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On Fri, 25 Jun 2010, Simon Waters wrote:
Gordon Henderson wrote:However, I've no experience of more than 4GB of RAM in a 32-bit system, so just wondering if anyones done this - basically what I'm trying to do is avoid a complete re-install on the box (which is 300 miles away) with 64-bit Debian (although compiling a kernel to cope with the added memory is fine)Any experiences? good/bad/indifferent?Not a lot of experience but my guess is it will "just work" unless the individual processes exceed any of the process limits (which can in many cases be "fixed" with sysctl/ulimit if the values aren't insanely large).
I'm thinking it should "just work" too - done a bit of googling, found one page with a benchmark for 32-bit vs 64-bit and memory access speeds (spread of many GB of RAM) and it didn't find any difference...
Debian have stock "BIGMEM" kernels so compiling your own shouldn't be needed unless you've fiddled here already.
The kernel is already custom, so no real issues toggling the 64GB option and re-compiling.
I have this nagging suspicions that "BIGMEM" is there by default now on Debian for some reason that I can't immediately Google up - but that might have been a special case I was looking at or some such.What process needs that much RAM?I assume some huge database? This is going to be the issue, whether the process really does fit into 4GB address space with the various restrictions that apply.
The database is moderate, (just to store results) but they're playing with lots of data held outside SQL, doing doing "stuff" with it. It's all under NDA so I can't go into the details, but to do with calculating radio widgety wavey stuff between 2 geographic points... A bit specialist, and the LAMP bit just lets them view results - they scp data to it and run their programs. They just want to do more of them, if possible on the same hardware. (Speed isn't an issue, and it's multi-core) It curently runs at about 1-1.5GB.
Probably the sort of thing that "cloud computing" might be good for, but who am I to suggest that they pay Amazon, etc. rather then me...
Gordon -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html