>From 7de4ca30e0c897bbdd49eae0fdec5132744c105a Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Thu, 22 Sep 2016 14:20:15 +0200 Subject: [PATCH] ext4: Allow parallel DIO reads We can easily support parallel direct IO reads. We only have to make sure we cannot expose uninitialized data by reading allocated block to which data was not written yet, or which was already truncated. That is easily achieved by holding inode_lock in shared mode - that excludes all writes, truncates, hole punches. We also have to guard against page writeback allocating blocks for delay-allocated pages - that race is handled by the fact that we writeback all the pages in the affected range and the lock protects us from new pages being created there. Signed-off-by: Jan Kara --- fs/ext4/inode.c | 40 ++++++++++++++++++---------------------- 1 file changed, 18 insertions(+), 22 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index c6ea25a190f8..0af52f012bfb 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -3526,35 +3526,31 @@ out: static ssize_t ext4_direct_IO_read(struct kiocb *iocb, struct iov_iter *iter) { - int unlocked = 0; - struct inode *inode = iocb->ki_filp->f_mapping->host; + struct address_space *mapping = iocb->ki_filp->f_mapping; + struct inode *inode = mapping->host; ssize_t ret; - if (ext4_should_dioread_nolock(inode)) { - /* - * Nolock dioread optimization may be dynamically disabled - * via ext4_inode_block_unlocked_dio(). Check inode's state - * while holding extra i_dio_count ref. - */ - inode_dio_begin(inode); - smp_mb(); - if (unlikely(ext4_test_inode_state(inode, - EXT4_STATE_DIOREAD_LOCK))) - inode_dio_end(inode); - else - unlocked = 1; - } + /* + * Shared inode_lock is enough for us - it protects against concurrent + * writes & truncates and since we take care of writing back page cache, + * we are protected against page writeback as well. + */ + inode_lock_shared(inode); if (IS_DAX(inode)) { - ret = dax_do_io(iocb, inode, iter, ext4_dio_get_block, - NULL, unlocked ? 0 : DIO_LOCKING); + ret = dax_do_io(iocb, inode, iter, ext4_dio_get_block, NULL, 0); } else { + size_t count = iov_iter_count(iter); + + ret = filemap_write_and_wait_range(mapping, iocb->ki_pos, + iocb->ki_pos + count); + if (ret) + goto out_unlock; ret = __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev, iter, ext4_dio_get_block, - NULL, NULL, - unlocked ? 0 : DIO_LOCKING); + NULL, NULL, 0); } - if (unlocked) - inode_dio_end(inode); +out_unlock: + inode_unlock_shared(inode); return ret; } -- 2.6.6