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>

2 files changed, 7 insertions, 24 deletions

diff --git a/include/linux/ext4_fs.h b/include/linux/ext4_fs.h
index 583049c1d366..300cc5a5adb9 100644
--- a/include/linux/ext4_fs.h
+++ b/include/linux/ext4_fs.h
@@ -1107,27 +1107,10 @@ extern void ext4_ext_init(struct super_block *);
 extern void ext4_ext_release(struct super_block *);
 extern long ext4_fallocate(struct inode *inode, int mode, loff_t offset,
                           loff_t len);
-static inline int
-ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
-                        unsigned long max_blocks, struct buffer_head *bh,
-                        int create, int extend_disksize)
-{
-        int retval;
-        mutex_lock(&EXT4_I(inode)->truncate_mutex);
-        if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
-                retval = ext4_ext_get_blocks(handle, inode,
-                                                (ext4_lblk_t)block, max_blocks,
-                                                bh, create, extend_disksize);
-        } else {
-                retval = ext4_get_blocks_handle(handle, inode,
-                                                (ext4_lblk_t)block, max_blocks,
-                                                bh, create, extend_disksize);
-        }
-        mutex_unlock(&EXT4_I(inode)->truncate_mutex);
-        return retval;
-}
-
-
+extern int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode,
+                        sector_t block, unsigned long max_blocks,
+                        struct buffer_head *bh, int create,
+                        int extend_disksize);
 #endif  /* __KERNEL__ */
 
 #endif  /* _LINUX_EXT4_FS_H */
diff --git a/include/linux/ext4_fs_i.h b/include/linux/ext4_fs_i.h
index f1cd4934e46f..4377d249d378 100644
--- a/include/linux/ext4_fs_i.h
+++ b/include/linux/ext4_fs_i.h
@@ -139,16 +139,16 @@ struct ext4_inode_info {
         __u16 i_extra_isize;
 
         /*
-         * truncate_mutex is for serialising ext4_truncate() against
+         * i_data_sem is for serialising ext4_truncate() against
          * ext4_getblock().  In the 2.4 ext2 design, great chunks of inode's
          * data tree are chopped off during truncate. We can't do that in
          * ext4 because whenever we perform intermediate commits during
          * truncate, the inode and all the metadata blocks *must* be in a
          * consistent state which allows truncation of the orphans to restart
          * during recovery.  Hence we must fix the get_block-vs-truncate race
-         * by other means, so we have truncate_mutex.
+         * by other means, so we have i_data_sem.
          */
-        struct mutex truncate_mutex;
+        struct rw_semaphore i_data_sem;
         struct inode vfs_inode;
 
         unsigned long i_ext_generation;