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Tsirkin" To: Alexander Duyck Cc: Nitesh Narayan Lal , kvm list , David Hildenbrand , Dave Hansen , LKML , linux-mm , Andrew Morton , Yang Zhang , pagupta@redhat.com, Rik van Riel , Konrad Rzeszutek Wilk , lcapitulino@redhat.com, wei.w.wang@intel.com, Andrea Arcangeli , Paolo Bonzini , dan.j.williams@intel.com, Alexander Duyck Subject: Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory via hinting Message-ID: <20190716115535-mutt-send-email-mst@kernel.org> References: <20190619222922.1231.27432.stgit@localhost.localdomain> <20190619223338.1231.52537.stgit@localhost.localdomain> <20190716055017-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 16 Jul 2019 16:08:02 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 16, 2019 at 08:37:06AM -0700, Alexander Duyck wrote: > On Tue, Jul 16, 2019 at 2:55 AM Michael S. Tsirkin wrote: > > > > On Wed, Jun 19, 2019 at 03:33:38PM -0700, Alexander Duyck wrote: > > > From: Alexander Duyck > > > > > > Add support for aerating memory using the 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 > > > --- > > > drivers/virtio/Kconfig | 1 > > > drivers/virtio/virtio_balloon.c | 110 ++++++++++++++++++++++++++++++++++- > > > include/uapi/linux/virtio_balloon.h | 1 > > > 3 files changed, 108 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig > > > index 023fc3bc01c6..9cdaccf92c3a 100644 > > > --- a/drivers/virtio/Kconfig > > > +++ b/drivers/virtio/Kconfig > > > @@ -47,6 +47,7 @@ config VIRTIO_BALLOON > > > tristate "Virtio balloon driver" > > > depends on VIRTIO > > > select MEMORY_BALLOON > > > + select AERATION > > > ---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 44339fc87cc7..91f1e8c9017d 100644 > > > --- a/drivers/virtio/virtio_balloon.c > > > +++ b/drivers/virtio/virtio_balloon.c > > > @@ -18,6 +18,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > /* > > > * Balloon device works in 4K page units. So each page is pointed to by > > > @@ -26,6 +27,7 @@ > > > */ > > > #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 | \ > > > @@ -45,6 +47,7 @@ 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 > > > }; > > > > > > @@ -54,7 +57,8 @@ enum virtio_balloon_config_read { > > > > > > struct virtio_balloon { > > > struct virtio_device *vdev; > > > - struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq; > > > + struct virtqueue *inflate_vq, *deflate_vq, *stats_vq, *free_page_vq, > > > + *hinting_vq; > > > > > > /* Balloon's own wq for cpu-intensive work items */ > > > struct workqueue_struct *balloon_wq; > > > @@ -103,9 +107,21 @@ struct virtio_balloon { > > > /* Synchronize access/update to this struct virtio_balloon elements */ > > > struct mutex balloon_lock; > > > > > > - /* The array of pfns we tell the Host about. */ > > > - unsigned int num_pfns; > > > - __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX]; > > > + > > > + union { > > > + /* The array of pfns we tell the Host about. */ > > > + struct { > > > + unsigned int num_pfns; > > > + __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX]; > > > + }; > > > + /* The array of physical addresses we are hinting on */ > > > + struct { > > > + unsigned int num_hints; > > > + __virtio64 hints[VIRTIO_BALLOON_ARRAY_HINTS_MAX]; > > > + }; > > > + }; > > > + > > > + struct aerator_dev_info a_dev_info; > > > > > > /* Memory statistics */ > > > struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; > > > @@ -151,6 +167,68 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq) > > > > > > } > > > > > > +static u64 page_to_hints_pa_order(struct page *page) > > > +{ > > > + unsigned char order; > > > + dma_addr_t pa; > > > + > > > + BUILD_BUG_ON((64 - VIRTIO_BALLOON_PFN_SHIFT) >= > > > + (1 << VIRTIO_BALLOON_PFN_SHIFT)); > > > + > > > + /* > > > + * Record physical page address combined with page order. > > > + * Order will never exceed 64 - VIRTIO_BALLON_PFN_SHIFT > > > + * since the size has to fit into a 64b value. So as long > > > + * as VIRTIO_BALLOON_SHIFT is greater than this combining > > > + * the two values should be safe. > > > + */ > > > + pa = page_to_phys(page); > > > + order = page_private(page) + > > > + PAGE_SHIFT - VIRTIO_BALLOON_PFN_SHIFT; > > > + > > > + return (u64)(pa | order); > > > +} > > > + > > > +void virtballoon_aerator_react(struct aerator_dev_info *a_dev_info) > > > +{ > > > + struct virtio_balloon *vb = container_of(a_dev_info, > > > + struct virtio_balloon, > > > + a_dev_info); > > > + struct virtqueue *vq = vb->hinting_vq; > > > + struct scatterlist sg; > > > + unsigned int unused; > > > + struct page *page; > > > + > > > + mutex_lock(&vb->balloon_lock); > > > + > > > + vb->num_hints = 0; > > > + > > > + list_for_each_entry(page, &a_dev_info->batch, lru) { > > > + vb->hints[vb->num_hints++] = > > > + cpu_to_virtio64(vb->vdev, > > > + page_to_hints_pa_order(page)); > > > + } > > > + > > > + /* We shouldn't have been called if there is nothing to process */ > > > + if (WARN_ON(vb->num_hints == 0)) > > > + goto out; > > > + > > > + sg_init_one(&sg, vb->hints, > > > + sizeof(vb->hints[0]) * vb->num_hints); > > > + > > > + /* > > > + * We should always be able to add one buffer to an > > > + * empty queue. > > > + */ > > > + virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); > > > + virtqueue_kick(vq); > > > + > > > + /* When host has read buffer, this completes via balloon_ack */ > > > + wait_event(vb->acked, virtqueue_get_buf(vq, &unused)); > > > +out: > > > + mutex_unlock(&vb->balloon_lock); > > > +} > > > + > > > static void set_page_pfns(struct virtio_balloon *vb, > > > __virtio32 pfns[], struct page *page) > > > { > > > @@ -475,6 +553,7 @@ 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"; > > > @@ -486,11 +565,19 @@ 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)) { > > > @@ -929,12 +1016,24 @@ static int virtballoon_probe(struct virtio_device *vdev) > > > if (err) > > > goto out_del_balloon_wq; > > > } > > > + > > > + vb->a_dev_info.react = virtballoon_aerator_react; > > > + vb->a_dev_info.capacity = VIRTIO_BALLOON_ARRAY_HINTS_MAX; > > > + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) { > > > + err = aerator_startup(&vb->a_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); > > > @@ -963,6 +1062,8 @@ static void virtballoon_remove(struct virtio_device *vdev) > > > { > > > struct virtio_balloon *vb = vdev->priv; > > > > > > + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_HINTING)) > > > + aerator_shutdown(); > > > if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) > > > virtio_balloon_unregister_shrinker(vb); > > > spin_lock_irq(&vb->stop_update_lock); > > > @@ -1032,6 +1133,7 @@ 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 > > > > > > > > The approach here is very close to what on-demand hinting that is > > already upstream does. > > > > This should have resulted in a most of the code being shared > > but this does not seem to happen here. > > > > Can we unify the code in some way? > > It can still use a separate feature flag, but there are things > > I like very much about current hinting code, such as > > using s/g instead of passing PFNs in a buffer. > > > > If this doesn't work could you elaborate on why? > > As far as sending a scatter gather that shouldn't be too much of an > issue, however I need to double check that I will still be able to > keep the completions as a single block. > > One significant spot where the "VIRTIO_BALLOON_F_FREE_PAGE_HINT" code > and my code differs. My code is processing a fixed discreet block of > pages at a time, whereas the FREE_PAGE_HINT code is slurping up all > available high-order memory and stuffing it into a giant balloon and > has more of a streaming setup as it doesn't return things until either > forced to by the shrinker or once it has processed all available > memory. This is what I am saying. Having watched that patchset being developed, I think that's simply because processing blocks required mm core changes, which Wei was not up to pushing through. If we did while (1) { alloc_pages add_buf get_buf free_pages } We'd end up passing the same page to balloon again and again. So we end up reserving lots of memory with alloc_pages instead. What I am saying is that now that you are developing infrastructure to iterate over free pages, FREE_PAGE_HINT should be able to use it too. Whether that's possible might be a good indication of whether the new mm APIs make sense. > The basic idea with the bubble hinting was to essentially create mini > balloons. As such I had based the code off of the balloon inflation > code. The only spot where it really differs is that I needed the > ability to pass higher order pages so I tweaked thinks and passed > "hints" instead of "pfns". And that is fine. But there isn't really such a big difference with FREE_PAGE_HINT except FREE_PAGE_HINT triggers upon host request and not in response to guest load. -- MST