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:   Wed, 14 Dec 2016 08:59:47 +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 12/08/2016 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.

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?


thanks!
Liang