[syslinux] Syslinux Mem= greater than 4096M

[Kevin Sullivan]

Thanks to everyone that offered advice and opinions on this issue.  It
looks like the linux.c32 is one option, but I just now tried memmap= and it
worked on the first attempt.

The problems (challenges) with the e820 map is that it is so highly
variable from system to system and we are attempting to make a boot USB
distribution that works on everything from netbooks to enterprise servers.
Currently, this means booting on multiple vendors' machines that could have
anywhere from 1 GB to 1.5 TB of system RAM.  And some of the e820 memory
maps are extremely convoluted.

Thanks for your assistance and thanks for your participation in creating
something as important to the world of computing as syslinux is fantastic.

-Kevin

On Sat, Feb 4, 2012 at 6:32 AM, Gene Cumm <gene.cumm at gmail.com> wrote:

> On Sat, Feb 4, 2012 at 01:00, Kevin Sullivan <ksullaustin at gmail.com>
> wrote:
> > On Fri, Feb 3, 2012 at 10:33 PM, Gene Cumm <gene.cumm at gmail.com> wrote:
> >
> >> On Fri, Feb 3, 2012 at 22:48, Kevin Sullivan <ksullaustin at gmail.com>
> >> wrote:
> >> > Hi Shao,
> >> >
> >> > I have several boot options, but here is one example:
> >> >
> >> > LABEL less
> >> >    MENU LABEL Up to 64 GB System RAM
> >> >    KERNEL /boot/vmlinuz-3.1.10-b1
> >> >    APPEND pci=nommconf vga=773 mem=256M
> initrd=/boot/initrd-3.1.10-b1.img
> >> >
> >> > This boots a Linux kernel that can only "see" 256 MB.  If I set
> mem=4097
> >> or
> >> > greater, I get the error message.
> >>
> >> Same error with 'mem=4352M' ?  mem should be interpreted by the core
> >> for load alignments by the Syslinux core.
> >>
> >> --
> >> -Gene
> >>
> >> Gene,
> >
> > Interesting.  It does not show the error with mem=4352M.  However, the
> > kernel is only showing about 3.3 GB total RAM after it boots.  I do not
> > understand the concept that you mention of "mem should be interpreted by
> > the core for load alignments by the Syslinux core.  Could you give
> insight
> > into how you picked this number and/or how I can select safer larger
> > numbers?  For my particular situation,  I probably only need to reach the
> > mem=8192M range.  As an FYI, mem=4095M only gives me 3.0 GB free, so your
> > answer is already proving helpful.
> >
> > Thanks,
> >
> > -Mark
>
> Typically the Syslinux code common to all variants will load
> kernels/initrds at the top of memory (with padding for alignment).
>
> Sounds like you have a "hole" from 3GiB to 4GiB.  You can use
> com32/modules/meminfo.c32 to confirm.  It's in the e820 map.  If you
> have difficulty interpreting it, I'd suggest taking a screen shot
> (cell phone cameras can sometimes work if the picture isn't blurry)
> and post a link to it.  It would be better if the picture were clear
> and shrunk to about 1024x768 (or at least a warning on the file size).
>
> You could also try to copy com32/modules/linux.c32 to /boot/ and try:
>
> LABEL less
>    MENU LABEL Up to 64 GB System RAM
>     COM32 /boot/linux.c32
>    APPEND /boot/vmlinuz-3.1.10-b1 pci=nommconf vga=773 mem=4352M
> initrd=/boot/initrd-3.1.10-b1.img
>
> I'd guess this will give similar results but if you used mem=4097M it
> will likely succeed.
>
> --
> -Gene
>
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