Messages in this thread | | | Date | Tue, 27 Sep 2016 13:41:30 -0600 | From | Chris Friesen <> | Subject | help? usage of indirect per-cpu variables |
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Hi,
I'm trying to wrap my head around indirect percpu variables, and I'm hoping someone can school me on how they work.
For example, in mm/slub.c we have "struct kmem_cache *s". s->cpu_slab is a per-cpu variable, so we access it with something like:
c = raw_cpu_ptr(s->cpu_slab);
and then a bit later on we do
object = c->freelist;
So far so good. Essentially the raw_cpu_ptr() macro applies a unique per-CPU offset to s->cpu_slab to generate "c" which is a real pointer so we can dereference it to get c->freelist.
What confuses me is how we can do something like this:
this_cpu_cmpxchg_double(s->cpu_slab->freelist, s->cpu_slab->tid, object, tid, next_object, next_tid(tid))
If s->cpu_slab is a special pointer that needs to be accessed only via the per-CPU macros, then how is it valid to specify "s->cpu_slab->freelist"? Since s->cpuslab isn't actually a valid address, how can we dereference it?
Thanks, Chris
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