pfn_valid() more generic : intro[0/2]

Hi,

ia64's ia64_pfn_valid() uses get_user() for checking whether a page struct is available or not. I think this is an irregular implementation and following patches are a more generic replacement, careful_pfn_valid(). It uses 2 level table.

Core Algorithm
====
1st level, pfn_validmap[] has index to 2nd level table. 2nd level table is consists of (start, end) entries of valid pfns.

careful_pfn_valid(pfn)
-> pfn_validmap[(pfn >> PFN_VALID_MAPSHIFT)] == entry

     if (entry ==  ALL_VALID) return 1
     if (entry ==  ALL_INVALID)  return 0

      -> check 2nd level,
     info = pfn_valid_info_table + entry.
     while(info->start_pfn < pfn) {
          if((info->start_pfn <= pfn) && (info->end_pfn > pfn))
                     return 0;
               info++;
     }
     return 1;

====
sizeof(entry) is 2 bytes and each entry covers 1GB with current config(16k pages).

Here is kernbench results on my Tiger4 (Itanium2(1.3GHz) x2, 8 Gbytes memory),pagesize=16k

Average Optimal -j8 Load Run:
Elapsed Time User Time System Time Percent CPU C/Switch Sleeps

2.6.9-rc3                 699.906       1322.01     39.336        194        64390    74416.8
2.6.9-rc3 + this_patch    698.478       1321.76     38.228        194        64502    74185

there are no difference :)

For NUMA, I think tables for careful_pfn_valid() should be copied to each node's local memory, but I haven't implemented it yet.

-- Kame <[email protected]>

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