ext4: use ext4_get_block_write in buffer write

Allocate uninitialized extent before ext4 buffer write and
convert the extent to initialized after io completes.
The purpose is to make sure an extent can only be marked
initialized after it has been written with new data so
we can safely drop the i_mutex lock in ext4 DIO read without
exposing stale data. This helps to improve multi-thread DIO
read performance on high-speed disks.

Skip the nobh and data=journal mount cases to make things simple for now.

Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 12 insertions, 10 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 90ba8d9df69..c7f166ab50e 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1619,7 +1619,7 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
         BUG_ON(path[depth].p_hdr == NULL);
 
         /* try to insert block into found extent and return */
-        if (ex && (flag != EXT4_GET_BLOCKS_PRE_IO)
+        if (ex && !(flag & EXT4_GET_BLOCKS_PRE_IO)
                 && ext4_can_extents_be_merged(inode, ex, newext)) {
                 ext_debug("append [%d]%d block to %d:[%d]%d (from %llu)\n",
                                 ext4_ext_is_uninitialized(newext),
@@ -1740,7 +1740,7 @@ has_space:
 
 merge:
         /* try to merge extents to the right */
-        if (flag != EXT4_GET_BLOCKS_PRE_IO)
+        if (!(flag & EXT4_GET_BLOCKS_PRE_IO))
                 ext4_ext_try_to_merge(inode, path, nearex);
 
         /* try to merge extents to the left */
@@ -3065,7 +3065,7 @@ ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
         ext4_ext_show_leaf(inode, path);
 
         /* get_block() before submit the IO, split the extent */
-        if (flags == EXT4_GET_BLOCKS_PRE_IO) {
+        if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
                 ret = ext4_split_unwritten_extents(handle,
                                                 inode, path, iblock,
                                                 max_blocks, flags);
@@ -3078,10 +3078,12 @@ ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
                         io->flag = EXT4_IO_UNWRITTEN;
                 else
                         ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
+                if (ext4_should_dioread_nolock(inode))
+                        set_buffer_uninit(bh_result);
                 goto out;
         }
         /* IO end_io complete, convert the filled extent to written */
-        if (flags == EXT4_GET_BLOCKS_CONVERT) {
+        if ((flags & EXT4_GET_BLOCKS_CONVERT)) {
                 ret = ext4_convert_unwritten_extents_endio(handle, inode,
                                                         path);
                 if (ret >= 0)
@@ -3351,21 +3353,21 @@ int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
         if (flags & EXT4_GET_BLOCKS_UNINIT_EXT){
                 ext4_ext_mark_uninitialized(&newex);
                 /*
-                 * io_end structure was created for every async
-                 * direct IO write to the middle of the file.
-                 * To avoid unecessary convertion for every aio dio rewrite
-                 * to the mid of file, here we flag the IO that is really
-                 * need the convertion.
+                 * io_end structure was created for every IO write to an
+                 * uninitialized extent. To avoid unecessary conversion,
+                 * here we flag the IO that really needs the conversion.
                  * For non asycn direct IO case, flag the inode state
                  * that we need to perform convertion when IO is done.
                  */
-                if (flags == EXT4_GET_BLOCKS_PRE_IO) {
+                if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
                         if (io)
                                 io->flag = EXT4_IO_UNWRITTEN;
                         else
                                 ext4_set_inode_state(inode,
                                                      EXT4_STATE_DIO_UNWRITTEN);
                 }
+                if (ext4_should_dioread_nolock(inode))
+                        set_buffer_uninit(bh_result);
         }
 
         if (unlikely(EXT4_I(inode)->i_flags & EXT4_EOFBLOCKS_FL)) {