--- a/usr/src/lib/libzpool/common/sys/zfs_context.h	Wed Aug 18 15:20:51 2010 -0400
+++ b/usr/src/lib/libzpool/common/sys/zfs_context.h	Wed Aug 18 12:47:36 2010 -0700
@@ -315,6 +315,7 @@
 #define	KM_PUSHPAGE		KM_SLEEP
 #define	KM_NOSLEEP		UMEM_DEFAULT
 #define	KMC_NODEBUG		UMC_NODEBUG
+#define	KMC_NOTOUCH		0	/* not needed for userland caches */
 #define	kmem_alloc(_s, _f)	umem_alloc(_s, _f)
 #define	kmem_zalloc(_s, _f)	umem_zalloc(_s, _f)
 #define	kmem_free(_b, _s)	umem_free(_b, _s)

--- a/usr/src/uts/common/fs/zfs/zio.c	Wed Aug 18 15:20:51 2010 -0400
+++ b/usr/src/uts/common/fs/zfs/zio.c	Wed Aug 18 12:47:36 2010 -0700
@@ -117,6 +117,7 @@
 		size_t size = (c + 1) << SPA_MINBLOCKSHIFT;
 		size_t p2 = size;
 		size_t align = 0;
+		size_t cflags = (size > zio_buf_debug_limit) ? KMC_NODEBUG : 0;
 
 		while (p2 & (p2 - 1))
 			p2 &= p2 - 1;
@@ -133,13 +134,17 @@
 			char name[36];
 			(void) sprintf(name, "zio_buf_%lu", (ulong_t)size);
 			zio_buf_cache[c] = kmem_cache_create(name, size,
-			    align, NULL, NULL, NULL, NULL, NULL,
-			    size > zio_buf_debug_limit ? KMC_NODEBUG : 0);
-
+			    align, NULL, NULL, NULL, NULL, NULL, cflags);
+
+			/*
+			 * Since zio_data bufs do not appear in crash dumps, we
+			 * pass KMC_NOTOUCH so that no allocator metadata is
+			 * stored with the buffers.
+			 */
 			(void) sprintf(name, "zio_data_buf_%lu", (ulong_t)size);
 			zio_data_buf_cache[c] = kmem_cache_create(name, size,
 			    align, NULL, NULL, NULL, NULL, data_alloc_arena,
-			    size > zio_buf_debug_limit ? KMC_NODEBUG : 0);
+			    cflags | KMC_NOTOUCH);
 		}
 	}
 

--- a/usr/src/uts/common/vm/seg_kmem.c	Wed Aug 18 15:20:51 2010 -0400
+++ b/usr/src/uts/common/vm/seg_kmem.c	Wed Aug 18 12:47:36 2010 -0700
@@ -1519,8 +1519,13 @@
 	ASSERT(zio_mem_base != NULL);
 	ASSERT(zio_mem_size != 0);
 
+	/*
+	 * To reduce VA space fragmentation, we set up quantum caches for the
+	 * smaller sizes;  we chose 32k because that translates to 128k VA
+	 * slabs, which matches nicely with the common 128k zio_data bufs.
+	 */
 	zio_arena = vmem_create("zfs_file_data", zio_mem_base, zio_mem_size,
-	    PAGESIZE, NULL, NULL, NULL, 0, VM_SLEEP);
+	    PAGESIZE, NULL, NULL, NULL, 32 * 1024, VM_SLEEP);
 
 	zio_alloc_arena = vmem_create("zfs_file_data_buf", NULL, 0, PAGESIZE,
 	    segkmem_zio_alloc, segkmem_zio_free, zio_arena, 0, VM_SLEEP);