linux-kernel - Re: [patch for-3.6] mm, thp: fix mapped pages avoiding unevictable list on mlock

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Date:	Wed, 26 Sep 2012 18:40:04 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michel Lespinasse <walken@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	stable@...r.kernel.org
Subject: Re: [patch for-3.6] mm, thp: fix mapped pages avoiding unevictable
 list on mlock

On Wed, 19 Sep 2012, Hugh Dickins wrote:

> Good catch, and the patch looks right to me, as far as it goes:
> but does it go far enough?
> 
> I hesitate because it looks as if the NR_MLOCK zone page state is
> maintained (with incs and decs) in ignorance of THP; so although
> you will be correcting the Unevictable kB with your mlock_vma_page(),
> the Mlocked kB just above it in /proc/meminfo would still be wrong?
> 

Indeed, NR_MLOCK is a separate problem with regard to thp and it's 
currently incremented once for every hugepage rather than HPAGE_PMD_NR.  
mlock_vma_page() needs to increment by hpage_nr_pages(page) like 
add_page_to_lru_list() does.

> I suppose I'm not sure whether this is material for late-3.6:
> surely it's not a fix for a recent regression?
> 

Ok, sounds good.  If there's no objection, I'd like to ask Andrew to apply 
this to -mm and remove the cc to stable@...r.kernel.org since the 
mlock_vma_page() problem above is separate and doesn't conflict with this 
code, so I'll send a followup patch to address that.

Thanks!
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