Messages in this thread |  | | Date | Wed, 04 Sep 2002 08:32:15 -0700 | From | "Martin J. Bligh" <> | Subject | Re: consequences of lowering "MAX_LOW_MEM"? |
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>> In 2.4.x (currently using 2.4.18), for PPC, there is a value for >> "MAX_LOW_MEM" defined in "arch/ppc/mm/pgtable.c" as 768MB RAM. Any >> memory above 768MB is considered "high" memory. Now our problem is >> that we have 1024MB of onboard RAM on our card. I do *NOT* wish to >> compile with "CONFIG_HIGHMEM" set to true (see below for why), but i >> do wish to have full use of the 1024MB of RAM onboard, or at least >> 992MB which is the minimum for our app. >> So what I did was just change "MAX_LOW_MEM" to be 0x3E000000 >> (0x30000000), ie. change it to 992 from 768. I recompiled and tested >> our application. Things seemed to be running normal with a max of >> 992MB of RAM. >> >> Is this a potential problem, or will this cause some lurking bug that >> anyone can think of? (ie. I'm sure "MAX_LOW_MEM" was set to 768MB for >> a reason, but what is that reason). We don't want to move higher >> than 1Gig RAM for now, so are we going to be okay doing what I >> describe above? Any suggestions or comments as to why that's a very >> bad idea would be greatly appreciated. Again, this is for a >> PPC-specific board, I'm not sure what the x86 architecture's low >> memory max is.
I think you'll find yourself with no virtual address space left to do vmalloc / fixmap / kmap type stuff. Or at least you would on i386, I presume it's the same for ppc. Sounds like you may have left yourself enough space for fixmap & kmap, but any calls to vmalloc will probably fail ?
M.
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