linux-kernel - Re: [patch for-3.7] mm, mempolicy: fix printing stack contents in numa

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Date:	Wed, 17 Oct 2012 12:50:21 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
cc:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	bhutchings@...arflare.com,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch for-3.7] mm, mempolicy: fix printing stack contents in
 numa_maps

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?
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