[PATCH v2 5/7] ext4: Add support for FALLOC_FL_PROVISION

[Sarthak Kukreti <sarthakkukreti@chromium.org>]

Once ext4 is done mapping blocks for an fallocate() request, send
out an FALLOC_FL_PROVISION request to the underlying layer to
ensure that the space is provisioned for the newly allocated extent
or indirect blocks.

There is an expected performance degradation with fallocate() calls made
with this flag due to the extra REQ_OP_PROVISIONs sent to the underlying
storage.

Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
---
 fs/ext4/ext4.h         |  2 ++
 fs/ext4/extents.c      | 15 ++++++++++++++-
 fs/ext4/indirect.c     |  9 +++++++++
 include/linux/blkdev.h | 11 +++++++++++
 4 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 140e1eb300d1..49832e90b62f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -673,6 +673,8 @@ enum {
 #define EXT4_GET_BLOCKS_IO_SUBMIT		0x0400
 	/* Caller is in the atomic contex, find extent if it has been cached */
 #define EXT4_GET_BLOCKS_CACHED_NOWAIT		0x0800
+	/* Provision blocks on underlying storage */
+#define EXT4_GET_BLOCKS_PROVISION		0x1000
 
 /*
  * The bit position of these flags must not overlap with any of the
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 9de1c9d1a13d..2e64a9211792 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4361,6 +4361,13 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 		}
 	}
 
+	/* Attempt to provision blocks on underlying storage */
+	if (flags & EXT4_GET_BLOCKS_PROVISION) {
+		err = sb_issue_provision(inode->i_sb, pblk, ar.len, GFP_NOFS);
+		if (err)
+			goto out;
+	}
+
 	/*
 	 * Cache the extent and update transaction to commit on fdatasync only
 	 * when it is _not_ an unwritten extent.
@@ -4694,7 +4701,7 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	/* Return error if mode is not supported */
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
 		     FALLOC_FL_COLLAPSE_RANGE | FALLOC_FL_ZERO_RANGE |
-		     FALLOC_FL_INSERT_RANGE))
+		     FALLOC_FL_INSERT_RANGE | FALLOC_FL_PROVISION))
 		return -EOPNOTSUPP;
 
 	inode_lock(inode);
@@ -4754,6 +4761,12 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	if (ret)
 		goto out;
 
+	/* Ensure that preallocation provisions the blocks on the underlying
+	 * storage device.
+	 */
+	if (mode & FALLOC_FL_PROVISION)
+		flags |= EXT4_GET_BLOCKS_PROVISION;
+
 	ret = ext4_alloc_file_blocks(file, lblk, max_blocks, new_size, flags);
 	if (ret)
 		goto out;
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index c68bebe7ff4b..a8065aae7563 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -647,6 +647,15 @@ int ext4_ind_map_blocks(handle_t *handle, struct inode *inode,
 	if (err)
 		goto cleanup;
 
+	/* Attempt to provision blocks on underlying storage */
+	if (flags & EXT4_GET_BLOCKS_PROVISION) {
+		err = sb_issue_provision(inode->i_sb,
+					 le32_to_cpu(chain[depth-1].key),
+					 ar.len, GFP_NOFS);
+		if (err)
+			goto out;
+	}
+
 	map->m_flags |= EXT4_MAP_NEW;
 
 	ext4_update_inode_fsync_trans(handle, inode, 1);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index f1abc7b43e25..b2e3244e9f3d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1093,6 +1093,17 @@ static inline int sb_issue_zeroout(struct super_block *sb, sector_t block,
 				    gfp_mask, 0);
 }
 
+static inline int sb_issue_provision(struct super_block *sb, sector_t block,
+		sector_t nr_blocks, gfp_t gfp_mask)
+{
+	return blkdev_issue_provision(sb->s_bdev,
+				      block << (sb->s_blocksize_bits -
+					      SECTOR_SHIFT),
+				      nr_blocks << (sb->s_blocksize_bits -
+						    SECTOR_SHIFT),
+				      gfp_mask);
+}
+
 static inline bool bdev_is_partition(struct block_device *bdev)
 {
 	return bdev->bd_partno;
-- 
2.37.3