Messages in this thread | | | Date | Fri, 16 Apr 2004 10:07:44 -0700 | From | Ross Biro <> | Subject | Re: Kernel writes to RAM it doesn't own on 2.4.24 |
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On Fri, 16 Apr 2004 12:55:33 -0400 (EDT), Richard B. Johnson <root@chaos.analogic.com> wrote: > > On Fri, 16 Apr 2004, Ross Biro wrote: > > > mem= isn't there to tell the kernel what ram it owns and what ram it > > doesn't own. It's there to tell the kernel what ram is in the system. > > Since you told the system it only has 500m, it assumes the rest of > > the 3.5G of address space is available for things like memory mapped > > i/o. If you cat /proc/iomem, you'll probably see something has > > reserved the memory range in question. > > > > No! This is address space, not RAM. Whether or not a PCI device > or whatever has internal RAM that's mapped makes no difference. > > I told the kernel that it has 500m of RAM. It better not assume > I don't know what I'm talking about. I might have reserved that > RAM because it's bad or I may have something else important to > do with that RAM (which I do).
The problem is that the kernel does assume you know what you are talking about, and you don't. You are abusing the mem= parameter. That's fine, but then you have to tell the kernel what you really mean. What you really want to say is there is memory above 500M and I don't want you to touch it. There may be a way to do that via the fancy mem=@ parameters.
What mem= tells the kernel is that there is RAM in a certain spot an no where else. Since you told the kernel there is no ram about 500M, that means that address space is free to be used for memory mapped I/O. Since the kernel trusts you, it started using the memory above 500m for memory mapped i/o. Since you LIED to the kernel, you are getting results you do not like. The solution I settled on was to tell the kernel that people LIE to it and only use memory for I/O if both the BIOS and the USER agree that it's available. You have to find a way to tell the kernel the TRUTH, or you will never get the results you want. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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