From: "Li, Liang Z" <liang.z.li@intel.com>
To: "Michael S. Tsirkin" <mst@redhat.com>,
"Hansen, Dave" <dave.hansen@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
David Hildenbrand <david@redhat.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"mhocko@suse.com" <mhocko@suse.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"dgilbert@redhat.com" <dgilbert@redhat.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>
Subject: RE: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration
Date: Fri, 16 Dec 2016 01:12:21 +0000 [thread overview]
Message-ID: <F2CBF3009FA73547804AE4C663CAB28E3C32A899@shsmsx102.ccr.corp.intel.com> (raw)
In-Reply-To: <20161215173901-mutt-send-email-mst@kernel.org>
> On Thu, Dec 15, 2016 at 07:34:33AM -0800, Dave Hansen wrote:
> > On 12/14/2016 12:59 AM, Li, Liang Z wrote:
> > >> Subject: Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend
> > >> virtio-balloon for fast (de)inflating & fast live migration
> > >>
> > >> On 12/08/2016 08:45 PM, Li, Liang Z wrote:
> > >>> What's the conclusion of your discussion? It seems you want some
> > >>> statistic before deciding whether to ripping the bitmap from the
> > >>> ABI, am I right?
> > >>
> > >> I think Andrea and David feel pretty strongly that we should remove
> > >> the bitmap, unless we have some data to support keeping it. I
> > >> don't feel as strongly about it, but I think their critique of it
> > >> is pretty valid. I think the consensus is that the bitmap needs to go.
> > >>
> > >> The only real question IMNHO is whether we should do a power-of-2
> > >> or a length. But, if we have 12 bits, then the argument for doing
> > >> length is pretty strong. We don't need anywhere near 12 bits if doing
> power-of-2.
> > >
> > > Just found the MAX_ORDER should be limited to 12 if use length
> > > instead of order, If the MAX_ORDER is configured to a value bigger
> > > than 12, it will make things more complex to handle this case.
> > >
> > > If use order, we need to break a large memory range whose length is
> > > not the power of 2 into several small ranges, it also make the code
> complex.
> >
> > I can't imagine it makes the code that much more complex. It adds a
> > for loop. Right?
> >
> > > It seems we leave too many bit for the pfn, and the bits leave for
> > > length is not enough, How about keep 45 bits for the pfn and 19 bits
> > > for length, 45 bits for pfn can cover 57 bits physical address, that should
> be enough in the near feature.
> > >
> > > What's your opinion?
> >
> > I still think 'order' makes a lot of sense. But, as you say, 57 bits
> > is enough for x86 for a while. Other architectures.... who knows?
>
> I think you can probably assume page size >= 4K. But I would not want to
> make any other assumptions. E.g. there are systems that absolutely require
> you to set high bits for DMA.
>
> I think we really want both length and order.
>
> I understand how you are trying to pack them as tightly as possible.
>
> However, I thought of a trick, we don't need to encode all possible orders.
> For example, with 2 bits of order, we can make them mean:
> 00 - 4K pages
> 01 - 2M pages
> 02 - 1G pages
>
> guest can program the sizes for each order through config space.
>
> We will have 10 bits left for legth.
>
Please don't, we just get rid of the bitmap for simplification. :)
> It might make sense to also allow guest to program the number of bits used
> for order, this will make it easy to extend without host changes.
>
There still exist the case if the MAX_ORDER is configured to a large value, e.g. 36 for a system
with huge amount of memory, then there is only 28 bits left for the pfn, which is not enough.
Should we limit the MAX_ORDER? I don't think so.
It seems use order is better.
Thanks!
Liang
> --
> MST
next prev parent reply other threads:[~2016-12-16 1:13 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-30 8:43 [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration Liang Li
2016-11-30 8:43 ` [PATCH kernel v5 1/5] virtio-balloon: rework deflate to add page to a list Liang Li
2016-11-30 8:43 ` [PATCH kernel v5 2/5] virtio-balloon: define new feature bit and head struct Liang Li
2016-11-30 8:43 ` [PATCH kernel v5 3/5] virtio-balloon: speed up inflate/deflate process Liang Li
2016-11-30 8:43 ` [PATCH kernel v5 4/5] virtio-balloon: define flags and head for host request vq Liang Li
2016-11-30 8:43 ` [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused page info Liang Li
2016-11-30 19:15 ` Dave Hansen
2016-12-04 13:13 ` Li, Liang Z
2016-12-05 17:22 ` Dave Hansen
2016-12-06 4:47 ` Li, Liang Z
2016-12-06 8:40 ` [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration David Hildenbrand
2016-12-07 13:35 ` Li, Liang Z
2016-12-07 15:34 ` Dave Hansen
2016-12-09 3:09 ` Li, Liang Z
2016-12-07 15:42 ` David Hildenbrand
2016-12-07 15:45 ` Dave Hansen
2016-12-07 16:21 ` David Hildenbrand
2016-12-07 16:57 ` Dave Hansen
2016-12-07 18:38 ` [Qemu-devel] " Andrea Arcangeli
2016-12-07 18:44 ` Dave Hansen
2016-12-07 18:58 ` Andrea Arcangeli
2016-12-07 19:54 ` Dave Hansen
2016-12-07 20:28 ` Andrea Arcangeli
2016-12-09 4:45 ` Li, Liang Z
2016-12-09 4:53 ` Dave Hansen
2016-12-09 5:35 ` Li, Liang Z
2016-12-09 16:42 ` Andrea Arcangeli
2016-12-14 8:20 ` Li, Liang Z
2016-12-14 8:59 ` Li, Liang Z
2016-12-15 15:34 ` Dave Hansen
2016-12-15 15:54 ` Michael S. Tsirkin
2016-12-16 1:12 ` Li, Liang Z [this message]
2016-12-16 15:40 ` Andrea Arcangeli
2016-12-17 11:56 ` Li, Liang Z
2016-12-16 0:48 ` Li, Liang Z
2016-12-16 1:09 ` Dave Hansen
2016-12-16 1:38 ` Li, Liang Z
2016-12-16 1:40 ` Dave Hansen
2016-12-16 1:43 ` Li, Liang Z
2016-12-16 16:01 ` Andrea Arcangeli
2016-12-17 12:39 ` Li, Liang Z
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