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Message-ID: <CAFZ0FUXyxKT0cAUzkaMkE+PmoaErikcQDfL4Z_624BeqBR2WGw@mail.gmail.com>
Date: Fri, 15 Jun 2012 18:16:29 +0800
From: Robin Dong <hao.bigrat@...il.com>
To: Zheng Liu <gnehzuil.liu@...il.com>
Cc: linux-ext4@...r.kernel.org, Tao Ma <tm@....ma>,
Eric Sandeen <sandeen@...hat.com>,
Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [RFC][PATCH v2 3/3] ext4: add dio overwrite nolock
2012/6/14 Zheng Liu <gnehzuil.liu@...il.com>:
> From: Zheng Liu <wenqing.lz@...bao.com>
>
> Aligned and overwrite direct I/O can be parallelized. In ext4_file_dio_write,
> we first check whether these conditions are satisfied or not. If so, we
> take i_data_sem and release i_mutex lock directly. Meanwhile iocb->private is
> set to indicate that this is a dio overwrite, and it will be handled in
> ext4_ext_direct_IO.
>
> CC: Tao Ma <tm@....ma>
> CC: Eric Sandeen <sandeen@...hat.com>
> Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
> ---
> fs/ext4/file.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++--
> fs/ext4/inode.c | 27 +++++++++++++++++++++++++++
> 2 files changed, 78 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index a10dc77..812358f 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -93,9 +93,13 @@ static ssize_t
> ext4_file_dio_write(struct kiocb *iocb, const struct iovec *iov,
> unsigned long nr_segs, loff_t pos)
> {
> - struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
> + struct file *file = iocb->ki_filp;
> + struct inode *inode = file->f_mapping->host;
> + struct blk_plug plug;
> int unaligned_aio = 0;
> ssize_t ret;
> + int overwrite = 0;
> + size_t length = iov_length(iov, nr_segs);
>
> if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
> !is_sync_kiocb(iocb))
> @@ -115,7 +119,52 @@ ext4_file_dio_write(struct kiocb *iocb, const struct iovec *iov,
> ext4_aiodio_wait(inode);
> }
>
> - ret = generic_file_aio_write(iocb, iov, nr_segs, pos);
> + BUG_ON(iocb->ki_pos != pos);
> +
> + mutex_lock(&inode->i_mutex);
> + blk_start_plug(&plug);
> +
> + iocb->private = &overwrite;
> +
> + /* check whether we do a DIO overwrite or not */
> + if (ext4_should_dioread_nolock(inode) && !unaligned_aio &&
> + !file->f_mapping->nrpages && pos + length <= i_size_read(inode)) {
> + struct ext4_map_blocks map;
> + unsigned int blkbits = inode->i_blkbits;
> + int err, len;
> +
> + map.m_lblk = pos >> blkbits;
> + map.m_len = (EXT4_BLOCK_ALIGN(pos + length, blkbits) >> blkbits)
> + - map.m_lblk;
> + map.m_flags &= ~EXT4_MAP_FLAGS;
> + len = map.m_len;
> +
> + err = ext4_map_blocks(NULL, inode, &map, 0);
Nitpick:
May be better to change variable "err" to "ret"
> + /*
> + * 'err==len' means that all of blocks has been preallocated no
> + * matter they are initialized or not. For excluding
> + * uninitialized extents, we need to check m_flags. There are
> + * two conditions that indicate for initialized extents.
> + * 1) If we hit extent cache, EXT4_MAP_MAPPED flag is returned;
> + * 2) If we do a real lookup, non-flags are returned.
> + * So we should check these two conditions.
> + */
> + if (err == len && (!map.m_flags ||
> + map.m_flags & EXT4_MAP_MAPPED))
If we do a real lookup in ext4_map_blocks, it also return with
EXT4_MAP_MAPPED flag, the condition should be:
if (err == len && (map.m_flags & EXT4_MAP_MAPPED))
> + overwrite = 1;
> + }
> +
> + ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
> + mutex_unlock(&inode->i_mutex);
> +
> + if (ret > 0 || ret == -EIOCBQUEUED) {
> + ssize_t err;
> +
> + err = generic_write_sync(file, pos, ret);
> + if (err < 0 && ret > 0)
> + ret = err;
> + }
> + blk_finish_plug(&plug);
>
> if (unaligned_aio)
> mutex_unlock(ext4_aio_mutex(inode));
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 9a714ff..98e9096 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2996,6 +2996,26 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> if (rw == WRITE && final_size <= inode->i_size) {
> int overwrite = 0;
>
> + BUG_ON(iocb->private == NULL);
> +
> + /* If we do a overwrite dio, i_mutex locking can be released */
> + overwrite = *((int *)iocb->private);
> +
> + if (overwrite) {
> + down_read(&EXT4_I(inode)->i_data_sem);
> + mutex_unlock(&inode->i_mutex);
> + }
> +
> + /*
> + * If there are still some buffered I/O, we should fall back
> + * to take i_mutex locking.
> + */
> + if (overwrite && file->f_mapping->nrpages) {
> + overwrite = 0;
> + up_read(&EXT4_I(inode)->i_data_sem);
> + mutex_lock(&inode->i_mutex);
> + }
> +
> /*
> * We could direct write to holes and fallocate.
> *
> @@ -3083,6 +3103,13 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> ret = err;
> ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
> }
> +
> + /* take i_mutex locking again if we do a ovewrite dio */
> + if (overwrite) {
> + up_read(&EXT4_I(inode)->i_data_sem);
> + mutex_lock(&inode->i_mutex);
> + }
> +
> return ret;
> }
>
> --
> 1.7.4.1
>
> --
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--
--
Best Regard
Robin Dong
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