From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH, RFC] panic-note: Annotation from user space for panics Date: Wed, 18 Nov 2009 10:16:28 -0800 Message-ID: References: <1258463404.27437.103.camel@localhost> <20091117235627.GA13469@dvomlehn-lnx2.corp.sa.net> <1258505777.3081.4.camel@calx> <4B043467.8000708@am.sony.com> Mime-Version: 1.0 Return-path: In-Reply-To: <4B043467.8000708@am.sony.com> (Tim Bird's message of "Wed\, 18 Nov 2009 09\:52\:39 -0800") Sender: linux-embedded-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Tim Bird Cc: Matt Mackall , David VomLehn , "dedekind1@gmail.com" , Marco Stornelli , Simon Kagstrom , "linux-embedded@vger.kernel.org" , "akpm@linux-foundation.org" , "dwm2@infradead.org" , "linux-kernel@vger.kernel.org" , "paul.gortmaker@windriver.com" Tim Bird writes: > Eric W. Biederman wrote: >> Matt Mackall writes: >> >>> As much as I like kexec, it loses on memory footprint by about 100x. >>> It's not appropriate for all use cases, especially things like >>> consumer-grade wireless access points and phones. >> >> In general I agree. The cost of a second kernel and initrd can be >> prohibitive in the smallest systems, and if you do a crash capture >> with using a standalone app that is reinventing the wheel. >> >> That said. I can happily run kdump with only 16M-20M reserved. >> So on many systems the cost is affordable. > > Understood. On some of my systems, the memory budget for the > entire system is 10M. On most systems I work with, it is a > struggle to reserve even 64K for this feature. crash_kexec is really a glorified jump. It is possible to do a lot in 64K with a standalone application. If reliable capture of kernel crashes is desirable to an embedded NAND device I expect a semi-general purpose dedicated application for capturing at least dmesg from the crashed kernel and write it to a file on a NAND filesystem could be worth someones time. On general purpose hardware we use a kernel and an initrd simply to reduce the development work of supporting everything and the kitchen sink. My impression is that embedded systems can afford a little more setup time, and a custom compilation, and that the hardware you would like to store things too is much more common. Eric