Messages in this thread | | | Date | Wed, 23 Jul 2008 10:45:18 -0700 | From | Mike Travis <> | Subject | Re: [PATCH 1/8] cpumask: Replace cpumask_of_cpu with cpumask_of_cpu_ptr |
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Rusty Russell wrote: ... >> Another thought I had is perhaps cpumask.h should define something that >> indicates a "huge NR_CPUS count" that is used globally to trigger things >> like kmalloc of cpumask variables, instead of declaring them on the >> stack...? Or (as has been discussed in the past), maybe a new cpumask_t >> type will be needed? > > AFAICT the final answer has to be a get_cpu_mask()/put_cpu_mask(), which > sleeps and doesn't nest (so we can use a pool allocator). Of course, that > kind of analysis is non-trivial, so I suggest that's not for this merge > window... > > Want me to try something and see if it boots? > Rusty.
Hi Rusty,
There are a number of occasions where a function declares a temporary cpumask_t variable on the stack to hold (say) current->cpus_allowed. I tried a couple of options early on to a.) reserve one or two cpumask_t variables in the task struct; and b.) reserve one or two cpumask_t variables per cpu. Both had weird consequences in some usages and since 4096 is *only* 512 bytes, it didn't seem worth the effort. Our next iteration will have NR_CPUS=16384 and therefore removing all stack declared cpumask_t variables is highly desirable.
Your idea of a pool allocator is very interesting... ;-)
Thanks, Mike
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