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Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing
From: |
Paul Brook |
Subject: |
Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away |
Date: |
Mon, 22 Jun 2009 20:38:00 +0100 |
User-agent: |
KMail/1.11.4 (Linux/2.6.29-2-amd64; KDE/4.2.4; x86_64; ; ) |
> >>> We have the same issue on the migration source node. I don't see a
> >>> simple way to solve it, though.
> >>
> >> I don't follow. In this case, the issue is:
> >>
> >> 1) Start a guest with 1024, balloon down to 128MB. RSS size is now
> >> ~128MB
> >> 2) Live migrate to a different node
> >> 3) RSS on different node jumps to ~1GB
> >
> > 3.5) RSS on source node jumps to ~1GB, since reading the page
> > instantiates the pte
>
> Surely we can do better here...
Huh, I'm surprised we have to. I was expecting linux to populate the region
with CoW mappings of a single zero page, but apparently not. I guess reading a
zero page without writing to it is a fairly rare case, and it's usually better
to instantiate a writable page on the first access.
Paul
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, (continued)
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Anthony Liguori, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Avi Kivity, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Anthony Liguori, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Avi Kivity, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Anthony Liguori, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Avi Kivity, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Anthony Liguori, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Avi Kivity, 2009/06/22
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away,
Paul Brook <=
- Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away, Anthony Liguori, 2009/06/22