Re: [patch 0/4] ia64 SPARSEMEM

David Mosberger
2005-05-27T16:23:24Z

>>>>> On Fri, 27 May 2005 06:35:48 -0400, Bob Picco <bob.picco@hp.com> said:

Bob> luck wrote: [Thu May 26 2005, 06:03:29PM EDT]
>> >Well worse case it would consume 2^(1(50-32)+3) (2 Mb). I would hope that
>> >it's not configured for 28 SECTION_SIZE_BITS and 50 physical. This would
>> >be excessive 2^((50-28)+3 = 32Mb and not advised.

>> While you can tune a custom kernel for a particular system configuration,
>> we might have to use the 50/28 configuration for the generic "defconfig"
>> case ... that kernel should be bootable anywhere. SGI needs (or will
>> need) the "50" for total physical size, and other platforms may need the
>> "28" (is that even small enough? We currently have "granule" sizes of
>> 16M and 64M to cope with odd holes in the physical address space ... so
>> perhaps the section size might need to be even smaller: 24 or 26? How did
>> you come up with 28 as the low bound for SECTION_BITS?)

Bob> It seems to be least costly in terms of consuming reserved
Bob> pages. Of course reducing it decreases consuming reserved pages
Bob> but at the cost of increasing the mem_section size. Should 50
Bob> have to be the defconfig value, then I'd recommend 30 for
Bob> SECTION_SIZE_BITS. So memory wise 8Mb -> 2^((50-30)+3) for
Bob> mem_section. Smaller than 30 SECTION_BITS for 50 bit physical
Bob> consumes too much memory for mem_section.

This discussion just demonstrates what a pain such config parameters
are. Such stuff need to be
self-adjusting/self-tuning/able-to-cover-any-configuration. Virtual
mem-map seems to qualify much better here.

--david