Date: Fri, 04 Mar 2011 08:23:29 -0500 From: Adam McDougall <mcdouga9@egr.msu.edu> To: freebsd-fs@freebsd.org Subject: Re: kmem_map too small with ZFS and 8.2-RELEASE Message-ID: <4D70E7D1.5030205@egr.msu.edu> In-Reply-To: <1299232133.18671.3.camel@pc286.embl.fr> References: <1299232133.18671.3.camel@pc286.embl.fr>
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On 03/04/11 04:48, Mickaël Canévet wrote: >> I'd use vm.kmem_size="32G" (i.e. twice your RAM) and that's it. > > Should I also increase vfs.zfs.arc_max ? > > Do you have any idea why the kernel panicked at only 8GB allocated ? > > Thank you I believe ARC allocations in kmem can become fragmented, so when it is searching for a place to store a new contiguous segment of memory, the remaining fragmented free spaces may all be too small. I also set vm.kmem_size to about twice the amount of ram to help it avoid this issue. I suspect if kmem is badly fragmented then performance of ZFS can downgrade, so that is another reason to keep kmem bigger.
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