLOON_F_FREE_PAGE_HINT 3 /* VQ to report free pages */ > >> #define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */ > >> +#define VIRTIO_BALLOON_F_HINTING 5 /* Page hinting virtqueue */ > >> > >> /* Size of a PFN in the balloon interface. */ > >> #define VIRTIO_BALLOON_PFN_SHIFT 12 > -- > Thanks > Nitesh