diff -Nuarp a/fs/buffer.c b/fs/buffer.c
--- a/fs/buffer.c	2010-10-13 17:42:06.472252298 +0200
+++ b/fs/buffer.c	2010-10-13 17:42:14.772244244 +0200
@@ -1687,8 +1687,9 @@ static int __block_write_full_page(struc
 			if (buffer_new(bh)) {
 				/* blockdev mappings never come here */
 				clear_buffer_new(bh);
-				unmap_underlying_metadata(bh->b_bdev,
-							bh->b_blocknr);
+				if (buffer_mapped(bh))
+					unmap_underlying_metadata(bh->b_bdev,
+								bh->b_blocknr);
 			}
 		}
 		bh = bh->b_this_page;
@@ -1873,7 +1874,8 @@ static int __block_prepare_write(struct
 			if (err)
 				break;
 			if (buffer_new(bh)) {
-				unmap_underlying_metadata(bh->b_bdev,
+				if (buffer_mapped(bh))
+					unmap_underlying_metadata(bh->b_bdev,
 							bh->b_blocknr);
 				if (PageUptodate(page)) {
 					clear_buffer_new(bh);
@@ -2592,7 +2594,7 @@ int nobh_write_begin_newtrunc(struct fil
 			goto failed;
 		if (!buffer_mapped(bh))
 			is_mapped_to_disk = 0;
-		if (buffer_new(bh))
+		if (buffer_new(bh) && buffer_mapped(bh))
 			unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
 		if (PageUptodate(page)) {
 			set_buffer_uptodate(bh);
diff -Nuarp a/fs/ext3/file.c b/fs/ext3/file.c
--- a/fs/ext3/file.c	2010-10-13 17:41:52.962541253 +0200
+++ b/fs/ext3/file.c	2010-10-13 17:42:25.083163556 +0200
@@ -52,6 +52,23 @@ static int ext3_release_file (struct ino
 	return 0;
 }

+static const struct vm_operations_struct ext3_file_vm_ops = {
+	.fault          = filemap_fault,
+	.page_mkwrite   = ext3_page_mkwrite,
+};
+
+static int ext3_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct address_space *mapping = file->f_mapping;
+
+	if (!mapping->a_ops->readpage)
+		return -ENOEXEC;
+	file_accessed(file);
+	vma->vm_ops = &ext3_file_vm_ops;
+	vma->vm_flags |= VM_CAN_NONLINEAR;
+	return 0;
+}
+
 const struct file_operations ext3_file_operations = {
 	.llseek		= generic_file_llseek,
 	.read		= do_sync_read,
@@ -62,7 +79,7 @@ const struct file_operations ext3_file_o
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= ext3_compat_ioctl,
 #endif
-	.mmap		= generic_file_mmap,
+	.mmap		= ext3_file_mmap,
 	.open		= dquot_file_open,
 	.release	= ext3_release_file,
 	.fsync		= ext3_sync_file,
diff -Nuarp a/fs/ext3/inode.c b/fs/ext3/inode.c
--- a/fs/ext3/inode.c	2010-10-13 17:41:42.722231144 +0200
+++ b/fs/ext3/inode.c	2010-10-13 17:41:12.973180756 +0200
@@ -38,6 +38,7 @@
 #include <linux/bio.h>
 #include <linux/fiemap.h>
 #include <linux/namei.h>
+#include <linux/mount.h>
 #include "xattr.h"
 #include "acl.h"

@@ -562,10 +563,17 @@ static int ext3_alloc_blocks(handle_t *h
 			count--;
 		}

-		if (count > 0)
+		if (index == indirect_blks)
 			break;
 	}

+	if (blks == 0) {
+		/* blks == 0 when allocating only indirect blocks */
+		new_blocks[index] = 0;
+		*err = 0;
+		return 0;
+	}
+
 	/* save the new block number for the first direct block */
 	new_blocks[index] = current_block;

@@ -676,7 +684,9 @@ failed:
 	for (i = 0; i <indirect_blks; i++)
 		ext3_free_blocks(handle, inode, new_blocks[i], 1);

-	ext3_free_blocks(handle, inode, new_blocks[i], num);
+	if (num > 0)
+		/* num == 0 when allocating only indirect blocks */
+		ext3_free_blocks(handle, inode, new_blocks[i], num);

 	return err;
 }
@@ -735,7 +745,8 @@ static int ext3_splice_branch(handle_t *
 	 * in i_block_alloc_info, to assist find the proper goal block for next
 	 * allocation
 	 */
-	if (block_i) {
+	if (block_i && blks > 0) {
+		/* blks == 0 when allocating only indirect blocks */
 		block_i->last_alloc_logical_block = block + blks - 1;
 		block_i->last_alloc_physical_block =
 				le32_to_cpu(where[num].key) + blks - 1;
@@ -778,7 +789,9 @@ err_out:
 		ext3_journal_forget(handle, where[i].bh);
 		ext3_free_blocks(handle,inode,le32_to_cpu(where[i-1].key),1);
 	}
-	ext3_free_blocks(handle, inode, le32_to_cpu(where[num].key), blks);
+	if (blks > 0)
+		/* blks == 0 when allocating only indirect blocks */
+		ext3_free_blocks(handle, inode, le32_to_cpu(where[num].key), blks);

 	return err;
 }
@@ -905,6 +918,11 @@ int ext3_get_blocks_handle(handle_t *han

 	/* the number of blocks need to allocate for [d,t]indirect blocks */
 	indirect_blks = (chain + depth) - partial - 1;
+	if (indirect_blks + maxblocks == 0) {
+		/* maxblocks == 0 when allocating only indirect blocks */
+		mutex_unlock(&ei->truncate_mutex);
+		goto cleanup;
+	}

 	/*
 	 * Next look up the indirect map to count the totoal number of
@@ -929,7 +947,8 @@ int ext3_get_blocks_handle(handle_t *han
 		err = ext3_splice_branch(handle, inode, iblock,
 					partial, indirect_blks, count);
 	mutex_unlock(&ei->truncate_mutex);
-	if (err)
+	if (err || count == 0)
+		/* count == 0 when allocating only indirect blocks */
 		goto cleanup;

 	set_buffer_new(bh_result);
@@ -981,6 +1000,9 @@ static int ext3_get_block(struct inode *
 		started = 1;
 	}

+	if (create < 0)
+		/* create < 0 when allocating only indirect blocks */
+		max_blocks = 0;
 	ret = ext3_get_blocks_handle(handle, inode, iblock,
 					max_blocks, bh_result, create);
 	if (ret > 0) {
@@ -1827,6 +1849,43 @@ out:
 }

 /*
+ * Reserve block writes instead of allocation. Called only on buffer heads
+ * attached to a page (and thus for 1 block).
+ */
+static int ext3_da_get_block(struct inode *inode, sector_t iblock,
+		struct buffer_head *bh, int create)
+{
+	int ret;
+
+	/* Buffer has already blocks reserved? */
+	if (buffer_delay(bh))
+		return 0;
+
+	/* passing -1 to allocate only indirect blocks */
+	ret = ext3_get_block(inode, iblock, bh, -1);
+	if (ret < 0)
+		return ret;
+	if (ret > 0 || !create)
+		return 0;
+	set_buffer_delay(bh);
+	set_buffer_new(bh);
+	return 0;
+}
+
+int ext3_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	int retry = 0;
+	int ret;
+	struct super_block *sb = vma->vm_file->f_path.mnt->mnt_sb;
+
+	do {
+		ret = block_page_mkwrite(vma, vmf, ext3_da_get_block);
+	} while (ret == VM_FAULT_SIGBUS &&
+			ext3_should_retry_alloc(sb, &retry));
+	return ret;
+}
+
+/*
  * Pages can be marked dirty completely asynchronously from ext3's journalling
  * activity.  By filemap_sync_pte(), try_to_unmap_one(), etc.  We cannot do
  * much here because ->set_page_dirty is called under VFS locks.  The page is
diff -Nuarp a/include/linux/ext3_fs.h b/include/linux/ext3_fs.h
--- a/include/linux/ext3_fs.h	2010-10-13 17:49:26.892439258 +0200
+++ b/include/linux/ext3_fs.h	2010-10-13 17:49:10.662493115 +0200
@@ -909,6 +909,7 @@ extern void ext3_get_inode_flags(struct
 extern void ext3_set_aops(struct inode *inode);
 extern int ext3_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		       u64 start, u64 len);
+extern int ext3_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);

 /* ioctl.c */
 extern long ext3_ioctl(struct file *, unsigned int, unsigned long);