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From: "Michael S. Tsirkin" <mst@redhat.com>
To: Wei Wang <wei.w.wang@intel.com>
Cc: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
	virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
	linux-mm@kvack.org, david@redhat.com, cornelia.huck@de.ibm.com,
	akpm@linux-foundation.org, mgorman@techsingularity.net,
	aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com,
	liliang.opensource@gmail.com, mhocko@kernel.org,
	willy@infradead.org, virtio-dev@lists.oasis-open.org,
	yang.zhang.wz@gmail.com, quan.xu@aliyun.com
Subject: Re: [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG
Date: Sat, 29 Jul 2017 02:01:35 +0300	[thread overview]
Message-ID: <20170729020006-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <597AF4EF.4020705@intel.com>

On Fri, Jul 28, 2017 at 04:25:19PM +0800, Wei Wang wrote:
> 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.

Sounds like it should be reverted. Post a revert pls and
we'll discuss.

> How about moving the zero operation to the hypervisor? In this way, we
> will have a much faster balloon process.
> 
> 
> Best,
> Wei

Or in other words hypervisors should not be stupid and
should not try to run ksm on DONTNEED pages.

-- 
MST

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  reply	other threads:[~2017-07-28 23:01 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-12 12:40 [PATCH v12 0/8] Virtio-balloon Enhancement Wei Wang
2017-07-12 12:40 ` [PATCH v12 1/8] virtio-balloon: deflate via a page list Wei Wang
2017-07-12 12:40 ` [PATCH v12 2/8] virtio-balloon: coding format cleanup Wei Wang
2017-07-12 12:40 ` [PATCH v12 3/8] Introduce xbitmap Wei Wang
2017-07-12 12:40 ` [PATCH v12 4/8] xbitmap: add xb_find_next_bit() and xb_zero() Wei Wang
2017-07-12 12:40 ` [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG Wei Wang
2017-07-12 13:06   ` Michael S. Tsirkin
2017-07-12 13:29     ` Wei Wang
2017-07-12 13:56       ` Michael S. Tsirkin
2017-07-13  7:42         ` Wei Wang
2017-07-13 20:19           ` Michael S. Tsirkin
2017-07-14  7:12             ` Wei Wang
2017-07-23  1:45               ` Michael S. Tsirkin
2017-07-26  3:48                 ` Wei Wang
2017-07-26 17:02                   ` Michael S. Tsirkin
2017-07-27  2:50                     ` Wei Wang
2017-07-28 23:08                       ` Michael S. Tsirkin
2017-07-29 12:47                         ` Wei Wang
2017-07-30  4:22                           ` Michael S. Tsirkin
2017-07-30  5:59                             ` Wang, Wei W
2017-07-30 16:18                               ` Michael S. Tsirkin
2017-07-30 16:20                                 ` Michael S. Tsirkin
2017-07-31 12:36                                   ` Wei Wang
2017-07-13  0:44   ` Michael S. Tsirkin
2017-07-13  1:16   ` kbuild test robot
2017-07-13  4:21   ` kbuild test robot
2017-07-28  8:25   ` Wei Wang
2017-07-28 23:01     ` Michael S. Tsirkin [this message]
2017-07-12 12:40 ` [PATCH v12 6/8] mm: support reporting free page blocks Wei Wang
2017-07-13  0:33   ` Michael S. Tsirkin
2017-07-13  8:25     ` Wei Wang
2017-07-14 12:30   ` Michal Hocko
2017-07-14 12:54     ` Michal Hocko
2017-07-14 15:46       ` Michael S. Tsirkin
2017-07-14 19:17     ` Michael S. Tsirkin
2017-07-17 15:24       ` Michal Hocko
2017-07-18  2:12         ` Wei Wang
2017-07-19  8:13           ` Michal Hocko
2017-07-19 12:01             ` Wei Wang
2017-07-24  9:00               ` Michal Hocko
2017-07-25  9:32                 ` Wei Wang
2017-07-25 11:25                   ` Michal Hocko
2017-07-25 11:56                     ` Wei Wang
2017-07-25 12:41                       ` Michal Hocko
2017-07-25 14:47                         ` Wang, Wei W
2017-07-25 14:53                           ` Michal Hocko
2017-07-26  2:22                             ` Wei Wang
2017-07-26 10:24                               ` Michal Hocko
2017-07-26 11:44                                 ` Wei Wang
2017-07-26 11:55                                   ` Michal Hocko
2017-07-26 12:47                                     ` Wang, Wei W
2017-07-12 12:40 ` [PATCH v12 7/8] mm: export symbol of next_zone and first_online_pgdat Wei Wang
2017-07-13  0:16   ` Michael S. Tsirkin
2017-07-13  8:41     ` [virtio-dev] " Wei Wang
2017-07-14 12:31   ` Michal Hocko
2017-07-12 12:40 ` [PATCH v12 8/8] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ Wei Wang
2017-07-13  0:22   ` Michael S. Tsirkin
2017-07-13  8:46     ` Wei Wang
2017-07-13 17:59       ` Michael S. Tsirkin
2017-07-13  0:14 ` [PATCH v12 0/8] Virtio-balloon Enhancement Michael S. Tsirkin

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