From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v15 3/5] virtio-balloon: VIRTIO_BALLOON_F_SG Date: Mon, 28 Aug 2017 21:03:34 +0300 Message-ID: <20170828204659-mutt-send-email-mst__9178.53536452657$1503943455$gmane$org@kernel.org> References: <1503914913-28893-1-git-send-email-wei.w.wang@intel.com> <1503914913-28893-4-git-send-email-wei.w.wang@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1503914913-28893-4-git-send-email-wei.w.wang@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Wei Wang Cc: aarcange@redhat.com, virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org, mawilcox@microsoft.com, qemu-devel@nongnu.org, amit.shah@redhat.com, liliang.opensource@gmail.com, linux-kernel@vger.kernel.org, willy@infradead.org, virtualization@lists.linux-foundation.org, linux-mm@kvack.org, yang.zhang.wz@gmail.com, quan.xu@aliyun.com, cornelia.huck@de.ibm.com, pbonzini@redhat.com, akpm@linux-foundation.org, mhocko@kernel.org, mgorman@techsingularity.net List-Id: virtualization@lists.linuxfoundation.org On Mon, Aug 28, 2017 at 06:08:31PM +0800, Wei Wang wrote: > Add a new feature, VIRTIO_BALLOON_F_SG, which enables the transfer > of balloon (i.e. inflated/deflated) pages using scatter-gather lists > to the host. > > The implementation of the previous virtio-balloon is not very > efficient, because the balloon pages are transferred to the > host one by one. Here is the breakdown of the time in percentage > spent on each step of the balloon inflating process (inflating > 7GB of an 8GB idle guest). > > 1) allocating pages (6.5%) > 2) sending PFNs to host (68.3%) > 3) address translation (6.1%) > 4) madvise (19%) > > It takes about 4126ms for the inflating process to complete. > The above profiling shows that the bottlenecks are stage 2) > and stage 4). > > This patch optimizes step 2) by transferring pages to the host in > sgs. An sg describes a chunk of guest physically continuous pages. > With this mechanism, step 4) can also be optimized by doing address > translation and madvise() in chunks rather than page by page. > > With this new feature, the above ballooning process takes ~597ms > resulting in an improvement of ~86%. > > TODO: optimize stage 1) by allocating/freeing a chunk of pages > instead of a single page each time. > > Signed-off-by: Wei Wang > Signed-off-by: Liang Li > Suggested-by: Michael S. Tsirkin > --- > drivers/virtio/virtio_balloon.c | 171 ++++++++++++++++++++++++++++++++---- > include/uapi/linux/virtio_balloon.h | 1 + > 2 files changed, 155 insertions(+), 17 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index f0b3a0b..8ecc1d4 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -32,6 +32,8 @@ > #include > #include > #include > +#include > +#include > > /* > * Balloon device works in 4K page units. So each page is pointed to by > @@ -79,6 +81,9 @@ struct virtio_balloon { > /* Synchronize access/update to this struct virtio_balloon elements */ > struct mutex balloon_lock; > > + /* The xbitmap used to record balloon pages */ > + struct xb page_xb; > + > /* The array of pfns we tell the Host about. */ > unsigned int num_pfns; > __virtio32 pfns[VIRTIO_BALLOON_ARRAY_PFNS_MAX]; > @@ -141,13 +146,111 @@ static void set_page_pfns(struct virtio_balloon *vb, > page_to_balloon_pfn(page) + i); > } > > +static int add_one_sg(struct virtqueue *vq, void *addr, uint32_t size) > +{ > + struct scatterlist sg; > + > + sg_init_one(&sg, addr, size); > + return virtqueue_add_inbuf(vq, &sg, 1, vq, GFP_KERNEL); > +} > + > +static void send_balloon_page_sg(struct virtio_balloon *vb, > + struct virtqueue *vq, > + void *addr, > + uint32_t size, > + bool batch) > +{ > + unsigned int len; > + int err; > + > + err = add_one_sg(vq, addr, size); > + /* Sanity check: this can't really happen */ > + WARN_ON(err); It might be cleaner to detect that add failed due to ring full and kick then. Just an idea, up to you whether to do it. > + > + /* If batching is in use, we batch the sgs till the vq is full. */ > + if (!batch || !vq->num_free) { > + virtqueue_kick(vq); > + wait_event(vb->acked, virtqueue_get_buf(vq, &len)); > + /* Release all the entries if there are */ Meaning Account for all used entries if any ? > + while (virtqueue_get_buf(vq, &len)) > + ; Above code is reused below. Add a function? > + } > +} > + > +/* > + * Send balloon pages in sgs to host. The balloon pages are recorded in the > + * page xbitmap. Each bit in the bitmap corresponds to a page of PAGE_SIZE. > + * The page xbitmap is searched for continuous "1" bits, which correspond > + * to continuous pages, to chunk into sgs. > + * > + * @page_xb_start and @page_xb_end form the range of bits in the xbitmap that > + * need to be searched. > + */ > +static void tell_host_sgs(struct virtio_balloon *vb, > + struct virtqueue *vq, > + unsigned long page_xb_start, > + unsigned long page_xb_end) > +{ > + unsigned long sg_pfn_start, sg_pfn_end; > + void *sg_addr; > + uint32_t sg_len, sg_max_len = round_down(UINT_MAX, PAGE_SIZE); > + > + sg_pfn_start = page_xb_start; > + while (sg_pfn_start < page_xb_end) { > + sg_pfn_start = xb_find_next_bit(&vb->page_xb, sg_pfn_start, > + page_xb_end, 1); > + if (sg_pfn_start == page_xb_end + 1) > + break; > + sg_pfn_end = xb_find_next_bit(&vb->page_xb, sg_pfn_start + 1, > + page_xb_end, 0); > + sg_addr = (void *)pfn_to_kaddr(sg_pfn_start); > + sg_len = (sg_pfn_end - sg_pfn_start) << PAGE_SHIFT; > + while (sg_len > sg_max_len) { > + send_balloon_page_sg(vb, vq, sg_addr, sg_max_len, 1); Last argument should be true, not 1. > + sg_addr += sg_max_len; > + sg_len -= sg_max_len; > + } > + send_balloon_page_sg(vb, vq, sg_addr, sg_len, 1); > + xb_zero(&vb->page_xb, sg_pfn_start, sg_pfn_end); > + sg_pfn_start = sg_pfn_end + 1; > + } > + > + /* > + * The last few sgs may not reach the batch size, but need a kick to > + * notify the device to handle them. > + */ > + if (vq->num_free != virtqueue_get_vring_size(vq)) { > + virtqueue_kick(vq); > + wait_event(vb->acked, virtqueue_get_buf(vq, &sg_len)); > + while (virtqueue_get_buf(vq, &sg_len)) > + ; Some entries can get used after a pause. Looks like they will leak then? One fix would be to convert above if to a while loop. I don't know whether to do it like this in send_balloon_page_sg too. > + } > +} > + > +static inline void xb_set_page(struct virtio_balloon *vb, > + struct page *page, > + unsigned long *pfn_min, > + unsigned long *pfn_max) > +{ > + unsigned long pfn = page_to_pfn(page); > + > + *pfn_min = min(pfn, *pfn_min); > + *pfn_max = max(pfn, *pfn_max); > + xb_preload(GFP_KERNEL); > + xb_set_bit(&vb->page_xb, pfn); > + xb_preload_end(); > +} > + > static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) > { > struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info; > unsigned num_allocated_pages; > + bool use_sg = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_SG); > + unsigned long pfn_max = 0, pfn_min = ULONG_MAX; > > /* We can only do one array worth at a time. */ > - num = min(num, ARRAY_SIZE(vb->pfns)); > + if (!use_sg) > + num = min(num, ARRAY_SIZE(vb->pfns)); > > mutex_lock(&vb->balloon_lock); > for (vb->num_pfns = 0; vb->num_pfns < num; > @@ -162,7 +265,12 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) > msleep(200); > break; > } > - set_page_pfns(vb, vb->pfns + vb->num_pfns, page); > + > + if (use_sg) > + xb_set_page(vb, page, &pfn_min, &pfn_max); > + else > + set_page_pfns(vb, vb->pfns + vb->num_pfns, page); > + > vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE; > if (!virtio_has_feature(vb->vdev, > VIRTIO_BALLOON_F_DEFLATE_ON_OOM)) > @@ -171,8 +279,12 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num) > > num_allocated_pages = vb->num_pfns; > /* Did we get any? */ > - if (vb->num_pfns != 0) > - tell_host(vb, vb->inflate_vq); > + if (vb->num_pfns) { > + if (use_sg) > + tell_host_sgs(vb, vb->inflate_vq, pfn_min, pfn_max); > + else > + tell_host(vb, vb->inflate_vq); > + } > mutex_unlock(&vb->balloon_lock); > > return num_allocated_pages; > @@ -198,9 +310,12 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) > struct page *page; > struct balloon_dev_info *vb_dev_info = &vb->vb_dev_info; > LIST_HEAD(pages); > + bool use_sg = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_SG); > + unsigned long pfn_max = 0, pfn_min = ULONG_MAX; > > - /* We can only do one array worth at a time. */ > - num = min(num, ARRAY_SIZE(vb->pfns)); > + /* Traditionally, we can only do one array worth at a time. */ > + if (!use_sg) > + num = min(num, ARRAY_SIZE(vb->pfns)); > > mutex_lock(&vb->balloon_lock); > /* We can't release more pages than taken */ > @@ -210,7 +325,11 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) > page = balloon_page_dequeue(vb_dev_info); > if (!page) > break; > - set_page_pfns(vb, vb->pfns + vb->num_pfns, page); > + if (use_sg) > + xb_set_page(vb, page, &pfn_min, &pfn_max); > + else > + set_page_pfns(vb, vb->pfns + vb->num_pfns, page); > + > list_add(&page->lru, &pages); > vb->num_pages -= VIRTIO_BALLOON_PAGES_PER_PAGE; > } > @@ -221,8 +340,12 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num) > * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST); > * is true, we *have* to do it in this order > */ > - if (vb->num_pfns != 0) > - tell_host(vb, vb->deflate_vq); > + if (vb->num_pfns) { > + if (use_sg) > + tell_host_sgs(vb, vb->deflate_vq, pfn_min, pfn_max); > + else > + tell_host(vb, vb->deflate_vq); > + } > release_pages_balloon(vb, &pages); > mutex_unlock(&vb->balloon_lock); > return num_freed_pages; > @@ -441,6 +564,7 @@ static int init_vqs(struct virtio_balloon *vb) > } > > #ifdef CONFIG_BALLOON_COMPACTION > + > /* > * virtballoon_migratepage - perform the balloon page migration on behalf of > * a compation thread. (called under page lock) > @@ -464,6 +588,7 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info, > { > struct virtio_balloon *vb = container_of(vb_dev_info, > struct virtio_balloon, vb_dev_info); > + bool use_sg = virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_SG); > unsigned long flags; > > /* > @@ -485,16 +610,24 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info, > vb_dev_info->isolated_pages--; > __count_vm_event(BALLOON_MIGRATE); > spin_unlock_irqrestore(&vb_dev_info->pages_lock, flags); > - vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; > - set_page_pfns(vb, vb->pfns, newpage); > - tell_host(vb, vb->inflate_vq); > - > + if (use_sg) { > + send_balloon_page_sg(vb, vb->inflate_vq, page_address(newpage), > + PAGE_SIZE, 0); > + } else { > + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; > + set_page_pfns(vb, vb->pfns, newpage); > + tell_host(vb, vb->inflate_vq); > + } > /* balloon's page migration 2nd step -- deflate "page" */ > balloon_page_delete(page); > - vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; > - set_page_pfns(vb, vb->pfns, page); > - tell_host(vb, vb->deflate_vq); > - > + if (use_sg) { > + send_balloon_page_sg(vb, vb->deflate_vq, page_address(page), > + PAGE_SIZE, 0); > + } else { > + vb->num_pfns = VIRTIO_BALLOON_PAGES_PER_PAGE; > + set_page_pfns(vb, vb->pfns, page); > + tell_host(vb, vb->deflate_vq); > + } > mutex_unlock(&vb->balloon_lock); > > put_page(page); /* balloon reference */ > @@ -553,6 +686,9 @@ static int virtballoon_probe(struct virtio_device *vdev) > if (err) > goto out_free_vb; > > + if (virtio_has_feature(vdev, VIRTIO_BALLOON_F_SG)) > + xb_init(&vb->page_xb); > + > vb->nb.notifier_call = virtballoon_oom_notify; > vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY; > err = register_oom_notifier(&vb->nb); > @@ -669,6 +805,7 @@ static unsigned int features[] = { > VIRTIO_BALLOON_F_MUST_TELL_HOST, > VIRTIO_BALLOON_F_STATS_VQ, > VIRTIO_BALLOON_F_DEFLATE_ON_OOM, > + VIRTIO_BALLOON_F_SG, > }; > > static struct virtio_driver virtio_balloon_driver = { > diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h > index 343d7dd..37780a7 100644 > --- a/include/uapi/linux/virtio_balloon.h > +++ b/include/uapi/linux/virtio_balloon.h > @@ -34,6 +34,7 @@ > #define VIRTIO_BALLOON_F_MUST_TELL_HOST 0 /* Tell before reclaiming pages */ > #define VIRTIO_BALLOON_F_STATS_VQ 1 /* Memory Stats virtqueue */ > #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */ > +#define VIRTIO_BALLOON_F_SG 3 /* Use sg instead of PFN lists */ > > /* Size of a PFN in the balloon interface. */ > #define VIRTIO_BALLOON_PFN_SHIFT 12 > -- > 2.7.4