Re: [PATCH 3 of 3] KEXEC: Allocate crash structures in low memory

[Tim Deegan <tim@xen.org>]

At 15:51 +0000 on 29 Dec (1325173875), Jan Beulich wrote:
> >This is part of the "min" option which is trying to have the least
> >possible impact.  The idea is to have this in low memory, use the
> >"console_to_ring" boot option to copy dom0 dmesg into conring, and pass
> >its physical address and size in a crash note, so that the crash kernel
> >environment grab it all.
> 
> Why is the console ring *that* important? I would have thought
> that proper register values and stack contents are much more
> significant for analysis of a crash.

The console ring has been _very_ useful in diagnosing bugs from field
reports, especially things like guest-level watchdog timeouts and
refcounting errors that cause a crash after the interesting event has
passed.  If nothing else it lets you verify the user's description of
the system, and saves a round-trip of 'please try to set up a serial
logger and reproduce the bug').

(I agree, though, that using a 64-bit crash kernel would be a much
better idea).

Tim.