On Mon, May 26, 2008 at 06:07:24PM -0400, Kent A. Reed wrote: > Jeff: > > I thought I'd take this offline rather than add to the emc_users burden.
Actually, this is a fine topic for the emc-developers list, if you're a member there. I'm sending a copy to that list. > A few weeks ago, you said in the footnote in your reply to my emc_users > message: > > >PS It's for this reason that the linuxcnc.org / ubuntu 6.06 kernel was > >built with the 1GB memory limit configuration option chosen -- > >unfortunately the name of the option escapes me at the moment. so most > >users who have "run into" this problem have run into the form "linux > >doesn't recognize all my memory" > > > I checked the kernel configuration file on my installation from the > ubuntu 6.06-based LiveCD and found CONFIG_NOHIGHMEM=Y. Running the 6.06 > LiveCD live on a box equipped with 1GB of RAM and looking at the dmesg > output I see I have 896MB LOWMEM available. I added some words to the > Wiki Hardware Requirements page about the memory limit accordingly. > > So far so good, but I "assumed" this to be true also for the new ubuntu > 8.04-based LiveCD and said as much on the wiki. I think I got carried > away with myself. > > I just downloaded the 8.04 LiveCD and ran it live on the same 1GB > desktop machine. According to the kernel configuration file, NOHIGHMEM > is not set but CONFIG_HIGHMEM4G=Y. Looking at the dmesg output shows > 95MB HIGHMEM available and 896MB LOWMEM available. I assume it would be > equally happy loading 2GB or more. > > It looks to me that the large memory problem with RTAI can trip up > unsuspecting users after all, just not with the earlier LiveCD. Have I > overlooked something here? (Like I don't know enough about the mechanics > of booting from a LiveCD to know if there's a GRUB-like "mem=<limit>" > buried somewhere.) > > This isn't earthshaking stuff, but I prefer making rough spots known to > users in advance. Some will drive straight into the potholes anyway but > at least they can't complain they weren't warned. The basic story is this: we independently discovered the 1GB memory limit way back when we were building kernels for ubuntu 5.10, and put in the workaround 1GB memory limit in the kernel configuration. Fast forward to 8.04, where we had read on the mailing lists that RTAI 3.6 had finally fixed this 1GB bug. In fact, some early testing looked promising, so it made it into the CD image you now have. Unfortunately, the bug with >1GB RAM systems just seems to take a bit longer to manifest than we expected, and eventually it will bite. I am pretty sure that Alex is going to build a fresh kernel package when rtai 3.6.1 is released, so anybody getting updates from the net will have the 1GB problem fixed. Until then, special boot parameters are needed. > PS - I'm unclear about who actually built the 8.04 LiveCD---you, Alex, > whoever---so I'm responding just to you. As far as 8.04 goes, Alex has built the packages for 32-bit systems, as well as the live CD. I helped a bit with the packaging and source code, and I built the packages for 64-bit systems. Jeff ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
