On Tue, 2009-02-03 at 23:49 -0800, Bill Broadley wrote: > Chanoch (Ken) Bloom wrote: > > On Tue, 2009-02-03 at 10:28 -0800, Bill Broadley wrote: > >> Chanoch (Ken) Bloom wrote: > >>> I'm upgrading an x86 > >> Not x86-64? > > > > There's two machines with this problem. One is really an x86. The other > > is an amd64, but it's running a totally 32-bit system since it shares > > home directories by NFS with the first machine (and a couple other > > 32-bit only machines). > > There is no problem use a 64 bit NFS server and a 32 bit NFS client.
No there isn't, but when people are compiling binaries for one it can can become confusing if they log in on the other and things don't work. > > With regard to the amd64, I'd like to have it run a 64-bit kernel with a > > 32-bit userspace > > Why? Things like mplayer (with a bunch of codecs), flash, java plugin, dvd > playback, video encoding, etc "just work". I've not seen any problems with > google earth 5.0, picasa, firefox (with plugins), etc. > > >, but the machines are running Gentoo, and I don't know > > how to do that in Gentoo. > > Unless recently I always installed 32 bit machines for anything with any sort > of desktop duty. I didn't want a chroot, didn't want to main two > environments, didn't want alot of extra hassle... not to mention 4 or more GB > of ram is pretty pricey. These days 4GB ram cost $50 or so, things are much > more mature. > > > (I'm looking at switching these machines to Debian in the long run, and > > I'll probably start testing that on one machine after lenny is released > > in a couple weeks, so in the long run I may not need to solve the > > kernel/userspace thing in Gentoo.) > > I've heard of folks running hybrid with debian, personally I'm running ubuntu > and it keeps me happy.... I was 100% redhat er, umm, for almost a decade. > > > So you're saying that a 32-bit kernel will map devices in into the 4GB > > address space in such a way that they hide physical RAM, regardless of > > whether you're using CONFIG_HIGHMEM4G or CONFIG_HIGHMEM64G, and that a > > 64-bit kernel will map devices differently. Is this right? > > Er. You are seeing 3GB or so of ram because some devices like video cards > take memory in the bottom 4GB by default, some PCI devices can only address > memory in the bottom 4GB. There are various approaches to handling this, > linux supports bounce buffers so an I/O device can write to the lower 4GB, > then the kernel copies it to wherever user space expects it (which can be > above or below 4GB). PAE is definitely required, as Cam mentioned I'd try the > HIGHMEM4G first. If that doesn't work see if the BIOS mentions anything, then > if that doesn't work try the 64G setting. > > Unless of course you just want to upgrade to a 64 bit kernel. > > > The definition is probably "Machine Register Size". Pointers, ints, and > > Which registers? Int? Floating point? SSE? General registers, which are typically used for addresses and ints. > > addressable memory should go along for the ride because it's convenient > > Addressable memory isn't a particularly good one, after all the last 5 > generations or so of intel chips could address 64GB, but only had 32 bit > pointers (4GB worth). Sorry. I meant the memory addressable by a userspace process. > > to do it that way, but note: > > * an int on amd64 gcc is 32 bits. It's a long that's 64 bits. > > Indeed... although that's a language thing more than anything else. GCC also > supports 128 bit floats (long double), but that doesn't really say anything > about the hardware. > > > * The DOS memory model (*sticks out tongue*) used 16-bit pointers > > on 16-bit processors, but addressed 1MB of RAM by the use of a > > segment register to choose which "paragraph" of memory pointers > > would refer to. > > Right, much like PAE. Instead of a segment register they play tricks with the > page tables. Hopefully 64 bit pointers will prevent any new hacks in there > area. Lets so most system max out at around 8 Dimms. 2^64 bytes/8 = 2^61 > bytes. So until something bigger than 2048 Petabyte dimms become common we > should be safe. Maybe then ZFS will makes sense ;-) As I said above, I was referring to process-addressible memory. PAE is an issue clearly confined to kernel space. The DOS memory model was in what passed for userspace. --Ken -- Ken (Chanoch) Bloom. PhD candidate. Linguistic Cognition Laboratory. Department of Computer Science. Illinois Institute of Technology. http://www.iit.edu/~kbloom1/
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