ext4: Convert truncate_mutex to read write semaphore.

We are currently taking the truncate_mutex for every read. This would have
performance impact on large CPU configuration. Convert the lock to read write
semaphore and take read lock when we are trying to read the file.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index ec5019fa552f..03d1bbb78a2f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -1565,7 +1565,7 @@ static int ext4_ext_rm_idx(handle_t *handle, struct inode *inode,
  * This routine returns max. credits that the extent tree can consume.
  * It should be OK for low-performance paths like ->writepage()
  * To allow many writing processes to fit into a single transaction,
- * the caller should calculate credits under truncate_mutex and
+ * the caller should calculate credits under i_data_sem and
  * pass the actual path.
  */
 int ext4_ext_calc_credits_for_insert(struct inode *inode,
@@ -2131,7 +2131,8 @@ out:
 
 /*
  * Need to be called with
- * mutex_lock(&EXT4_I(inode)->truncate_mutex);
+ * down_read(&EXT4_I(inode)->i_data_sem) if not allocating file system block
+ * (ie, create is zero). Otherwise down_write(&EXT4_I(inode)->i_data_sem)
  */
 int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
                         ext4_lblk_t iblock,
@@ -2350,7 +2351,7 @@ void ext4_ext_truncate(struct inode * inode, struct page *page)
         if (page)
                 ext4_block_truncate_page(handle, page, mapping, inode->i_size);
 
-        mutex_lock(&EXT4_I(inode)->truncate_mutex);
+        down_write(&EXT4_I(inode)->i_data_sem);
         ext4_ext_invalidate_cache(inode);
 
         /*
@@ -2386,7 +2387,7 @@ out_stop:
         if (inode->i_nlink)
                 ext4_orphan_del(handle, inode);
 
-        mutex_unlock(&EXT4_I(inode)->truncate_mutex);
+        up_write(&EXT4_I(inode)->i_data_sem);
         ext4_journal_stop(handle);
 }
 
@@ -2450,7 +2451,7 @@ long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
          * modify 1 super block, 1 block bitmap and 1 group descriptor.
          */
         credits = EXT4_DATA_TRANS_BLOCKS(inode->i_sb) + 3;
-        mutex_lock(&EXT4_I(inode)->truncate_mutex)
+        down_write((&EXT4_I(inode)->i_data_sem));
 retry:
         while (ret >= 0 && ret < max_blocks) {
                 block = block + ret;
@@ -2507,7 +2508,7 @@ retry:
         if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                 goto retry;
 
-        mutex_unlock(&EXT4_I(inode)->truncate_mutex)
+        up_write((&EXT4_I(inode)->i_data_sem));
         /*
          * Time to update the file size.
          * Update only when preallocation was requested beyond the file size.