diff -r 37fae02cc335 xen/common/page_alloc.c
--- a/xen/common/page_alloc.c	Fri Jul 25 15:03:03 2008 +0100
+++ b/xen/common/page_alloc.c	Mon Jul 28 16:02:40 2008 +0200
@@ -583,6 +583,13 @@
             init_heap_pages(pfn_dom_zone_type(i), mfn_to_page(i), 1);
     }
 
+    /* Reserve only up to 25% of node0's memory for DMA */
+    i = pfn_dom_zone_type(NODE_DATA(0)->node_spanned_pages / 4)
+                          + PAGE_SHIFT;
+    if ( i < dma_bitsize ) dma_bitsize = i;
+
+    ASSERT(dma_bitsize > PAGE_SHIFT + 1);
+
     printk("Domain heap initialised: DMA width %u bits\n", dma_bitsize);
 }
 #undef avail_for_domheap
diff -r 37fae02cc335 xen/include/asm-ia64/config.h
--- a/xen/include/asm-ia64/config.h	Fri Jul 25 15:03:03 2008 +0100
+++ b/xen/include/asm-ia64/config.h	Mon Jul 28 16:02:40 2008 +0200
@@ -44,7 +44,7 @@
 #define CONFIG_IOSAPIC
 #define supervisor_mode_kernel (0)
 
-#define CONFIG_DMA_BITSIZE 32
+#define CONFIG_DMA_BITSIZE 30
 
 #define PADDR_BITS	48
 
diff -r 37fae02cc335 xen/include/asm-x86/config.h
--- a/xen/include/asm-x86/config.h	Fri Jul 25 15:03:03 2008 +0100
+++ b/xen/include/asm-x86/config.h	Mon Jul 28 16:02:40 2008 +0200
@@ -97,7 +97,7 @@
 /* Primary stack is restricted to 8kB by guard pages. */
 #define PRIMARY_STACK_SIZE 8192
 
-#define CONFIG_DMA_BITSIZE 32
+#define CONFIG_DMA_BITSIZE 30
 
 #define BOOT_TRAMPOLINE 0x8c000
 #define bootsym_phys(sym)                                 \