Re: [PATCH v2 2/4] powerpc/64/mm: implement page mapping percpu first chunk allocator

"Aneesh Kumar K.V" [off-list ref] writes:

Implement page mapping percpu first chunk allocator as a fallback to
the embedding allocator. With 4K hash translation we limit our page
table range to 64TB and commit: 0034d395f89d ("powerpc/mm/hash64: Map all the
kernel regions in the same 0xc range") moved all kernel mapping to
that 64TB range. In-order to support sparse memory layout we need
to increase our linear mapping space and reduce other mappings.

With such a layout percpu embedded first chunk allocator will fail
because of small vmalloc range. Add a fallback to page mapping
percpu first chunk allocator for such failures.

The below dmesg output can be observed in such case.

 percpu: max_distance=0x1ffffef00000 too large for vmalloc space 0x10000000000
 PERCPU: auto allocator failed (-22), falling back to page size
 percpu: 40 4K pages/cpu s148816 r0 d15024

This patch requires powersave=off kernel command line to boot. We are
working to make sure we don't access per cpu variables in real mode.
Additionally, you can also try the below workaround patch

modified   arch/powerpc/kernel/mce.c

@@ -711,7 +711,7 @@ long hmi_exception_realmode(struct pt_regs *regs)
 {	
 	int ret;
 
-	__this_cpu_inc(irq_stat.hmi_exceptions);
+//	__this_cpu_inc(irq_stat.hmi_exceptions);
 
 	ret = hmi_handle_debugtrig(regs);
 	if (ret >= 0)


-aneesh