Date: Thu, 27 Jan 2011 14:53:10 -0500 From: John Baldwin <jhb@freebsd.org> To: Warner Losh <imp@bsdimp.com> Cc: src-committers@freebsd.org, Pawel Jakub Dawidek <pjd@freebsd.org>, Ken Smith <kensmith@buffalo.edu>, Alexander Motin <mav@freebsd.org>, "Robert N. M. Watson" <rwatson@freebsd.org>, svn-src-projects@freebsd.org Subject: Re: svn commit: r217828 - projects/graid/head/sys/geom/raid Message-ID: <201101271453.10305.jhb@freebsd.org> In-Reply-To: <4D41C29A.5020100@bsdimp.com> References: <201101251534.p0PFY7cF039182@svn.freebsd.org> <7FD27004-581F-4FED-858D-5819562CF111@freebsd.org> <4D41C29A.5020100@bsdimp.com>
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On Thursday, January 27, 2011 2:08:10 pm Warner Losh wrote: > On 01/26/2011 08:45, Robert N. M. Watson wrote: > > On 26 Jan 2011, at 15:42, John Baldwin wrote: > > > >> On Wednesday, January 26, 2011 10:06:47 am Ken Smith wrote: > >>> On Wed, 2011-01-26 at 11:45 +0200, Alexander Motin wrote: > >>>> Those who want maximum robustness should use dedicated > >>>> drive on the most trivial dedicated controller to make dumping reliable. > >>>> If we are going above that - there are always some compromises. > >>> Please remember this statement when I change dumpdev from "AUTO" > >>> to "NO" in /etc/defaults/rc.conf shortly after branching stable/9. :-) > >> No, I still think this is the wrong answer. Kernel dumps are not inherently > >> unreliable to the point that we should not enable them by default. However, > >> turning dumps off is a good way to prevent developers from debugging non- > >> trivial bugs that are only triggered under real-world workloads. > >> > >> I think we should strive to make our dumps as reliable as possible, but > >> nothing in our system is perfect (hence bugs), and if we are going to require > >> absolute perfection for kernel dumps before enabling them by default then we > >> might as well not ship anything at all as I can _ensure_ you the rest of the > >> system we ship is _not_ absolutely perfect. > > I think the real constraint on shipping with dumps enabled remains a disk space consideration. If you have a problem triggering a kernel bug, you're going to generate quite a few crash dumps in short order, and for many users, that result is not good. But the answer there may be better savecore behaviour: perhaps we should keep the last (n) (where n is small -- perhaps 2) dumps by default, with a way to mark dumps that should be saved longer. minidumps have made the world better in some ways, I can't help wonder whether that could be refined further... > > I don't suppose there's a way that savecore could be hacked to convert a > 'full' dump into a 'mini' dump? Well, minidumps are already enabled by default so I think that is less important. Probably savecore's policy needs to change so that it saves the most recent N dumps rather than the oldest N dumps and that something like minfree needs to be enabled by default. -- John Baldwin
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