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> The default swap policy on DU (Digital Unix, Tru64, ...) is > "no overcommit", which means that you will get a memory allocation > error if swap space equal to the maximum run requirements cannot > be reserved in advance. > > The default swap policy on most linux setups is "overcommit", which > means that it will go ahead and try to run your program anyhow, and > only error out on memory allocation failure is in fact triggered > during the course of your run. [snip] Ethan, Thanks; I'd had no idea that there was such a thing as swap policy, nevermind that it was different on tru64 and linux. However, I suspect that this isn't the problem, because setting "no overcommit" on linux doesn't reproduce the CCPALC error message seen on the alpha (although I have yet to try changing the alpha to lazy/overcommit allocation, because it's running another long job; but I'll do that as soon as that job's over). Thanks again, Pete > "No overcommit" is a safer policy in the sense that you don't want > to get 24 hours into a long run and only then die because of > inadequate swap space. Better to reserve the swap in advance and > be guaranteed that you will not run out. On the other hand, > in this mode you obviously must provide larger swap areas. > > The command to change swap policy for recent linux kernels is > "no overcommit" > echo -n 1 > /proc/sys/vm/overcommit_memory > "overcommit" > echo -n 2 > /proc/sys/vm/overcommit_memory > The default is actually 0, which is some heuristic hybrid with > unpredictable behaviour. > > To change swap policy for DU4/Tru64 is messier: > > This is from the docs. They use "eager" to mean "no overcommit", > and "lazy" to mean "overcommit". > > The default swap mode is the "eager" swap mode. > To switch to "lazy" swap mode, as root rename the file > "/bin/swapdefault" to "/sbin/swapdefault.sav". > Then reboot the system. To switch back, rename the file back > to it's original name and reboot again. > > On either linux or Tru64 you can of course also addess the > problem by adding [a lot] more swap space. > > > -- > Ethan A Merritt > Biomolecular Structure Center > University of Washington, Seattle WA > Pete Meyer Fu Lab BMCB grad student Cornell University
