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Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1G
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6) |
Date: |
Wed, 11 Dec 2013 15:45:29 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130923 Thunderbird/17.0.9 |
Il 11/12/2013 15:20, Michael S. Tsirkin ha scritto:
> > It means that its necessary to expose that 3-4GB physical memory region
> > in QEMU belongs to the same node (that is, guest must be aware that
> > 3-3.75GB and the tail of RAM are on the same node).
> >
> > So the problem Paolo mentions is fixable.
I'm not sure if it is fixable. You need a 2M mountpoint to bind the 3G-4G
range correctly, a 1G mountpoint for everything else, and QEMU only allows
to specify one path.
Without Marcelo's patch there is a workaround; if you know the size of the 4G
hole and configure the first two nodes with unequal sizes. For example
-m 8192 \
-object memory-ram,id=ram-node0,size=3840M,hostnode=0 -numa
node,memdev=ram-node0 \
-object memory-ram,id=ram-node1,size=4352M,hostnode=1 -numa
node,memdev=ram-node1
RAM address Host virtual address low bits Guest physical
addresses
0M-3840M 0 0M-3840M
3840M-8192M 0 4096M-8448M
Then you'll waste 1GB of RAM (you'll use 9 hugepages instead of 8), but
everything will be aligned. Or you just make your guest 7680M and not waste
the memory.
But with Marcelo's patch, ram-node1 will be split in two. QEMU will try
to realign the second part of ram-node1, but the result is that the second
part is misaligned and only the first 256M (the tail of guest physical
memory) stays aligned:
RAM address Host virtual address low bits Guest physical
addresses
0M-3840M 0 0M-3840M
4096M-8192M 256M 4096M-8192M
3840M-4096M 0 8192M-8448M
So you still waste memory, _and_ get incorrect alignment.
> Okay so
> Marcelo - do you ack this patch for 2.0?
> Paolo - do you re-ack this patch for 2.0?
I very much prefer Gerd's approach. 2GB low memory for q35 is a bit wasteful,
but we have some time to fix that before release.
Paolo
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), (continued)
Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Michael S. Tsirkin, 2013/12/10
Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Marcelo Tosatti, 2013/12/10
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Marcelo Tosatti, 2013/12/10
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Michael S. Tsirkin, 2013/12/10
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Marcelo Tosatti, 2013/12/11
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Michael S. Tsirkin, 2013/12/11
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6),
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Michael S. Tsirkin, 2013/12/11
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Paolo Bonzini, 2013/12/11
- Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Michael S. Tsirkin, 2013/12/11
Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Igor Mammedov, 2013/12/11
Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Paolo Bonzini, 2013/12/11
Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6), Marcelo Tosatti, 2013/12/11