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[79.181.91.42]) by smtp.gmail.com with ESMTPSA id g2sm21591961qti.68.2019.07.24.14.39.00 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Wed, 24 Jul 2019 14:39:04 -0700 (PDT) Date: Wed, 24 Jul 2019 17:38:57 -0400 From: "Michael S. Tsirkin" To: Alexander Duyck Cc: 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, alexander.h.duyck@linux.intel.com Subject: Re: [PATCH v2 QEMU] virtio-balloon: Provide a interface for "bubble hinting" Message-ID: <20190724173403-mutt-send-email-mst@kernel.org> References: <20190724165158.6685.87228.stgit@localhost.localdomain> <20190724171050.7888.62199.stgit@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190724171050.7888.62199.stgit@localhost.localdomain> 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 10:12:10AM -0700, Alexander Duyck wrote: > From: Alexander Duyck > > Add support for what I am referring to as "bubble hinting". Basically 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 is meant to be a simplification of the existing balloon interface > to use for providing hints to what memory needs to be freed. I am assuming > this is safe to do as the deflate logic does not actually appear to do very > much other than tracking what subpages have been released and which ones > haven't. > > Signed-off-by: Alexander Duyck BTW I wonder about migration here. When we migrate we lose all hints right? Well destination could be smarter, detect that page is full of 0s and just map a zero page. Then we don't need a hint as such - but I don't think it's done like that ATM. I also wonder about interaction with deflate. ATM deflate will add pages to the free list, then balloon will come right back and report them as free. > --- > hw/virtio/virtio-balloon.c | 40 +++++++++++++++++++++++ > include/hw/virtio/virtio-balloon.h | 2 + > include/standard-headers/linux/virtio_balloon.h | 1 + > 3 files changed, 42 insertions(+), 1 deletion(-) > > diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c > index 2112874055fb..70c0004c0f88 100644 > --- a/hw/virtio/virtio-balloon.c > +++ b/hw/virtio/virtio-balloon.c > @@ -328,6 +328,39 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v, > balloon_stats_change_timer(s, 0); > } > > +static void virtio_bubble_handle_output(VirtIODevice *vdev, VirtQueue *vq) > +{ > + 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()) > + continue; > + > + rb = qemu_ram_block_from_host(addr, false, &ram_offset); > + rb_page_size = qemu_ram_pagesize(rb); > + > + /* For now we will simply ignore unaligned memory regions */ > + if ((ram_offset | size) & (rb_page_size - 1)) > + continue; > + > + ram_block_discard_range(rb, ram_offset, size); > + } > + > + virtqueue_push(vq, elem, 0); > + virtio_notify(vdev, vq); > + g_free(elem); > + } > +} > + > static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq) > { > VirtIOBalloon *s = VIRTIO_BALLOON(vdev); > @@ -782,6 +815,11 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp) > s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); > > if (virtio_has_feature(s->host_features, > + VIRTIO_BALLOON_F_HINTING)) { > + s->hvq = virtio_add_queue(vdev, 128, virtio_bubble_handle_output); > + } > + > + if (virtio_has_feature(s->host_features, > VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { > s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, > virtio_balloon_handle_free_page_vq); > @@ -897,6 +935,8 @@ static Property virtio_balloon_properties[] = { > VIRTIO_BALLOON_F_DEFLATE_ON_OOM, false), > DEFINE_PROP_BIT("free-page-hint", VirtIOBalloon, host_features, > VIRTIO_BALLOON_F_FREE_PAGE_HINT, false), > + DEFINE_PROP_BIT("guest-page-hinting", VirtIOBalloon, host_features, > + VIRTIO_BALLOON_F_HINTING, true), > DEFINE_PROP_LINK("iothread", VirtIOBalloon, iothread, TYPE_IOTHREAD, > IOThread *), > DEFINE_PROP_END_OF_LIST(), > diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h > index 1afafb12f6bc..a58b24fdf29d 100644 > --- a/include/hw/virtio/virtio-balloon.h > +++ b/include/hw/virtio/virtio-balloon.h > @@ -44,7 +44,7 @@ enum virtio_balloon_free_page_report_status { > > typedef struct VirtIOBalloon { > VirtIODevice parent_obj; > - VirtQueue *ivq, *dvq, *svq, *free_page_vq; > + VirtQueue *ivq, *dvq, *svq, *free_page_vq, *hvq; > uint32_t free_page_report_status; > uint32_t num_pages; > uint32_t actual; > diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h > index 9375ca2a70de..f9e3e8256261 100644 > --- a/include/standard-headers/linux/virtio_balloon.h > +++ b/include/standard-headers/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