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Date:      Thu, 10 Nov 2011 17:04:33 +0000 (UTC)
From:      Alan Cox <alc@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org
Subject:   svn commit: r227422 - stable/8/sys/vm
Message-ID:  <201111101704.pAAH4XdQ048042@svn.freebsd.org>

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Author: alc
Date: Thu Nov 10 17:04:33 2011
New Revision: 227422
URL: http://svn.freebsd.org/changeset/base/227422

Log:
  MFC r226740
    Speed up vm_page_cache() and vm_page_remove() by checking for a few
    common cases that can be handled in constant time.

Modified:
  stable/8/sys/vm/vm_page.c
Directory Properties:
  stable/8/sys/   (props changed)
  stable/8/sys/amd64/include/xen/   (props changed)
  stable/8/sys/cddl/contrib/opensolaris/   (props changed)
  stable/8/sys/contrib/dev/acpica/   (props changed)
  stable/8/sys/contrib/pf/   (props changed)

Modified: stable/8/sys/vm/vm_page.c
==============================================================================
--- stable/8/sys/vm/vm_page.c	Thu Nov 10 17:01:34 2011	(r227421)
+++ stable/8/sys/vm/vm_page.c	Thu Nov 10 17:04:33 2011	(r227422)
@@ -737,7 +737,7 @@ void
 vm_page_remove(vm_page_t m)
 {
 	vm_object_t object;
-	vm_page_t root;
+	vm_page_t next, prev, root;
 
 	if ((object = m->object) == NULL)
 		return;
@@ -751,15 +751,42 @@ vm_page_remove(vm_page_t m)
 	/*
 	 * Now remove from the object's list of backed pages.
 	 */
-	if (m != object->root)
-		vm_page_splay(m->pindex, object->root);
-	if (m->left == NULL)
-		root = m->right;
-	else {
-		root = vm_page_splay(m->pindex, m->left);
-		root->right = m->right;
+	if ((next = TAILQ_NEXT(m, listq)) != NULL && next->left == m) {
+		/*
+		 * Since the page's successor in the list is also its parent
+		 * in the tree, its right subtree must be empty.
+		 */
+		next->left = m->left;
+		KASSERT(m->right == NULL,
+		    ("vm_page_remove: page %p has right child", m));
+	} else if ((prev = TAILQ_PREV(m, pglist, listq)) != NULL &&
+	    prev->right == m) {
+		/*
+		 * Since the page's predecessor in the list is also its parent
+		 * in the tree, its left subtree must be empty.
+		 */
+		KASSERT(m->left == NULL,
+		    ("vm_page_remove: page %p has left child", m));
+		prev->right = m->right;
+	} else {
+		if (m != object->root)
+			vm_page_splay(m->pindex, object->root);
+		if (m->left == NULL)
+			root = m->right;
+		else if (m->right == NULL)
+			root = m->left;
+		else {
+			/*
+			 * Move the page's successor to the root, because
+			 * pages are usually removed in ascending order.
+			 */
+			if (m->right != next)
+				vm_page_splay(m->pindex, m->right);
+			next->left = m->left;
+			root = next;
+		}
+		object->root = root;
 	}
-	object->root = root;
 	TAILQ_REMOVE(&object->memq, m, listq);
 
 	/*
@@ -1802,7 +1829,7 @@ void
 vm_page_cache(vm_page_t m)
 {
 	vm_object_t object;
-	vm_page_t root;
+	vm_page_t next, prev, root;
 
 	mtx_assert(&vm_page_queue_mtx, MA_OWNED);
 	object = m->object;
@@ -1838,15 +1865,42 @@ vm_page_cache(vm_page_t m)
 	 * Remove the page from the object's collection of resident
 	 * pages. 
 	 */
-	if (m != object->root)
-		vm_page_splay(m->pindex, object->root);
-	if (m->left == NULL)
-		root = m->right;
-	else {
-		root = vm_page_splay(m->pindex, m->left);
-		root->right = m->right;
+	if ((next = TAILQ_NEXT(m, listq)) != NULL && next->left == m) {
+		/*
+		 * Since the page's successor in the list is also its parent
+		 * in the tree, its right subtree must be empty.
+		 */
+		next->left = m->left;
+		KASSERT(m->right == NULL,
+		    ("vm_page_cache: page %p has right child", m));
+	} else if ((prev = TAILQ_PREV(m, pglist, listq)) != NULL &&
+	    prev->right == m) {
+		/*
+		 * Since the page's predecessor in the list is also its parent
+		 * in the tree, its left subtree must be empty.
+		 */
+		KASSERT(m->left == NULL,
+		    ("vm_page_cache: page %p has left child", m));
+		prev->right = m->right;
+	} else {
+		if (m != object->root)
+			vm_page_splay(m->pindex, object->root);
+		if (m->left == NULL)
+			root = m->right;
+		else if (m->right == NULL)
+			root = m->left;
+		else {
+			/*
+			 * Move the page's successor to the root, because
+			 * pages are usually removed in ascending order.
+			 */
+			if (m->right != next)
+				vm_page_splay(m->pindex, m->right);
+			next->left = m->left;
+			root = next;
+		}
+		object->root = root;
 	}
-	object->root = root;
 	TAILQ_REMOVE(&object->memq, m, listq);
 	object->resident_page_count--;
 



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