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Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1G
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH rebased for-1.8] i386: pc: align gpa<->hpa on 1GB boundary (v6) |
Date: |
Wed, 11 Dec 2013 16:45:29 +0100 |
On Wed, 11 Dec 2013 15:45:29 +0100
Paolo Bonzini <address@hidden> wrote:
> 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.
we could do it with hugepage memdev backend.
something like:
-object hugepage-ram,id=mem1gb,size=3G,host-node=0,mem-path=/1gb-hugepage-fs
-device dimm,id=hp1g,memdev=mem1gb,node=0
-object hugepage-ram,id=mem2mb,size=500Mb,host-node=1,mem-path=/2mb-hugepage-fs
-device dimm,id=hp2mb,memdev=mem2mb,node=1
that basically would allow to distribute initial memory in any way user would
like.
>
> 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
>
--
Regards,
Igor
- 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, 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, 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 <=
- 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