On Tuesday 06 February 2007 10:53, Jan Beulich wrote: > >> I don't think I remember a restriction here, at least not below 44 bits > >> (that's where pfn-s would need to become 64-bit wide). > > > >The i386 mm code only supports 4 entries in the PGD, so more than 36bit > >cannot > >be mapped right now. > > That has nothing to do with the number of physical address bits.
You couldn't use the memory in any ways. Anyways I give up -- the check is probably not needed, unless Andreas comes up with a good reason. > > >Also even 64MB barely works (many boxes don't boot), you would likely > >need at least the 4:4 patch to go >64GB. Also we know there are tons > >of possible deadlocks in various subsystems when the lowmem:highmem ratio > >gets so out of hand. > > > >Ok it could be probably all fixed with some work (at least the mm part, > >the deadlocks would be more tricky), but would seem fairly > >pointless to me because all machines with >36bits support are 64bit capable. > > That's a different story, and certainly a limiting factor. But this shouldn't > e.g. disallow (hypothetical?) systems that have a very sparse memory map > extending beyond 64G. They would need a discontig kernel to boot most likely, otherwise mem_map would fill up their memory. And I was told Windows doesn't like that, so it's unlikely there will ever be such x86 machines. -Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/