Date: Sat, 23 Apr 2005 10:09:41 +0200 From: "Daniel Eriksson" <daniel_k_eriksson@telia.com> To: "'FreeBSD Current'" <freebsd-current@freebsd.org> Subject: RE: Serious I/O problems (bad performance and live-lock) Message-ID: <!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAA0VcX9IoJqUaXPS8MjT1PdsKAAAAQAAAA5xh4prxQBkmZLv9A9nCvPwEAAAAA@telia.com> In-Reply-To: <!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAA0VcX9IoJqUaXPS8MjT1PdsKAAAAQAAAAKDq8qQ2O9UK7PKMOCt2NqwEAAAAA@telia.com>
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Here are some further observations and speculations. On a newly booted system, this is what happens: 1. Start a "dd if=/dev/zero of=/usr/test bs=128k". 2. While looking at 'top', "Inact" grows and "Free" shrinks. 3. Once "Free" has bottomed out, "Inact" stops growing (naturally). 4. 'dd' continues to put a load on the VM system, eventually forcing most processes to be swapped out (illustrated by the "RES" column showing a very low number for all but a few processes). This takes 30-60 seconds after "Free" has bottomed out on my machine. 5. At this point the machine is mostly useless because it can take several minutes to run a simple 'ls'. 6. After a little while in this useless state the machine becomes so unresponsive that it no longer accepts any input, not even a CTRL-C to end the 'dd' process. Breaking into DDB and killing 'dd' from there works though. I tested this again this morning on a system compiled from sources dated 2005.04.23.05.10.00 (just after the commit to kern_exit.c by David Xu), but the behavior seems to be mostly the same. I did not manage to get it to completely lock up though, but I only tested it once on my UP server. /Daniel Eriksson
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