David wrote:
> I prefer Choice B because it does not force mempolicies to have any
> dependence on cpusets with regard to what nodemask is passed.
Yes, well said.
> It would be very good to store the passed nodemask to set_mempolicy in
> struct mempolicy,
Yes - that's what I'm intending to do.
> If the cpuset has fewer than four nodes, the behavior
> should be undefined (probably implemented to just cycle the set of
> mems_allowed until you reach the fourth entry).
I do intend to implement it as you suggest. See the lib/bitmap.c
routines bitmap_remap() and bitmap_bitremap(), and the nodemask
wrappers for these, nodes_remap() and node_remap(). They will
define the cycling, or I sometimes call it folding.
I would have tended to make this folding a defined part of the API,
though I will grant that the possibility of being lazy and forgetting
to document it seems attractive (less to document ;).
> That [running in a cpuset with fewer nodes than used in a memory policy
> mask] is the result of constraining a task to a cpuset that obviously
> wants access to more nodes -- it's a userspace mistake and abusing
> cpusets so that the task does not get what it expects.
Nah - I wouldn't put it that way. It's no mistake or abuse. It's just
one more example of a kernel making too few resources look sufficient
by sharing, multiplexing and virtualizing them. That's what kernels do.
--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <[email protected]> 1.925.600.0401
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- References:
- [patch 1/2] cpusets: extract mmarray loading from update_nodemask
- From: David Rientjes <[email protected]>
- [patch 2/2] cpusets: add interleave_over_allowed option
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- Re: [patch 2/2] cpusets: add interleave_over_allowed option
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