Date: Wed, 03 Feb 2010 04:18:21 +0100 From: Rolf Nielsen <listreader@lazlarlyricon.com> To: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: kmem_size / arc_max ratio Message-ID: <4B68EAFD.5070400@lazlarlyricon.com>
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Hello everyone, I recently installed more RAM in my computer; increased it from 4GB to 8GB. Mainly to be able to use a larger arc for zfs. Now my question is, how much memory does the kernel need apart from the arc? I currently have kmem_size_max 512MB bigger than arc_max. I haven't run into any problems so far. I use my computer as desktop only, running WindowMaker and normally having xconsole, emiclock, firefox with 5+ tabs, thunderbird, amsn, sunbird, thunar, ktorrent and upto 5 or 6 xterms. My loader.conf looks like this: vfs.root.mountfrom="zfs:sysroot" vm.kmem_size_max=5G vm.kmem_size=5G vfs.zfs.arc_max=4608M vm.pmap.pg_ps_enabled=1 zfs_load="YES" nvidia_load="YES" I am considering increasing kmem_size, kmem_size_max and arc_max by 1024MB each. The idea behind that, is that when I had 4GB RAM I had kmem_size and kmen_size_max set to 2GB and never had any trouble with user memory running out, so I believe 2GB user memory should still be enough. Please correct me if I'm wrong. ;) Anyway, the main question is, should 512MB difference between kmem and arc be enough, or should I increase it? Or could I even decrease it? I've had very noticably increased performance with larger arc size, so I would like to set it as high as possible without causing problems for or degradation of other kernel tasks and/or user applications. Please let me know if you need any further information about my system. Cheers, Rolf Nielsen
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