Date: Tue, 13 Feb 2001 13:44:32 +0000 (GMT) From: Doug Rabson <dfr@nlsystems.com> To: Dag-Erling Smorgrav <des@ofug.org> Cc: <arch@freebsd.org> Subject: Re: sparse core dumps Message-ID: <Pine.BSF.4.31.0102131343270.62815-100000@herring.nlsystems.com> In-Reply-To: <xzpsnlizqtx.fsf@flood.ping.uio.no>
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On 13 Feb 2001, Dag-Erling Smorgrav wrote: > I finally found the time to finish hacking savecore(8) to generate > sparse dumps. The good news is it's even noticeably faster than the > old version :) There's a patch up on freefall: > > http://people.freebsd.org/~des/software/savecore-20010213.diff > > Here's a side-by-side comparison (using a version of savecore(8) that > doesn't clear the dump after saving it): > > root@rsa /var/crash2# time savecore $(pwd) > savecore: reboot after panic: from debugger > savecore: system went down at Tue Feb 13 11:33:22 2001 > savecore: /var/crash2/bounds: No such file or directory > savecore: writing core to /var/crash2/vmcore.0 > savecore: writing kernel to /var/crash2/kernel.0 > savecore /var/crash2 0.17s user 32.25s system 19% cpu 2:48.72 total > root@rsa /var/crash2# time /tmp/savecore $(pwd) > savecore: reboot after panic: from debugger > savecore: system went down at Tue Feb 13 11:33:22 2001 > savecore: writing core to /var/crash2/vmcore.1 > savecore: writing kernel to /var/crash2/kernel.1 > /tmp/savecore /var/crash2 18.29s user 5.62s system 19% cpu 1:59.96 total > root@rsa /var/crash2# du -k vmcore.0 vmcore.1 > 524352 vmcore.0 > 35712 vmcore.1 > root@rsa /var/crash2# cmp vmcore.0 vmcore.1 && echo 'Mrreaow!' > Mrreaow! Cool! > > This is with a 4096-byte block size (equal to PAGE_SIZE), which was > noticeably better than my original choice of 512 bytes. I think the > best overall block size is the crashed kernel's page size, as most of > the holes will originate from (series of) zeroed pages; I tried > 8192-byte blocks (my /var/crash and /var/crash2 file systems have 64k > blocks and 8k fragments) but noticed no improvement. Writing to a file > system with smaller (1024-byte) fragments gave a smaller actual disk > usage but a 50% increase in system time. Probably it should just use getpagesize() to decide what block size to use. -- Doug Rabson Mail: dfr@nlsystems.com Phone: +44 20 8348 6160 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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