On 2016-04-06 19:42, Nix, Robert P. wrote:
Let z/VM worry about the memory and I/O. It¹s good at it, and Linux
will
not out-guess its decisions. And, rather than caving to the developer¹s
demands, ask them to let you show them what you can do. Size the
virtual
machine so that it just barely pushes into the swap. If swap is 0, then
the machine has (possibly way) too much memory. If it is using 50% of
the
swap, then the machine needs more virtual memory. It NEVER needs more
swap; letting Linux swap under z/VM is just plain stupid.
Note that there is one case where this doesn't work: If the application
allocates a lot of virtual memory but its working set is small and would
fit into RAM. There the size of the swap directly impacts if the memory
requests will be satisfied by the kernel or not. This behavior can be
tuned based on the information in [1].
Kind regards
Philipp Kern
[1] https://www.kernel.org/doc/Documentation/vm/overcommit-accounting
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