Re: mem= handling mess.

["H. Peter Anvin" <hpa@zytor.com>]

Dave Jones wrote:
> At some point in time during 2.4, parse_cmdline_early() changed
> so that it handled such boot command lines as..
> 
> mem=exactmap mem=640k@0 mem=511m@1m
> 
> And all was good.  This change propagated forward into 2.5,
> where it sat for a while, until hpa freaked out and
> Randy Dunlap sent in cset 1.889.364.25
> 
> ChangeSet 1.889.364.25 2003/03/16 23:22:16 akpm@digeo.com
>   [PATCH] Fix mem= options
>   
>   Patch from "Randy.Dunlap" <rddunlap@osdl.org>
>   
>   Reverts the recent alteration of the format of the `mem=' option.  This is
>   because `mem=' is interpreted by bootloaders and may not be freely changed.
>   
>   Instead, the new functionality to set specific memory region usages is
>   provided via the new "memmap=" option.
>   
>   The documentation for memmap= is added, and the documentation for mem= is
>   updated.
> 
> This is all well and good, but 2.4 never got the same treatment.
> Result ? Now users are upgrading their 2.4 systems to 2.6,
> and finding that they don't boot any more.
> (See https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=124312
>  for example).
> 
> The "`mem=' is interpreted by bootloaders and may not be freely changed."
> obviously hasn't broken the however many users of this we have in 2.4
> so I don't buy that it'll break in 2.6 either.  As its now in 2.4
> (and has been there for some time), this is something that bootloaders
> will just have to live with.
> 

It was changed to memmap= I thought.  The command line suggested above, for 
example, WILL NOT boot with any correctly operating boot loader. 
Unfortunately, given its history I suspect GRUB is nowhere in that category.

I think telling people to use memmap= instead of mem= is the only sane way to 
deal with this.

What is even more puzzling is that the command line used by the user in that 
question is bogus, and should be *exactly* identical to "mem=512M", but the 
bug report indicates that doesn't work on that machine.  Thus, there is 
something more seriously wrong.

	-hpa