linux-kernel - [178/264] powerpc: remove superfluous PageTail checks on the pte gup

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Message-Id: <20111109213200.120966532@clark.kroah.org>
Date:	Wed, 09 Nov 2011 13:33:45 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Andrea Arcangeli <aarcange@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Hugh Dickins <hughd@...gle.com>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Gibson <david@...son.dropbear.id.au>
Subject: [178/264] powerpc: remove superfluous PageTail checks on the pte gup_fast

3.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrea Arcangeli <aarcange@...hat.com>

commit 2839bdc1bfc0af76a2f0f11eca011590520a04fa upstream.

This part of gup_fast doesn't seem capable of handling hugetlbfs ptes,
those should be handled by gup_hugepd only, so these checks are
superfluous.

Plus if this wasn't a noop, it would have oopsed because, the insistence
of using the speculative refcounting would trigger a VM_BUG_ON if a tail
page was encountered in the page_cache_get_speculative().

Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Johannes Weiner <jweiner@...hat.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Acked-by: David Gibson <david@...son.dropbear.id.au>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 arch/powerpc/mm/gup.c |   13 -------------
 1 file changed, 13 deletions(-)

--- a/arch/powerpc/mm/gup.c
+++ b/arch/powerpc/mm/gup.c
@@ -16,17 +16,6 @@
 
 #ifdef __HAVE_ARCH_PTE_SPECIAL
 
-static inline void get_huge_page_tail(struct page *page)
-{
-	/*
-	 * __split_huge_page_refcount() cannot run
-	 * from under us.
-	 */
-	VM_BUG_ON(page_mapcount(page) < 0);
-	VM_BUG_ON(atomic_read(&page->_count) != 0);
-	atomic_inc(&page->_mapcount);
-}
-
 /*
  * The performance critical leaf functions are made noinline otherwise gcc
  * inlines everything into a single function which results in too much
@@ -58,8 +47,6 @@ static noinline int gup_pte_range(pmd_t
 			put_page(page);
 			return 0;
 		}
-		if (PageTail(page))
-			get_huge_page_tail(page);
 		pages[*nr] = page;
 		(*nr)++;
 


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