linux-kernel - [185/264] sparc: gup_pte_range() support THP based tail recounting

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Date:	Wed, 09 Nov 2011 13:33:52 -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>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	David Miller <davem@...emloft.net>
Subject: [185/264] sparc: gup_pte_range() support THP based tail recounting

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

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

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

commit e0d85a366c2300efd230ef82a9b22110b0658331 upstream.

Up to this point the code assumed old refcounting for hugepages (pre-thp).
 This updates the code directly to the thp mapcount tail page refcounting.

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>
Cc: David Gibson <david@...son.dropbear.id.au>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Acked-by: David Miller <davem@...emloft.net>
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/sparc/mm/gup.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/arch/sparc/mm/gup.c
+++ b/arch/sparc/mm/gup.c
@@ -12,6 +12,17 @@
 #include <linux/rwsem.h>
 #include <asm/pgtable.h>
 
+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
@@ -56,6 +67,8 @@ static noinline int gup_pte_range(pmd_t
 			put_page(head);
 			return 0;
 		}
+		if (head != page)
+			get_huge_page_tail(page);
 
 		pages[*nr] = page;
 		(*nr)++;


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