Messages in this thread | | | Date | Mon, 18 Feb 2008 16:46:28 -0800 (PST) | From | David Rientjes <> | Subject | Re: [RFC] bitmap onto and fold operators for mempolicy extensions |
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On Sat, 16 Feb 2008, Paul Jackson wrote:
> Let's say an application has specified some mempolicies > that presume 16 memory nodes, including say a mempolicy that > specified MPOL_F_RELATIVE_NODES (cpuset relative) nodes 12-15. > Then lets say that application is crammed into a cpuset that only > has 8 memory nodes, 0-7. If one just uses bitmap_onto(), this > mempolicy, mapped to that cpuset, would ignore the requested > relative nodes above 7, leaving it empty of nodes. That's not > good; better to fold the higher nodes down, so that some nodes > are included in the resulting mapped mempolicy. In this case, > the mempolicy nodes 12-15 are taken modulo 8 (the weight of the > mems_allowed of the confining cpuset), resulting in a mempolicy > specifying nodes 4-7. >
So what is the MPOL_F_RELATIVE_NODES behavior? Is it a combination of nodes_onto() and nodes_fold()?
In your example, the only way we know to use nodes_fold() is if the resultant of nodes_onto() has a weight of 0. An MPOL_F_RELATIVE_NODES nodemask for 4-6, for example, works fine in your case of a cpuset with memory nodes 0-7 and no fold is required.
So it's easy enough to do this:
case MPOL_INTERLEAVE: if (flags & MPOL_F_RELATIVE_NODES) { nodes_onto(pol->v.nodes, pol->user_nodemask, cpuset_context_nmask); if (nodes_empty(pol->v.nodes)) nodes_fold(pol->v.nodes, pol->user_nodemask, nodes_weight(cpuset_context_nmask)); } else { ... } break;
But what if we require a combination? Say the user asked for a policy of MPOL_INTERLEAVE | MPOL_F_RELATIVE_NODES over nodes 4-8 in a cpuset constrained to mems 0-7? Should the resultant be 0,4-7 (combination of nodes_onto() and nodes_fold()) or simply be 4-7 (just nodes_onto())?
And what if the MPOL_INTERLEAVE | MPOL_F_RELATIVE_NODES nodemask is 0,4-8 in the same cpuset constrained to mems 0-7? Should the resultant be
- 0,4-7 (nodes_onto() and nodes_fold()),
- 0,4-7 (just nodes_onto()), or
- 0-1,4-7 (nodes_onto(), nodes_fold(), and shift)?
The last option, 0-1,4-7, is the only one that preserves the same weight as the relative nodemask.
David
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