On Wed, Feb 29, 2012 at 10:12:33AM -0800, Nishanth Aravamudan wrote: > On 28.02.2012 [15:47:32 +0000], Mel Gorman 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. > > > > > > Signed-off-by: Nishanth Aravamudan <nacc@xxxxxxxxxx> > > > Cc: Dave Hansen <haveblue@xxxxxxxxxx> > > > Cc: Anton Blanchard <anton@xxxxxxxxxxx> > > > Cc: Paul Mackerras <paulus@xxxxxxxxx> > > > Cc: Ben Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> > > > Cc: Robert Jennings <rcj@xxxxxxxxxxxxxxxxxx> > > > Cc: linux-mm@xxxxxxxxx > > > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx > > > --- > > > include/linux/mmzone.h | 2 ++ > > > mm/bootmem.c | 5 ++++- > > > 2 files changed, 6 insertions(+), 1 deletions(-) > > > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > > index 650ba2f..4176834 100644 > > > --- a/include/linux/mmzone.h > > > +++ b/include/linux/mmzone.h > > > @@ -967,6 +967,8 @@ static inline unsigned long early_pfn_to_nid(unsigned long pfn) > > > * PA_SECTION_SHIFT physical address to/from section number > > > * PFN_SECTION_SHIFT pfn to/from section number > > > */ > > > +#define BYTES_PER_SECTION (1UL << SECTION_SIZE_BITS) > > > + > > > #define SECTIONS_SHIFT (MAX_PHYSMEM_BITS - SECTION_SIZE_BITS) > > > > > > #define PA_SECTION_SHIFT (SECTION_SIZE_BITS) > > > diff --git a/mm/bootmem.c b/mm/bootmem.c > > > index 668e94d..5cbbc76 100644 > > > --- a/mm/bootmem.c > > > +++ b/mm/bootmem.c > > > @@ -770,7 +770,10 @@ void * __init alloc_bootmem_section(unsigned long size, > > > > > > pfn = section_nr_to_pfn(section_nr); > > > goal = pfn << PAGE_SHIFT; > > > - limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT; > > > + if (size > BYTES_PER_SECTION) > > > + limit = 0; > > > + else > > > + limit = section_nr_to_pfn(section_nr + 1) << PAGE_SHIFT; > > > > As it's ok to spill the allocation over to an adjacent section, why not > > just make limit==0 unconditionally. That would avoid defining > > BYTES_PER_SECTION. > > Something like this? > > Andrew, presuming Mel & Johannes give their, ack this should presumably > supersede the patch you pulled into -mm. > > Thanks, > Nish > > ------- > > 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 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 > unconditionally remove the limit condition in alloc_bootmem_section, > meaning allocations are allowed to cross section boundaries (necessary > for systems of this size). > > Johannes Weiner pointed out that 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. That makes the two loops in > sparse_early_usemaps_alloc_node() identical, so re-factor the code a > bit. > > Signed-off-by: Nishanth Aravamudan <nacc@xxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> -- 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>