linux-kernel - [Patch] rcu: remove dead code in include/linux/pagemap.h

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Date:	Mon, 31 Jan 2011 14:27:04 +0800
From:	Amerigo Wang <amwang@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	WANG Cong <amwang@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>
Subject: [Patch] rcu: remove dead code in include/linux/pagemap.h

TREE_RCU depends on !PREEMPT && SMP, when !CONFIG_SMP is true, CONFIG_TREE_RCU
will be false, thus "!defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)"
is always false.

Remove these dead code.

Signed-off-by: WANG Cong <amwang@...hat.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

---
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 9c66e99..e2bbbe3 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -133,23 +133,6 @@ static inline int page_cache_get_speculative(struct page *page)
 {
 	VM_BUG_ON(in_interrupt());
 
-#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
-# ifdef CONFIG_PREEMPT
-	VM_BUG_ON(!in_atomic());
-# endif
-	/*
-	 * Preempt must be disabled here - we rely on rcu_read_lock doing
-	 * this for us.
-	 *
-	 * Pagecache won't be truncated from interrupt context, so if we have
-	 * found a page in the radix tree here, we have pinned its refcount by
-	 * disabling preempt, and hence no need for the "speculative get" that
-	 * SMP requires.
-	 */
-	VM_BUG_ON(page_count(page) == 0);
-	atomic_inc(&page->_count);
-
-#else
 	if (unlikely(!get_page_unless_zero(page))) {
 		/*
 		 * Either the page has been freed, or will be freed.
@@ -158,7 +141,6 @@ static inline int page_cache_get_speculative(struct page *page)
 		 */
 		return 0;
 	}
-#endif
 	VM_BUG_ON(PageTail(page));
 
 	return 1;
@@ -171,17 +153,9 @@ static inline int page_cache_add_speculative(struct page *page, int count)
 {
 	VM_BUG_ON(in_interrupt());
 
-#if !defined(CONFIG_SMP) && defined(CONFIG_TREE_RCU)
-# ifdef CONFIG_PREEMPT
-	VM_BUG_ON(!in_atomic());
-# endif
-	VM_BUG_ON(page_count(page) == 0);
-	atomic_add(count, &page->_count);
-
-#else
 	if (unlikely(!atomic_add_unless(&page->_count, count, 0)))
 		return 0;
-#endif
+
 	VM_BUG_ON(PageCompound(page) && page != compound_head(page));
 
 	return 1;
--
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