Re: powerpc/mm: Update the FORCE_MAX_ZONEORDER range to enable hugetlb

On Mon, 2016-19-09 at 17:31:33 UTC, "Aneesh Kumar K.V" wrote:

For hugetlb to work with 4K page size, we need the MAX_ORDER to be more
than 13. When switching from a 64K page size to 4K linux page size using
make nconfig, we endup with a CONFIG_FORCE_MAX_ZONEORDER value of 9.
This results in 16M hugepage to be considered as a gigantic huge page
which inturn can result in failure to setup hugepages if gigantic
hugepage support is not enabled.

This also results in kernel crash with 4K radix configuration. We
hit the below BUG_ON on radix

 kernel BUG at mm/huge_memory.c:364!
 Oops: Exception in kernel mode, sig: 5 [#1]
 SMP NR_CPUS=2048 NUMA PowerNV
 Modules linked in:
 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.8.0-rc1-00006-gbae9cc6 #1
 task: c0000000f1af8000 task.stack: c0000000f1aec000
 NIP: c000000000c5fa0c LR: c000000000c5f9d8 CTR: c000000000c5f9a4
 REGS: c0000000f1aef920 TRAP: 0700   Not tainted (4.8.0-rc1-00006-gbae9cc6)
 MSR: 9000000102029033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE,TM[E]>  CR: 24000844  XER: 00000000
 CFAR: c000000000c5f9e0 SOFTE: 1
.....
 NIP [c000000000c5fa0c] hugepage_init+0x68/0x238
 LR [c000000000c5f9d8] hugepage_init+0x34/0x238

Fixes: a7ee539584acf ("powerpc/Kconfig: Update config option based on page size")

Reported-by: Santhosh <redacted>
Signed-off-by: Aneesh Kumar K.V <redacted>
Acked-by: Balbir Singh <bsingharora@gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/d5a1e42cb4be016a45a787953d

cheers