Messages in this thread | | | Date | Fri, 28 Jul 2017 16:25:19 +0800 | From | Wei Wang <> | Subject | Re: [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG |
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On 07/12/2017 08:40 PM, Wei Wang wrote: > Add a new feature, VIRTIO_BALLOON_F_SG, which enables to > transfer a chunk of ballooned (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 ~491ms > resulting in an improvement of ~88%. >
I found a recent mm patch, bb01b64cfab7c22f3848cb73dc0c2b46b8d38499 , zeros all the ballooned pages, which is very time consuming.
Tests show that the time to balloon 7G pages is increased from ~491 ms to 2.8 seconds with the above patch.
How about moving the zero operation to the hypervisor? In this way, we will have a much faster balloon process.
Best, Wei
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