[syslinux] Syslinux Mem= greater than 4096M

[Gene Cumm]

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