On Fri, Jul 30, 2010 at 5:55 AM, Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> wrote: > On Thu, 2010-07-29 at 19:33 +0100, Russell King - ARM Linux wrote: >> And no, setting the sparse section size to 512kB doesn't work - memory is >> offset by 256MB already, so you need a sparsemem section array of 1024 >> entries just to cover that - with the full 256MB populated, that's 512 >> unused entries followed by 512 used entries. That too is going to waste >> memory like nobodies business. > > Sparsemem could use some work in the case where memory doesn't start at > 0x0. But, it doesn't seem like it would be _too_ oppressive to add. > It's literally just adding an offset to all of the places where a > physical address is stuck into the system. It'll make a few of the > calculations longer, of course, but it should be manageable. > > Could you give some full examples of how the memory is laid out on these > systems? I'm having a bit of a hard time visualizing it. > > As Christoph mentioned, SPARSEMEM_EXTREME might be viable here, too. > > If you free up parts of the mem_map[] array, how does the buddy > allocator still work? I thought we required at 'struct page's to be > contiguous and present for at least 2^MAX_ORDER-1 pages in one go. I think in that case, arch should define CONFIG_HOLES_IN_ZONE to prevent crash. But I am not sure hole architectures on ARM have been used it well. Kujkin's problem happens not buddy but walking whole pfn to echo min_free_kbytes. > > -- Dave > > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href