Messages in this thread | | | Date | Thu, 25 Sep 2008 10:55:19 +0200 | From | Ingo Molnar <> | Subject | Re: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected |
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* Rusty Russell <rusty@rustcorp.com.au> wrote:
> I can't see a neater way down this path, and I don't want to lose > const. > > I can see three alternatives: > 1) An ONSTACK_CPUMASK(name) macro which declares "struct cpumask name[1]" or > "struct cpumask *name". Same idea as yours, without the typedef. > 2) Use a normal struct for cpumask, make everyone use pointers, but have an > struct cpumask *alloc_stack_cpumask() which uses alloca() for small > NR_CPUS. > 3) Same, but just use kmalloc everywhere. Optimize important cases by hand. > > Anyone see a better way?
since most of the important cpumasks in high-perf codepaths are already pre-constructed and embedded in some existing object (say task_struct), i think a variant of #3 is the best approach:
- get rid of cpumask_t and use 'struct cpumask' everywhere.
- do not expose normal kernel code to struct cpumask's definition, only declare the type via 'struct cpumask;' in sched.h - a'la kmem_cache_t.
- even hide the structure from sched.h - use an extra indirection for struct cpumask *cpus_allowed in task_struct and be done with it.
- have normal cpumask object alloc/free codepaths.
- optimize any remaining important cases by hand, if needed. (the scheduler mostly)
(wrt. #2, alloca() is a nightmare i think.)
Ingo
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