--- dbinc/mp.h.orig	2006-09-07 14:31:58.000000000 -0700
+++ dbinc/mp.h	2007-01-06 19:14:56.000000000 -0800
@@ -378,6 +378,23 @@
 #define	BH_FREE_REUSE		0x02
 #define	BH_FREE_UNLOCKED	0x04
 
+#ifdef DIAG_MVCC
+#define	BH_ALIGNED
+#define VM_PAGESIZE 4096
+#endif
+
+/* Linux O_DIRECT needs aligned buffers. 2.6 kernel allows 512 byte
+ * alignment, otherwise need page sized (4096).
+ */
+#if defined(linux) && !defined(BH_ALIGNED)
+#define	BH_ALIGNED
+#ifdef LINUX_NEEDS_PAGE_ALIGNMENT
+#define VM_PAGESIZE 4096
+#else	/* Linux 2.6+ */
+#define VM_PAGESIZE 512
+#endif
+#endif
+
 /*
  * BH --
  *	Buffer header.
@@ -404,7 +421,7 @@
 
 	roff_t		td_off;		/* MVCC: creating TXN_DETAIL offset. */
 	SH_CHAIN_ENTRY	vc;		/* MVCC: version chain. */
-#ifdef DIAG_MVCC
+#ifdef BH_ALIGNED
 	u_int16_t	align_off;	/* Alignment offset for diagnostics.*/
 #endif
 
@@ -465,15 +482,14 @@
     (dbc->txn != NULL && F_ISSET(dbc->txn, TXN_SNAPSHOT) &&		\
     dbc->txn->td != NULL && __memp_skip_curadj(dbc, pgno))
 
-#if defined(DIAG_MVCC) && defined(HAVE_MPROTECT)
-#define	VM_PAGESIZE 4096
-#define	MVCC_BHSIZE(mfp, sz) do {					\
+#ifdef BH_ALIGNED
+#define	BHSIZE(mfp, sz) do {					\
 	sz += VM_PAGESIZE + sizeof(BH);					\
 	if (mfp->stat.st_pagesize < VM_PAGESIZE)			\
 		sz += VM_PAGESIZE - mfp->stat.st_pagesize;		\
 } while (0)
 
-#define	MVCC_BHALIGN(mfp, p) do {					\
+#define	BHALIGN(mfp, p) do {					\
 	if (mfp != NULL) {						\
 		BH *__bhp;						\
 		void *__orig = (p);					\
@@ -493,13 +509,19 @@
 	}								\
 } while (0)
 
-#define	MVCC_BHUNALIGN(mfp, p) do {					\
+#define	BHUNALIGN(mfp, p) do {					\
 	if ((mfp) != NULL) {						\
 		BH *bhp = (BH *)(p);					\
 		(p) = ((u_int8_t *)bhp - bhp->align_off);		\
 	}								\
 } while (0)
+#else
+#define	BHSIZE(mfp, sz) do {} while (0)
+#define	BHALIGN(mfp, p) do {} while (0)
+#define	BHUNALIGN(mfp, p) do {} while (0)
+#endif
 
+#if defined(DIAG_MVCC) && defined(HAVE_MPROTECT)
 #ifdef linux
 #define	MVCC_MPROTECT(buf, sz, mode) do {				\
 	int __ret = mprotect((buf), (sz), (mode));			\
@@ -513,11 +535,7 @@
 	}								\
 } while (0)
 #endif /* linux */
-
-#else /* defined(DIAG_MVCC) && defined(HAVE_MPROTECT) */
-#define	MVCC_BHSIZE(mfp, sz) do {} while (0)
-#define	MVCC_BHALIGN(mfp, p) do {} while (0)
-#define	MVCC_BHUNALIGN(mfp, p) do {} while (0)
+#else
 #define	MVCC_MPROTECT(buf, size, mode) do {} while (0)
 #endif
 
--- mp/mp_alloc.c.orig	2006-09-07 14:32:03.000000000 -0700
+++ mp/mp_alloc.c	2007-01-06 19:14:56.000000000 -0800
@@ -66,7 +66,7 @@
 	if (mfp != NULL) {
 		len = SSZA(BH, buf) + mfp->stat.st_pagesize;
 		/* Add space for alignment padding for MVCC diagnostics. */
-		MVCC_BHSIZE(mfp, len);
+		BHSIZE(mfp, len);
 	}
 
 	MPOOL_REGION_LOCK(dbenv, infop);
@@ -91,10 +91,10 @@
 			c_mp->stat.st_pages++;
 		MPOOL_REGION_UNLOCK(dbenv, infop);
 		/*
-		 * For MVCC diagnostics, align the pointer so that the buffer
+		 * If necessary, align the pointer so that the buffer
 		 * starts on a page boundary.
 		 */
-		MVCC_BHALIGN(mfp, p);
+		BHALIGN(mfp, p);
 
 found:		if (offsetp != NULL)
 			*offsetp = R_OFFSET(infop, p);
@@ -447,7 +447,7 @@
 	MPOOLFILE *mfp;
 	void *buf;
 {
-	MVCC_BHUNALIGN(mfp, buf);
+	BHUNALIGN(mfp, buf);
 	COMPQUIET(mfp, NULL);
 	__db_shalloc_free(infop, buf);
 }
--- mp/mp_fget.c.orig	2006-09-13 09:22:42.000000000 -0700
+++ mp/mp_fget.c	2007-01-06 19:14:56.000000000 -0800
@@ -708,7 +708,7 @@
 		 * the hash bucket's priority.
 		 */
 		/*lint --e{668} (flexelint: bhp cannot be NULL). */
-#ifdef DIAG_MVCC
+#ifdef BH_ALIGNED
 		memset(bhp, 0, SSZ(BH, align_off));
 #else
 		memset(bhp, 0, sizeof(BH));