Date: Sun, 27 Mar 2011 19:23:41 -0700 (PDT) From: Luke Dean <LukeD@pobox.com> To: freebsd-questions@freebsd.org Subject: kern.geom.journal.stats.low_mem refers to what? Message-ID: <alpine.BSF.2.00.1103271901080.16486@tower.lukas.is-a-geek.org>
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I've recently set up gjournal on top of gmirror on FreeBSD 8.2. I understand that this setup has a lot of redundant writing. It is working, but I'm not sure I've set it up as efficiently as I should. During prolonged writes, such as copying large files to the file system across the network or producing very large logfiles, the "low_mem" and "skipped_bytes" statisics rise rapidly and the system becomes less responsive. "top" always reports free memory, so I don't think that's the issue. "journal_full" and "wait_for_copy" have never occurred. Here's a sample of what happens after a couple hours of intense writing... kern.geom.journal.stats.low_mem: 5379 kern.geom.journal.stats.journal_full: 0 kern.geom.journal.stats.wait_for_copy: 0 kern.geom.journal.stats.switches: 7543 kern.geom.journal.stats.combined_ios: 265318 kern.geom.journal.stats.skipped_bytes: 935712768 "low_mem" sounds like a bad thing. What could I do to remedy that? Did I make the journal too small? The stats say that "journal_full" has never happened, so maybe not? Is there a setting I should tweak? The Handbook says 1GB is good enough most of the time, but it also says that 3x the amount of physical memory is a good size as well. I compromised between the two and made an 8GB journal for this system that has ~4GB of memory.
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