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Re: [Qemu-devel] Re: [PATCH 1/6] Use correct types to enable > 2G suppor

From: Robert William Fuller
Subject: Re: [Qemu-devel] Re: [PATCH 1/6] Use correct types to enable > 2G support
Date: Fri, 01 Feb 2008 06:56:11 -0500
User-agent: Thunderbird (X11/20071013)

Avi Kivity wrote:
Anthony Liguori wrote:
Fabrice Bellard wrote:
Anthony Liguori wrote:
+    /* above 4giga memory allocation */
+    if (above_4g_mem_size > 0) {
+        ram_addr = qemu_ram_alloc(above_4g_mem_size);
+ cpu_register_physical_memory(0x100000000, above_4g_mem_size, ram_addr);
+    }

Why do you need this ? All the RAM can be registered with a single call. I fear you need to do that because of KVM RAM handling limitations.

On the x86, there is a rather large hole at the top of memory. Currently, we do separate allocations around this whole. You can't get away from doing multiple cpu_register_physical_memory calls here. We've discussed just allocating a single chunk with qemu_ram_alloc since so many places in QEMU assume that you can do phys_ram_base + PA.

I think I'll change this too into a single qemu_ram_alloc. That will fix the bug with KVM when using -kernel and large memory anyway :-)

Won't that cause all of the memory in the hole to be wasted?

You could munmap() it, but it's hardly elegant.

Linux doesn't commit mapped memory until it's faulted. As for other platforms, who knows?

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