Messages in this thread | | | Date | Sat, 19 Aug 2006 03:19:16 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [MODSLAB 3/7] A Kmalloc subsystem |
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On Fri, 18 Aug 2006 09:58:13 -0700 (PDT) Christoph Lameter <clameter@sgi.com> wrote:
> On Fri, 18 Aug 2006, KAMEZAWA Hiroyuki wrote: > > > Just a note: with SPARSEMEM, we need more calculation and access to > > mem_section[] table and page structs(mem_map). > > Uhh, a regression against DISCONTIG. Could you address that issue? > At first, ia64's DISCONTIG is special because of VIRTUAL_MEMMAP. and ia64's SPARSEMEM is special,too. it's SPARSEMEM_EXTREME.
Considering generic arch, see include/asm-generic/memory_model.h, which doesn't use virtual mem_map.
with FLATMEM, pfn_to_page() is pfn + mem_map. just an address calclation.
with *usual* DISCONTIG -- pgdat = NODE_DATA(pfn_to_nid(pfn)); page = pgdat->node_mem_map + pfn - pgdat->node_start_pfn -- if accessing to pgdat is fast, cost will not be big problem. pfn_to_nid() is usually implemeted by calclation or table look up.
and usual SPARSEMEM, (not EXTREME) -- page = mem_section[(pfn >> SECTION_SHIFT)].mem_map + pfn -- need one table look up. maybe not very big.
with SPARSEMEM_EXTREME -- page = mem_section[(pfn >> SECTION_SHIFT)][(pfn & MASK)].mem_map + pfn -- need one (big)table look up.
-Kame
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