Date: Fri, 10 Apr 2015 11:16:39 +0200 From: =?windows-1252?Q?Pierre-Yves_P=E9neau?= <Pierre-Yves.Peneau@lip6.fr> To: freebsd-questions@freebsd.org Subject: Re: How FreeBSD manage more than 4GB on 32 bits architecture Message-ID: <552794F7.60306@asim.lip6.fr> In-Reply-To: <20150409190722.1260.qmail@ary.lan> References: <20150409190722.1260.qmail@ary.lan>
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[-- Attachment #1 --] -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 On 04/09/2015 09:07 PM, John Levine wrote: >> So, I've the required hardware I think. My problem is to find out >> how FreeBSD can use this mechanisms. But I'm realizing that it >> may be not a kernel issue, because it's an hardware functionality >> which should works with Linux too. Right ? > > Right. I don't think I've ever seen a machine with a 32 bit > architecture that could address more than 36 bits of real memory. > If you need more than that, you use a 64 bit architecture. But it exists :-) We have a simulate environment, and a real prototype which have 24 clusters (i.e. 96 CPUs) and 96GB of physical memory. All of this with 32 RISC processors. > As far as I know, 32 and 64 bit versions of FreeBSD use the same > virtual memory manager, and there's no inherent reason you > couldn't manage large physical memories with 32 bit code. But I > can tell you that you will be sorry if you try. If the physical > memory is much bigger than a program's logical address space, you > have to do some sort of tricks for programs to access all of the > memory. If the memory is only a few times larger than the address > space, say 36 bits, it's OK to limit programs to 32 bits and hope > you have enough of them to keep the memory busy. Or you use tricks > like large shared files that are mapped in and out of the program's > address space, typically with a blizzard of TLB misses every time. > > But if you have 40 bits, you really want something that can address > 40 bits which in today's world means a 64 bit architecture. Take a > look at ARMv8 which handles 48 bit physical addresses and is > supposed to have low power implementations for smartphones and > other power-constrained environments. > > R's, John > > > _______________________________________________ > freebsd-questions@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-questions To > unsubscribe, send any mail to > "freebsd-questions-unsubscribe@freebsd.org" > Thank you for your advices. I agree with you, but it's an internship, I can't say "Please, would you like to change all your CPUs for me ?" :-) Moreover, the main challenge is to deal with huge memory with 32 bits processors (only RISC), I think it's really interesting. - -- +---------------------------------------------------------------+ | Pierre-Yves Pneau (#3361856) | SoC - LIP6 - UPMC | | Couloir 24-25 Bureau 417 | first.last@lip6.fr | | 4 place Jussieu 75252 Paris Cedex 05 | +33 1 44 27 54 15 | +---------------------------------------------------------------+ -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJVJ5T2AAoJEPy7VC2L9m/AO1oP/3fNrX7QZgZgT1QdT5P/niNH vtLCXED7tay0qylBVqXqLM4CVIPZGYnsU81G3prpD+tZK3zLWGvQ13HdEVZXHrm2 oYZUtpaUQ7AN7dgkD2Hq5eo2rgzuilnm9GkjMPFMKhEq0m4vhlzaVj2FH0oxshCT 3t8o2upIW/acEaQtwuUtS0tL5e7guEv75+r+mD5Ip3l13CPZUizvwv4LzCU5LbxF 07DA68iIjJleCRihoLJGMjXMc6O3FiQjsZIqtyWXV3SkCrTDRMh0Ae+08D2SHLeT eVJhzdFZ7DFP6C/6xv1QEmTEyJwNwmJFc1PO+UhgISusvErmRDyevDRwfEsuUaC1 +XSSulKm27q6d2Rbp1nmr+mSZZ6L3faKYjgN9rpUJy1N03cW0wKceIzeIIy99kXA 3B1LAx0c8sm+RJP9KiSMCus1qKvdfTRn8eglEcR030+lHZp6eHGEPFm0DMaROdjy D17l8V4czul0Zn+NbwzYRP3TP4rTMDsFKj+s16oQQw+4+vWLrAif1mOJbgxa25vg pXpXH7zF4j7cLWc+d8Lz91Ql0mqYnG1ZC0BkasiNRPyQue0jxXDR7wDhHT9azfSw W2ZEWGicTY9oJE4N7NEvq4eWD+2iLM8Xvv1OgGW0Kc+xrS08YjzOxkbiH0boQLXp NnA9RAJsDoahZj+1YoMs =hhyy -----END PGP SIGNATURE----- [-- Attachment #2 --] U' T-ob , خʺn, |")/'B f:<M:%& ȍf1O,NZ+.aGx ,ܢVsɂ.m'JIP8ղ' Ιp4sRNEfZl "YuTYpJk eW{ kjSc>~͌ s 2zդjZje+zxG^^gWxYN6[[ .29b '5!gzTCt}4<hr$eZ2 Q@ 5C!ͳ~q mGOh&`3,?=Ãm nU}d?} ~됎C8}P=Hn[yIH1*ݤ a/C#ڠ ,|co-S"|ꋒ]:#&=xS9M^;"{<"DRs*8~_{
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