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

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On Wed, Dec 07, 2016 at 10:44:31AM -0800, Dave Hansen wrote:
> On 12/07/2016 10:38 AM, Andrea Arcangeli wrote:
> >> > and leaves room for the bitmap size to be encoded as well, if we decide
> >> > we need a bitmap in the future.
> > How would a bitmap ever be useful with very large page-order?
> 
> Please, guys.  Read the patches.  *Please*.

I did read the code but you didn't answer my question.

Why should a feature exist in the code that will never be useful. Why
do you think we could ever decide we'll need the bitmap in the future
for high order pages?

> The current code doesn't even _use_ a bitmap.

It's not using it right now, my question is exactly when it will ever
use it?

Leaving the bitmap only for order 0 allocations when you already wiped
all high pages orders from the buddy, doesn't seem very good idea
overall as the chance you got order 0 pages with close physical
address doesn't seem very high. It would be high if the loop that eat
into every possible higher order didn't run first, but such loop just
run and already wiped everything.

Also note, we need to call compaction very aggressive before falling
back from order 9 down to order 8. Ideally we should never use the
page_shift = PAGE_SHIFT case at all! Which leaves the bitmap as best
as an optimization for something that is suboptimal case already. If
the bitmap starts to payoff it means the admin did a mistake and
shrunk the guest too much.

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[PATCH kernel v5 0/5] Extend virtio-balloon for fast (de)inflating & fast live migration Liang Li <liang.z.li@intel.com> - 2016-11-30 10:00 +0100
  [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused page info Liang Li <liang.z.li@intel.com> - 2016-11-30 10:00 +0100
    Re: [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused page  info Dave Hansen <dave.hansen@intel.com> - 2016-11-30 20:20 +0100
      RE: [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused  page info "Li, Liang Z" <liang.z.li@intel.com> - 2016-12-04 14:20 +0100
        Re: [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused page  info Dave Hansen <dave.hansen@intel.com> - 2016-12-05 18:30 +0100
          RE: [PATCH kernel v5 5/5] virtio-balloon: tell host vm's unused  page info "Li, Liang Z" <liang.z.li@intel.com> - 2016-12-06 05:50 +0100
  [PATCH kernel v5 2/5] virtio-balloon: define new feature bit and head struct Liang Li <liang.z.li@intel.com> - 2016-11-30 10:00 +0100
  [PATCH kernel v5 4/5] virtio-balloon: define flags and head for host request vq Liang Li <liang.z.li@intel.com> - 2016-11-30 10:00 +0100
  [PATCH kernel v5 1/5] virtio-balloon: rework deflate to add page to a list Liang Li <liang.z.li@intel.com> - 2016-11-30 10:00 +0100
  Re: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration David Hildenbrand <david@redhat.com> - 2016-12-06 09:50 +0100
    RE: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-12-07 14:40 +0100
      Re: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-12-07 16:40 +0100
        RE: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-12-09 04:10 +0100
      Re: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-12-07 16:50 +0100
        Re: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration David Hildenbrand <david@redhat.com> - 2016-12-07 17:30 +0100
          Re: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-12-07 18:00 +0100
            Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for  fast (de)inflating & fast live migration Andrea Arcangeli <aarcange@redhat.com> - 2016-12-07 19:40 +0100
              Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-12-07 20:00 +0100
                Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for  fast (de)inflating & fast live migration Andrea Arcangeli <aarcange@redhat.com> - 2016-12-07 20:00 +0100
              Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-12-07 21:00 +0100
                Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for  fast (de)inflating & fast live migration Andrea Arcangeli <aarcange@redhat.com> - 2016-12-07 21:30 +0100
                RE: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for  fast (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-12-09 05:50 +0100
                Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration Dave Hansen <dave.hansen@intel.com> - 2016-12-09 06:00 +0100
                RE: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for  fast (de)inflating & fast live migration "Li, Liang Z" <liang.z.li@intel.com> - 2016-12-09 06:40 +0100
                Re: [Qemu-devel] [PATCH kernel v5 0/5] Extend virtio-balloon for  fast (de)inflating & fast live migration Andrea Arcangeli <aarcange@redhat.com> - 2016-12-09 17:50 +0100
      Re: [PATCH kernel v5 0/5] Extend virtio-balloon for fast  (de)inflating & fast live migration David Hildenbrand <david@redhat.com> - 2016-12-07 16:50 +0100

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