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On Wed, 19 Dec 2007, Nico Schottelius wrote: >> If you're running tons of memory, it >> really is better to run a 64-bit kernel if possible. > > Sure? Afaik that results in a bit slower access to memory and appart > from being able to address MUCH more memory doesn't change the > situation. No, generally 64-bit x86 does not slow down things - it might speed things up a bit due to more accessible registers in 64-bit mode. And it does change the situation from VM PoV a lot. In (bearded) God's own words - "... run a 64bit kernel and then the kernel isn't trying the software equivalent of managing a filing cabinet through the keyhole." You will find this recent thread on same topic useful - http://lkml.org/lkml/2007/12/17/7 . > Perhaps I missed something. > > And updating to 64 Bit kernel also implies changing the userland, so > a reinstall would be necessary, wouldn't it? May not be necessary - I recently tried installing Fedora 8 32-bit/PAE on a 8Gb Core 2 box and then upgrading just the kernel to 64-bit and it worked fine except for the 32-bit iptables service having problems running on 64-bit kernel. [Also I hear the closed source nVidia binaries will not work on this setup - so if you don't need such things you will be able to go to a 64-bit kernel w/o reinstalling userspace.] >> I believe there are >> some cases where low memory can be pretty easily exhausted on machines with >> lots of high memory. > > Some minutes ago the third machine of that type freezed. > with 7 GiB of *free* memory, before getting oom+panic. > > Is it possible to debug this issue somehow? Like said in the above thread I referred to you might have better luck with RHEL/CentOS or other "Enterprise" kernels if you want to stick to 32-bit. But the pain is not worthwhile - give 64-bit kernel a shot. HTH Parag | ||||||||||||
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