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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] Re: [Qemu-commits] [COMMIT 3086844] Instead of writing a zero page, madvise it away |
Date: | Mon, 22 Jun 2009 14:49:45 -0500 |
User-agent: | Thunderbird 2.0.0.21 (X11/20090320) |
Paul Brook wrote:
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 ~1GB3.5) RSS on source node jumps to ~1GB, since reading the page instantiates the pteSurely 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.
I did too. If you mmap(/dev/zero) you'll get that behavior but not with a normal allocation.
Regards, Anthony Liguori
Paul
-- Regards, Anthony Liguori
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