On Mon, 24 Sep 2007 18:18:30 +0530 Balbir Singh
<[email protected]> wrote:
> Peter Zijlstra wrote:
> >>> Only kswapd can do this, direct reclaim has deadlock potential.
> >> Yes, but not in all cases, do you want to add any gfp_mask
> >> based smartness for direct reclaim?
> >
> > gfp_mask doesn't carry the needed information. It depends on whether
> > the current context holds a rcu_read_lock().
> >
>
> What I meant was that nobody would hold rcu_read_lock() and pass
> gfp_mask of GFP_KERNEL in scan_control or to do_try_to_free_pages()
>
> > so something like:
> >
> > rcu_read_lock()
> > foo = kmalloc(sizeof(foo))
>
> At this point, you really can't use GFP_KERNEL, since rcu_read_lock()
> disables pre-emption in the current kernel, ideally you should see
> a might_sleep() BUG.
>
> > new_slab()
> > __alloc_pages()
> > try_to_free_pages()
> > synchronise_rcu() <-- deadlock
> > rcu_read_unlock()
I guess I've been using preemptibe rcu for way too long. Would need to
clean up some of -rt to make this true there, but should be doable
indeed.
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