On Wed, Jan 04, 2017 at 01:50:20PM +0000, Ard Biesheuvel wrote: > On 4 January 2017 at 13:28, Will Deacon <will.deacon@xxxxxxx> wrote: > > On Wed, Dec 14, 2016 at 09:11:47AM +0000, Ard Biesheuvel wrote: > >> The NUMA code may get confused by the presence of NOMAP regions within > >> zones, resulting in spurious BUG() checks where the node id deviates > >> from the containing zone's node id. > >> > >> Since the kernel has no business reasoning about node ids of pages it > >> does not own in the first place, enable CONFIG_HOLES_IN_ZONE to ensure > >> that such pages are disregarded. > >> > >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > >> --- > >> arch/arm64/Kconfig | 4 ++++ > >> 1 file changed, 4 insertions(+) > >> > >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > >> index 111742126897..0472afe64d55 100644 > >> --- a/arch/arm64/Kconfig > >> +++ b/arch/arm64/Kconfig > >> @@ -614,6 +614,10 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK > >> def_bool y > >> depends on NUMA > >> > >> +config HOLES_IN_ZONE > >> + def_bool y > >> + depends on NUMA > >> + > >> source kernel/Kconfig.preempt > >> source kernel/Kconfig.hz > > > > I'm happy to apply this, but I'll hold off until the first patch is queued > > somewhere, since this doesn't help without the VM_BUG_ON being moved. > > > > Alternatively, I can queue both if somebody from the mm camp acks the > > first patch. > > > > Actually, I am not convinced the discussion is finalized. These > patches do fix the issue, but Robert also suggested an alternative fix > which may be preferable. > > http://marc.info/?l=linux-arm-kernel&m=148190753510107&w=2 > > I haven't responded to it yet, due to the holidays, but I'd like to > explore that solution a bit further before applying anything, if you > don't mind. Using early_pfn_valid feels like a bodge to me, since having pfn_valid return false for something that early_pfn_valid says is valid (and is therefore initialised in the memmap) makes the NOMAP semantics even more confusing. But there's no rush, so I'll hold off for the moment. I was under the impression that things had stalled. Will -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>