Hello, On Thu, Dec 01, 2011 at 11:57:18AM +0100, Uwe Kleine-König wrote: > On Tue, Nov 29, 2011 at 10:39:10PM -0200, Fabio Estevam wrote: > > 2011/11/29 Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>: > > > Hello, > > > > > > I'm currently working on a new arch port and my current machine has RAM > > > at 0x10000000 and 0x80000000. So there is a big hole between the two > > > banks. When selecting the sparse memory model it works, but when > > > selecting flat the machine runs into a BUG in mark_bootmem() called by > > > free_unused_memmap() to free the space between the two banks. > > > > My understanding is that you have to select ARCH_HAS_HOLES_MEMORYMODEL. > I think that is not necessary. > > > > Is that expected (meaning I cannot use the flat model)? I currently > > > don't have another machine handy that has >1 memory back to test that. > > > > In case you have access to a MX35PDK you can try on this board as it does have > > the memory hole. > No I havn't, but I just used a 128MB machine and changed that in the > .fixup callback to 64MB + 32MB with a 32MB hole in between and it works > fine without ARCH_HAS_HOLES_MEMORYMODEL. > > I debugged the problem a bit further and one symptom is that > > struct page *mem_map > > is NULL for me. That looks wrong. I guess this is just broken for nommu. > I will dig into that later today. The problem is that the memory for mem_map is allocated using: map = alloc_bootmem_node_nopanic(pgdat, size); without any error checking. The _nopanic was introduced by commit 8f389a99 (mm: use alloc_bootmem_node_nopanic() on really needed path) I don't understand the commit's log and don't really see why it should be allowed to not panic if the allocation failes here but use a NULL pointer instead. I put the people involved in 8f389a99 on Cc, maybe someone can comment? Apart from that it seems I cannot use flatmem as is on my machine. It has only 128kiB@0x10000000 + 1MiB@0x80000000 and needs 14MiB to hold the table of "struct page"s. :-( Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>