On Wed, 17 Oct 2012, KOSAKI Motohiro wrote:

quoted

I think this refcounting is better than using task_lock().

I don't think so. get_vma_policy() is used from fast path. In other
words, number of
atomic ops is sensible for allocation performance.

There are enhancements that we can make with refcounting: for instance, we 
may want to avoid doing it in the super-fast path when the policy is 
default_policy and then just do

	if (mpol != &default_policy)
		mpol_put(mpol);

Instead, I'd like
to use spinlock
for shared mempolicy instead of mutex.

Um, this was just changed to a mutex last week in commit b22d127a39dd 
("mempolicy: fix a race in shared_policy_replace()") so that sp_alloc() 
can be done with GFP_KERNEL, so I didn't consider reverting that behavior.  
Are you nacking that patch, which you acked, now?

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