On Wed, Oct 17, 2012 at 3:50 PM, David Rientjes <rientjes@xxxxxxxxxx> wrote:
> On Wed, 17 Oct 2012, KOSAKI Motohiro wrote:
>
>> > 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?
Yes, sadly. /proc usage is a corner case issue. It's not worth to
strike main path.
see commit 52cd3b0740 and around patches. That explain why we avoided your
approach.
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