Date: Thu, 14 Sep 2006 09:55:09 +0100 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: RJ45 <rj45@slacknet.com> Cc: freebsd-questions@freebsd.org Subject: Re: memory problem Message-ID: <450918ED.6030206@infracaninophile.co.uk> In-Reply-To: <Pine.LNX.4.61.0609140220420.18820@slacknet.com> References: <Pine.LNX.4.61.0609140220420.18820@slacknet.com>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig9DC83E041CB514700A69BA14 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: quoted-printable RJ45 wrote: > THe system has exactly 4GB of memory but the memory is not complitely > seen by the system. >=20 > At boot thime I Get this warning >=20 > 524288Kb of memory above 4GB ignored A normal 32bit OS can only address 4GB RAM -- but your system has various= L2 and other caches built into the CPUs, etc., which count towards the to= tal RAM count. So the excess is trimmed from the main memory. If you need to use more than 4GB RAM then either switch to a 64Bit OS, or= =20 investigate 'PAE'. You can run the 64bit version of FreeBSD on Intel Xeons (so long as they support EMT64) or the various AMD 64 bit processors. Xeons don't have as= complete 64-bitness as Opterons so performance may not be as good as runn= ing 32bit. Mind you that sort of thing depends heavily on the particular workload and you should benchmark against your expected workloads. PAE 'Page Alternate Extensions' is frankly a bit of a haque to allow acce= ss to more than 4GB RAM by giving each process it's own separate 4GB address sp= ace, rather than sharing the space between all processes. Any one process can= not grow beyond 4GB, but the total over all processes can be more than 4GB. = There is support in FreeBSD but with some severe limitations. Many drivers are= not compatible with a PAE system. > and then if I check >=20 > real memory =3D 3757965312 (3583 MB) > avail memory =3D 3678597120 (3508 MB) >=20 > I do not know why this happens. That number is the amount of memory less what is wired down for the kerne= l. If you're on a 'big' system -- with lots of RAM -- then the kernel itself= has to be larger because it needs to allocate memory to contain page mapp= ings etc. etc. Approximately 500MB consumed by the kernel is not unreasonable = for such a machine. Cheers, Matthew --=20 Dr Matthew J Seaman MA, D.Phil. Flat 3 7 Priory Courtyard PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW, UK --------------enig9DC83E041CB514700A69BA14 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFFCRj18Mjk52CukIwRA9HIAJ9M6zEqeq+LVOYrfqrYlxqlORKSIwCeLCer 19apcqFREyruyTCqehcHXXc= =tLCp -----END PGP SIGNATURE----- --------------enig9DC83E041CB514700A69BA14--
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