On 28.02.2012 [14:53:26 +0100], Johannes Weiner wrote: > On Fri, Feb 24, 2012 at 11:33:58AM -0800, Nishanth Aravamudan wrote: > > While testing AMS (Active Memory Sharing) / CMO (Cooperative Memory > > Overcommit) on powerpc, we tripped the following: > > > > kernel BUG at mm/bootmem.c:483! > > cpu 0x0: Vector: 700 (Program Check) at [c000000000c03940] > > pc: c000000000a62bd8: .alloc_bootmem_core+0x90/0x39c > > lr: c000000000a64bcc: .sparse_early_usemaps_alloc_node+0x84/0x29c > > sp: c000000000c03bc0 > > msr: 8000000000021032 > > current = 0xc000000000b0cce0 > > paca = 0xc000000001d80000 > > pid = 0, comm = swapper > > kernel BUG at mm/bootmem.c:483! > > enter ? for help > > [c000000000c03c80] c000000000a64bcc > > .sparse_early_usemaps_alloc_node+0x84/0x29c > > [c000000000c03d50] c000000000a64f10 .sparse_init+0x12c/0x28c > > [c000000000c03e20] c000000000a474f4 .setup_arch+0x20c/0x294 > > [c000000000c03ee0] c000000000a4079c .start_kernel+0xb4/0x460 > > [c000000000c03f90] c000000000009670 .start_here_common+0x1c/0x2c > > > > This is > > > > BUG_ON(limit && goal + size > limit); > > > > and after some debugging, it seems that > > > > goal = 0x7ffff000000 > > limit = 0x80000000000 > > > > and sparse_early_usemaps_alloc_node -> > > sparse_early_usemaps_alloc_pgdat_section -> alloc_bootmem_section calls > > > > return alloc_bootmem_section(usemap_size() * count, section_nr); > > > > This is on a system with 8TB available via the AMS pool, and as a quirk > > of AMS in firmware, all of that memory shows up in node 0. So, we end up > > with an allocation that will fail the goal/limit constraints. In theory, > > we could "fall-back" to alloc_bootmem_node() in > > sparse_early_usemaps_alloc_node(), but since we actually have HOTREMOVE > > defined, we'll BUG_ON() instead. A simple solution appears to be to > > disable the limit check if the size of the allocation in > > alloc_bootmem_secition exceeds the section size. > > It makes sense to allow the usemaps to spill over to subsequent > sections instead of panicking, so FWIW: > > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> > > That being said, it would be good if check_usemap_section_nr() printed > the cross-dependencies between pgdats and sections when the usemaps of > a node spilled over to other sections than the ones holding the pgdat. > > How about this? > > --- > From: Johannes Weiner <hannes@xxxxxxxxxxx> > Subject: sparsemem/bootmem: catch greater than section size allocations fix > > If alloc_bootmem_section() no longer guarantees section-locality, we > need check_usemap_section_nr() to print possible cross-dependencies > between node descriptors and the usemaps allocated through it. > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > --- > > diff --git a/mm/sparse.c b/mm/sparse.c > index 61d7cde..9e032dc 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -359,6 +359,7 @@ static void __init sparse_early_usemaps_alloc_node(unsigned long**usemap_map, > continue; > usemap_map[pnum] = usemap; > usemap += size; > + check_usemap_section_nr(nodeid, usemap_map[pnum]); > } > return; > } This makes sense to me -- ok if I fold it into the re-worked patch (based upon Mel's comments)? > --- > > Furthermore, I wonder if we can remove the sparse-specific stuff from > bootmem.c as well, as now even more so than before, calculating the > desired area is really none of bootmem's business. > > Would something like this be okay? > > --- > From: Johannes Weiner <hannes@xxxxxxxxxxx> > Subject: [patch] mm: remove sparsemem allocation details from the bootmem allocator > > alloc_bootmem_section() derives allocation area constraints from the > specified sparsemem section. This is a bit specific for a generic > memory allocator like bootmem, though, so move it over to sparsemem. > > Since __alloc_bootmem_node() already retries failed allocations with > relaxed area constraints, the fallback code in sparsemem.c can be > removed and the code becomes a bit more compact overall. > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> I've not tested it, but the intention seems sensible. I think it should remain a separate change. Thanks, Nish -- Nishanth Aravamudan <nacc@xxxxxxxxxx> IBM Linux Technology Center -- 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>