On 06/03/2014 11:46 PM, Ralf Baechle wrote:
A more important value which I haven't noticed the Looongson patches to
modify is SECTION_SIZE_BITS in <asm/sparsemem.h>:
#if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT) && defined(CONFIG_PAGE_SIZE_64KB)
# define SECTION_SIZE_BITS 29
#else
# define SECTION_SIZE_BITS 28
#endif
Don't ask me why its definition depends on MIPS_HUGE_TLB_SUPPORT and
PAGE_SIZE_64KB - the value describes the larges chunk of contiguous
memory (that is for example memory per node) and that doesn't depend
on these CONFIG_* symbols.
I think I can answer that. We do the same thing for OCTEON I think.
IIRC, with SPARSEMEM, you cannot allocate high order pages that span
multiple sections. Therefore you have to have the sections be at least
as large as a huge page. in the case of CONFIG_PAGE_SIZE_64KB, the huge
pages are 512MB which doesn't fit in 28 bits.
David.
Ralf
