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@xxxxxxxxx
[PATCH] Fix mem= options
Patch from "Randy.Dunlap" <rddunlap@xxxxxxxx>
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.