Date: Fri, 28 May 2010 19:49:26 +0300 From: Andriy Gapon <avg@icyb.net.ua> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: amd64@freebsd.org, freebsd-fs@freebsd.org Subject: Re: FreeBSD 8.1-Prerelease Panic amd64 w/ZFS.. Message-ID: <4BFFF416.1080901@icyb.net.ua> In-Reply-To: <20100528134549.GA75411@icarus.home.lan> References: <060401cafe37$a411b240$ec3516c0$@net> <4BFF894F.4010008@icyb.net.ua> <20100528134549.GA75411@icarus.home.lan>
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on 28/05/2010 16:45 Jeremy Chadwick said the following: > It is? On amd64, vm.kmem_size (not vm.kmem_size_max) is what has to be > increased. I can point folks to the "official" statement from pjd@ and > some others if need be. For a very long time I questioned this because > for an even longer amount of time we were being told to increase > vm.kmem_size_max. > > vm.kmem_size_max, by default, is already huge on amd64 (~320GB or > something like that). Proof: > > vm.kmem_size_max: 329853485875 > > To the OP: you will need to increase vm.kmem_size in /boot/loader.conf > and reboot the system. "What value do I pick?" With 4GB, I would > recommend you use these two variables: > > vm.kmem_size="2048M" > vfs.zfs.arc_max="1536M" > > This will increase the available kmem, and also limit the ARC size > explicitly to nothing larger than 1.5GB. This should stabilise your > system. > Jeremy, you are correct, I was confused about what kmem_size_max and kmem_size meant. kmem_size_max is what could be available, in principle, for kmem_map. But in practice kmem_map size is auto-set to about 1/3 of physical memory available, this is on amd64. BTW, the "6GB" change you mentioned in your other email was more relevant to kmem_size_max, it was overridden since then with 512GB change. kmem size calculations are very well explained here: http://www.mailinglistarchive.com/freebsd-current@freebsd.org/msg10986.html BTW, I don't see why we set kmem size to a fraction of physical memory on amd64 where we have plenty of KVM available. I don't buy the argument that larger kmem size would allow kernel to exhaust all physical memory which would lead to a "bad thing", e.g. a panic - right now kernel can exhaust all kmem which does lead to a panic. Perhaps, default value of VM_KMEM_SIZE_SCALE should be change to one on amd64? -- Andriy Gapon
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