---
 drivers/md/dm-exception-store.c |   52 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 46 insertions(+), 6 deletions(-)

Index: linux-2.6.26-fast/drivers/md/dm-exception-store.c
===================================================================
--- linux-2.6.26-fast.orig/drivers/md/dm-exception-store.c	2008-07-23 22:59:45.000000000 +0200
+++ linux-2.6.26-fast/drivers/md/dm-exception-store.c	2008-07-23 22:59:47.000000000 +0200
@@ -105,6 +105,11 @@ struct pstore {
 	void *area;
 
 	/*
+	 * One area containing just zeros, used to clear next area chunk.
+	 */
+	void *zero_area;
+
+	/*
 	 * Used to keep track of which metadata area the data in
 	 * 'chunk' refers to.
 	 */
@@ -149,6 +154,13 @@ static int alloc_area(struct pstore *ps)
 	if (!ps->area)
 		return r;
 
+	ps->zero_area = vmalloc(len);
+	if (!ps->zero_area) {
+		vfree(ps->area);
+		return r;
+	}
+	memset(ps->zero_area, 0, len);
+
 	return 0;
 }
 
@@ -156,6 +168,8 @@ static void free_area(struct pstore *ps)
 {
 	vfree(ps->area);
 	ps->area = NULL;
+	vfree(ps->zero_area);
+	ps->zero_area = NULL;
 }
 
 struct mdata_req {
@@ -235,10 +249,28 @@ static int area_io(struct pstore *ps, ch
 	return 0;
 }
 
-static int zero_area(struct pstore *ps, chunk_t area)
+static void zero_memory_area(struct pstore *ps, chunk_t area)
 {
 	memset(ps->area, 0, ps->snap->chunk_size << SECTOR_SHIFT);
-	return area_io(ps, area, WRITE);
+	ps->current_area = area;
+}
+
+static int zero_disk_area(struct pstore *ps, chunk_t area)
+{
+	struct dm_io_region where = {
+		.bdev = ps->snap->cow->bdev,
+		.sector = ps->snap->chunk_size * area_location(ps, area),
+		.count = ps->snap->chunk_size,
+	};
+	struct dm_io_request io_req = {
+		.bi_rw = WRITE,
+		.mem.type = DM_IO_VMA,
+		.mem.ptr.vma = ps->zero_area,
+		.client = ps->io_client,
+		.notify.fn = NULL,
+	};
+
+	return dm_io(&io_req, 1, &where, NULL);
 }
 
 static int read_header(struct pstore *ps, int *new_snapshot)
@@ -489,7 +521,8 @@ static int persistent_read_metadata(stru
 			return r;
 		}
 
-		r = zero_area(ps, 0);
+		zero_memory_area(ps, 0);
+		r = zero_disk_area(ps, 0);
 		if (r) {
 			DMWARN("zero_area(0) failed");
 			return r;
@@ -581,18 +614,25 @@ static void persistent_commit(struct exc
 	 */
 	if (atomic_dec_and_test(&ps->pending_count) ||
 	    (ps->current_committed == ps->exceptions_per_area)) {
+		if (ps->current_committed == ps->exceptions_per_area) {
+			r = zero_disk_area(ps, ps->current_area + 1);
+			if (r) {
+				ps->valid = 0;
+				goto skip_area_io;
+			}
+		}
+
 		r = area_io(ps, ps->current_area, WRITE);
 		if (r)
 			ps->valid = 0;
 
+skip_area_io:
 		/*
 		 * Have we completely filled the current area ?
 		 */
 		if (ps->current_committed == ps->exceptions_per_area) {
 			ps->current_committed = 0;
-			r = zero_area(ps, ps->current_area + 1);
-			if (r)
-				ps->valid = 0;
+			zero_memory_area(ps, ps->current_area + 1);
 		}
 
 		for (i = 0; i < ps->callback_count; i++) {