linux-kernel - RE: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration

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Date:   Fri, 16 Dec 2016 00:48:07 +0000
From:   "Li, Liang Z" <liang.z.li@...el.com>
To:     "Hansen, Dave" <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>
CC:     David Hildenbrand <david@...hat.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mhocko@...e.com" <mhocko@...e.com>,
        "mst@...hat.com" <mst@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "dgilbert@...hat.com" <dgilbert@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
Subject: RE: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for
 fast (de)inflating & fast live migration

> Subject: Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for
> fast (de)inflating & fast live migration
> 
> 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?
> 

Yes, just a little. :)

> > 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?

Yes.