Re: how does mmap() work? (also teraspace and user spaces)

["Larry Loen" <lwloen@xxxxxxxxxx>]

Steve Richter asked:

   hola,

   What I think I  know:

   The mmap( ) function is used to map a stream  file into memory.

   The func rcvs an offset into the file and the  length of bytes to be
   mapped. It returns a ptr to the start of the mapped  memory.
       char*  pData ;
        dword nNbrBytesToMap = 17Meg ;
        pData = mmap( NULL, nNbrBytesToMap, , , FileHandle, OfsIntoFile ) ;

   The ptr can then be used to write to the stream  file:
       pData[17,000,000] = 'x'  ;  /* copies 'x' to offset 17 million into
   the stream file */
   Multiple jobs can map the same stream file at the same time.  The end
   result being a perm shared space that exceeds the 16 mem space size
   limit.

   My questions:
   How is mapped memory implemented?
   What chgs to the architecture, virtual memory  manager were needed to be
   able to do this?
   Are teraspaces implemented the same way?


   Just asking,

   Steve Richter


Try the following link:
http://www-1.ibm.com/servers/eserver/iseries/beyondtech/unix.htm  (titled:
A Unix-like environment)

and the follow-on link:
http://www-1.ibm.com/servers/eserver/iseries/beyondtech/teraspace.htm
(titled:  Teraspace storage)

which ought to answer many of the issues of the last couple of days.  I
found these via Google.





Larry W. Loen  -   Senior Java and iSeries Performance Analyst
                          Dept HP4, Rochester MN

speaking on his own

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