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On Sat, Jan 26, 2002 at 01:20:45AM +0100, Benjamin Herrenschmidt wrote: > > > >Looking at bat_mapin_ram, it looks like we only map the first 512MB of > >RAM with BATs, so we actually map the 512MB - 768MB range with PTEs > >(and highmem starts at 768MB). Two of the DBATs are used by I/O > >mappings, so that only leaves two DBATs of 256MB each to map lowmem > >anyway. Am I missing something? > > No, except maybe my last patch that actually limits lowmem to 512Mb ;) :) > I don't think we use the io mapping BATs any more, do we ? (well, > maybe on PReP...) I don't on pmac. Lots and lots of PPC platforms use BATs for io mappings: val@evilcat </sys/linuxppc_2_4_devel_pristine/arch/ppc/platforms>$ grep -l ppc_md.setup_io_mappings * grep: SCCS: Is a directory adir_setup.c apus_setup.c chrp_setup.c gemini_setup.c k2_setup.c lopec_setup.c mcpn765_setup.c menf1_setup.c mvme5100_setup.c pcore_setup.c powerpmc250.c pplus_setup.c prep_setup.c prpmc750_setup.c prpmc800_setup.c sandpoint_setup.c spruce_setup.c zx4500_setup.c I'm trying to get highmem working on Gemini, hence my interest. > >By the way, does the "nobats" option currently work on PowerMac? > > No, nor on any other BAT-capable PPC (and that's the reason why I > did the above). Basically, our exception return path and some of > the hash manipulation functions aren't safe without BAT mapping, > especially on SMP when you can get evicted from the hash table > by the other CPU in places where taking hash faults isn't safe. Hm, that's what I thought. Thanks for confirming that. -VAL - 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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