Am 01.12.2011 16:39, schrieb Uwe Kleine-König: > 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 > The commit was made after an bug report from me. I have an old x86 tablet pc with only 8Mb Ram. This machine fails early on bootup without this commit. I found an archived message of the bug report here: http://comments.gmane.org/gmane.linux.kernel/1135909 Regards, Stefan -- 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>