svn commit: r228312 - user/attilio/vmcontention/sys/vm

[Attilio Rao]

Author: attilio
Date: Tue Dec  6 19:04:45 2011
New Revision: 228312
URL: http://svn.freebsd.org/changeset/base/228312

Log:
  - Make rn_count 32-bits as it will naturally pad for 32-bit arches
  - Avoid to use atomic to manipulate it at level0 because it seems
    unneeded and introduces a bug on big-endian architectures where only
    the top half (2 bits) of the double-words are written (as sparc64,
    for example, doesn't support atomics at 16-bits) heading to a wrong
    handling of rn_count.
  
  Reported by:	flo, andreast
  Found by:	marius
  No answer by:	jeff

Modified:
  user/attilio/vmcontention/sys/vm/vm_radix.c
  user/attilio/vmcontention/sys/vm/vm_radix.h

Modified: user/attilio/vmcontention/sys/vm/vm_radix.c
==============================================================================
--- user/attilio/vmcontention/sys/vm/vm_radix.c	Tue Dec  6 18:01:09 2011	(r228311)
+++ user/attilio/vmcontention/sys/vm/vm_radix.c	Tue Dec  6 19:04:45 2011	(r228312)
@@ -344,7 +344,7 @@ vm_radix_insert(struct vm_radix *rtree, 
 	    rnode->rn_child[slot], (u_long)index));
 	val = (void *)((uintptr_t)val | VM_RADIX_BLACK);
 	rnode->rn_child[slot] = val;
-	atomic_add_int((volatile int *)&rnode->rn_count, 1);
+	rnode->rn_count++;
 	CTR6(KTR_VM,
 	    "insert: tree %p, index %ju, level %d, slot %d, rnode %p, count %u",
 	    rtree, (uintmax_t)index, level, slot, rnode, rnode->rn_count);
@@ -681,14 +681,7 @@ vm_radix_remove(struct vm_radix *rtree, 
 		    (rnode != NULL) ? rnode->rn_child[slot] : NULL,
 		    (rnode != NULL) ? rnode->rn_count : 0);
 		rnode->rn_child[slot] = NULL;
-		/*
-		 * Use atomics for the last level since red and black
-		 * will both adjust it.
-		 */
-		if (level == 0)
-			atomic_add_int((volatile int *)&rnode->rn_count, -1);
-		else
-			rnode->rn_count--;
+		rnode->rn_count--;
 		/*
 		 * Only allow black removes to prune the tree.
 		 */

Modified: user/attilio/vmcontention/sys/vm/vm_radix.h
==============================================================================
--- user/attilio/vmcontention/sys/vm/vm_radix.h	Tue Dec  6 18:01:09 2011	(r228311)
+++ user/attilio/vmcontention/sys/vm/vm_radix.h	Tue Dec  6 19:04:45 2011	(r228312)
@@ -61,8 +61,8 @@ struct vm_radix {
 CTASSERT(VM_RADIX_HEIGHT >= VM_RADIX_LIMIT);
 
 struct vm_radix_node {
-	void	*rn_child[VM_RADIX_COUNT];	/* Child nodes. */
-    	volatile uint16_t rn_count;		/* Valid children. */
+	void		*rn_child[VM_RADIX_COUNT];	/* Child nodes. */
+    	uint32_t	 rn_count;			/* Valid children. */
 };
 
 void	vm_radix_init(void);