Date: Mon, 13 Oct 2014 00:56:09 -0400 (EDT) From: Terry Kennedy <TERRY@tmk.com> To: freebsd-arch@freebsd.org Subject: [rfc] Add boot-time warning messages to PAE kernels Message-ID: <01PDOI9M51BK0003PW@tmk.com>
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[Inspired by an unrelated email conversation with jhb@]
On the FreeBSD forums and also elsewhere, people frequently ask questions
about enabling PAE. Generally, this is because they don't know that amd64
kernels will run on their hardware.
I initially proposed a static warning message, similar to the ones that
happen when a kernel is built with INVARIANTS or WITNESS, with some sort
of warning that "You probably don't want to do this". On thinking it over
and discussing with jhb@, I think there are three scenarios that could be
addressed:
1) Boot PAE kernel on any amd64-capable processor - display a warning
message stating that the user should consider using the amd64 kernel
instead.
2) Boot PAE kernel on any processor - display a warning message that
driver support is limited on PAE kernels and that they receive less
testing than non-PAE kernels.
3) [Possibly] Boot i386 kernel on amd64-capable system w/ > 4GB of RAM -
display an informational message that the user should consider using
the amd64 kernel instead.
This way, anyone that still needs to run a PAE kernel can, but the users
who choose it by accident or mistake will be guided to the amd64 kernel.
Adding a similar message to i386 kernels on amd64-capable hardware w/ more
than 4GB of RAM will likewise direct those users toward a more optimal
kernel. I mention this because I was having a conversation with a user who
was trying to get ZFS going but "ran out of memory" on a 12GB system due
to using the i386 kernel.
All of this information (processor capability flags and memory size)
is available early enough in the boot process that the messages can be
displayed near the beginning of the kernel messages.
Non-amd64-capable systems that have > 4GB were always a small subset of
the population, and that hardware has aged enough that much of it is no
longer used in its original role as business servers. These are pre-Socket
604 systems, for example. amd64-capable hardware has been available for
more than 10 years from both AMD and Intel at this point.
Terry Kennedy http://www.tmk.com
terry@tmk.com New York, NY USA
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