Re: [Ocfs2-devel] [PATCH v3 3/3] ocfs2: nowait aio support

[alex chen]

Hi Gang,

On 2017/12/28 18:07, Gang He wrote:
> Return -EAGAIN if any of the following checks fail for
> direct I/O with nowait flag:
> Can not get the related locks immediately,
> Blocks are not allocated at the write location, it will trigger
> block allocation, this will block IO operations.
> 
> Signed-off-by: Gang He <ghe@xxxxxxxx>
> ---
>  fs/ocfs2/dir.c         |  2 +-
>  fs/ocfs2/dlmglue.c     | 20 ++++++++---
>  fs/ocfs2/dlmglue.h     |  2 +-
>  fs/ocfs2/file.c        | 95 +++++++++++++++++++++++++++++++++++++++-----------
>  fs/ocfs2/mmap.c        |  2 +-
>  fs/ocfs2/ocfs2_trace.h | 10 +++---
>  6 files changed, 99 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
> index febe631..ea50901 100644
> --- a/fs/ocfs2/dir.c
> +++ b/fs/ocfs2/dir.c
> @@ -1957,7 +1957,7 @@ int ocfs2_readdir(struct file *file, struct dir_context *ctx)
>  
>  	trace_ocfs2_readdir((unsigned long long)OCFS2_I(inode)->ip_blkno);
>  
> -	error = ocfs2_inode_lock_atime(inode, file->f_path.mnt, &lock_level);
> +	error = ocfs2_inode_lock_atime(inode, file->f_path.mnt, &lock_level, 1);
>  	if (lock_level && error >= 0) {
>  		/* We release EX lock which used to update atime
>  		 * and get PR lock again to reduce contention
> diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
> index a68efa3..07e169f 100644
> --- a/fs/ocfs2/dlmglue.c
> +++ b/fs/ocfs2/dlmglue.c
> @@ -2515,13 +2515,18 @@ int ocfs2_inode_lock_with_page(struct inode *inode,
>  
>  int ocfs2_inode_lock_atime(struct inode *inode,
>  			  struct vfsmount *vfsmnt,
> -			  int *level)
> +			  int *level, int wait)
>  {
>  	int ret;
>  
> -	ret = ocfs2_inode_lock(inode, NULL, 0);
> +	if (wait)
> +		ret = ocfs2_inode_lock(inode, NULL, 0);
> +	else
> +		ret = ocfs2_try_inode_lock(inode, NULL, 0);
> +
>  	if (ret < 0) {
> -		mlog_errno(ret);
> +		if (ret != -EAGAIN)
> +			mlog_errno(ret);
>  		return ret;
>  	}
>  
> @@ -2533,9 +2538,14 @@ int ocfs2_inode_lock_atime(struct inode *inode,
>  		struct buffer_head *bh = NULL;
>  
>  		ocfs2_inode_unlock(inode, 0);
> -		ret = ocfs2_inode_lock(inode, &bh, 1);
> +		if (wait)
> +			ret = ocfs2_inode_lock(inode, &bh, 1);
> +		else
> +			ret = ocfs2_try_inode_lock(inode, &bh, 1);
> +
>  		if (ret < 0) {
> -			mlog_errno(ret);
> +			if (ret != -EAGAIN)
> +				mlog_errno(ret);
>  			return ret;
>  		}
>  		*level = 1;
> diff --git a/fs/ocfs2/dlmglue.h b/fs/ocfs2/dlmglue.h
> index 05910fc..c83dbb5 100644
> --- a/fs/ocfs2/dlmglue.h
> +++ b/fs/ocfs2/dlmglue.h
> @@ -123,7 +123,7 @@ void ocfs2_refcount_lock_res_init(struct ocfs2_lock_res *lockres,
>  void ocfs2_open_unlock(struct inode *inode);
>  int ocfs2_inode_lock_atime(struct inode *inode,
>  			  struct vfsmount *vfsmnt,
> -			  int *level);
> +			  int *level, int wait);
>  int ocfs2_inode_lock_full_nested(struct inode *inode,
>  			 struct buffer_head **ret_bh,
>  			 int ex,
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index a1d0510..caef9b1 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -140,6 +140,8 @@ static int ocfs2_file_open(struct inode *inode, struct file *file)
>  		spin_unlock(&oi->ip_lock);
>  	}
>  
> +	file->f_mode |= FMODE_NOWAIT;
> +
>  leave:
>  	return status;
>  }
> @@ -2132,12 +2134,12 @@ static int ocfs2_prepare_inode_for_refcount(struct inode *inode,
>  }
>  
>  static int ocfs2_prepare_inode_for_write(struct file *file,
> -					 loff_t pos,
> -					 size_t count)
> +					 loff_t pos, size_t count, int wait)
>  {
> -	int ret = 0, meta_level = 0;
> +	int ret = 0, meta_level = 0, overwrite_io = 0;
>  	struct dentry *dentry = file->f_path.dentry;
>  	struct inode *inode = d_inode(dentry);
> +	struct buffer_head *di_bh = NULL;
>  	loff_t end;
>  
>  	/*
> @@ -2145,13 +2147,40 @@ static int ocfs2_prepare_inode_for_write(struct file *file,
>  	 * if we need to make modifications here.
>  	 */
>  	for(;;) {
> -		ret = ocfs2_inode_lock(inode, NULL, meta_level);
> +		if (wait)
> +			ret = ocfs2_inode_lock(inode, NULL, meta_level);
> +		else
> +			ret = ocfs2_try_inode_lock(inode,
> +				overwrite_io ? NULL : &di_bh, meta_level);
>  		if (ret < 0) {
>  			meta_level = -1;
> -			mlog_errno(ret);
> +			if (ret != -EAGAIN)
> +				mlog_errno(ret);
>  			goto out;
>  		}
>  
> +		/*
> +		 * Check if IO will overwrite allocated blocks in case
> +		 * IOCB_NOWAIT flag is set.
> +		 */
> +		if (!wait && !overwrite_io) {
> +			overwrite_io = 1;
> +			if (!down_read_trylock(&OCFS2_I(inode)->ip_alloc_sem)) {
> +				ret = -EAGAIN;
> +				goto out_unlock;
> +			}
> +
> +			ret = ocfs2_overwrite_io(inode, di_bh, pos, count);
> +			brelse(di_bh);
> +			di_bh = NULL;
> +			up_read(&OCFS2_I(inode)->ip_alloc_sem);
> +			if (ret < 0) {
> +				if (ret != -EAGAIN)
> +					mlog_errno(ret);
> +				goto out_unlock;
> +			}
> +		}
> +
>  		/* Clear suid / sgid if necessary. We do this here
>  		 * instead of later in the write path because
>  		 * remove_suid() calls ->setattr without any hint that
> @@ -2199,7 +2228,9 @@ static int ocfs2_prepare_inode_for_write(struct file *file,
>  
>  out_unlock:
>  	trace_ocfs2_prepare_inode_for_write(OCFS2_I(inode)->ip_blkno,
> -					    pos, count);
> +					    pos, count, wait);
> +
> +	brelse(di_bh);
>  
>  	if (meta_level >= 0)
>  		ocfs2_inode_unlock(inode, meta_level);
> @@ -2211,7 +2242,7 @@ static int ocfs2_prepare_inode_for_write(struct file *file,
>  static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
>  				    struct iov_iter *from)
>  {
> -	int direct_io, rw_level;
> +	int rw_level;
>  	ssize_t written = 0;
>  	ssize_t ret;
>  	size_t count = iov_iter_count(from);
> @@ -2223,6 +2254,8 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
>  	void *saved_ki_complete = NULL;
>  	int append_write = ((iocb->ki_pos + count) >=
>  			i_size_read(inode) ? 1 : 0);
> +	int direct_io = iocb->ki_flags & IOCB_DIRECT ? 1 : 0;
> +	int nowait = iocb->ki_flags & IOCB_NOWAIT ? 1 : 0;
>  
>  	trace_ocfs2_file_aio_write(inode, file, file->f_path.dentry,
>  		(unsigned long long)OCFS2_I(inode)->ip_blkno,
> @@ -2230,12 +2263,17 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
>  		file->f_path.dentry->d_name.name,
>  		(unsigned int)from->nr_segs);	/* GRRRRR */
>  
> +	if (!direct_io && nowait)
> +		return -EOPNOTSUPP;
> +
>  	if (count == 0)
>  		return 0;
>  
> -	direct_io = iocb->ki_flags & IOCB_DIRECT ? 1 : 0;
> -
> -	inode_lock(inode);
I think we only need check the nowait here because we already check if the 'IOCB_DIRECT'
flag and the 'IOCB_NOWAIT' flag are both set in the front of this function.

> +	if (direct_io && nowait) {
> +		if (!inode_trylock(inode))
> +			return -EAGAIN;
> +	} else
> +		inode_lock(inode);
>  
>  	/*
>  	 * Concurrent O_DIRECT writes are allowed with
> @@ -2244,9 +2282,13 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
>  	 */
>  	rw_level = (!direct_io || full_coherency || append_write);
>  
> -	ret = ocfs2_rw_lock(inode, rw_level);
> +	if (direct_io && nowait)
> +		ret = ocfs2_try_rw_lock(inode, rw_level);
> +	else
> +		ret = ocfs2_rw_lock(inode, rw_level);
>  	if (ret < 0) {
> -		mlog_errno(ret);
> +		if (ret != -EAGAIN)
> +			mlog_errno(ret);
>  		goto out_mutex;
>  	}
>  
> @@ -2260,9 +2302,13 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
>  		 * other nodes to drop their caches.  Buffered I/O
>  		 * already does this in write_begin().
>  		 */
> -		ret = ocfs2_inode_lock(inode, NULL, 1);
> +		if (nowait)
> +			ret = ocfs2_try_inode_lock(inode, NULL, 1);
> +		else
> +			ret = ocfs2_inode_lock(inode, NULL, 1);
>  		if (ret < 0) {
> -			mlog_errno(ret);
> +			if (ret != -EAGAIN)
> +				mlog_errno(ret);
>  			goto out;
>  		}
>  
> @@ -2277,9 +2323,10 @@ static ssize_t ocfs2_file_write_iter(struct kiocb *iocb,
>  	}
>  	count = ret;
>  
> -	ret = ocfs2_prepare_inode_for_write(file, iocb->ki_pos, count);
> +	ret = ocfs2_prepare_inode_for_write(file, iocb->ki_pos, count, !nowait);
>  	if (ret < 0) {
> -		mlog_errno(ret);
> +		if (ret != -EAGAIN)
> +			mlog_errno(ret);
>  		goto out;
>  	}
>  
> @@ -2355,6 +2402,7 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
>  	int ret = 0, rw_level = -1, lock_level = 0;
>  	struct file *filp = iocb->ki_filp;
>  	struct inode *inode = file_inode(filp);
> +	int nowait = iocb->ki_flags & IOCB_NOWAIT ? 1 : 0;
>  
Here should we check if the 'IOCB_DIRECT' flag and the 'IOCB_NOWAIT' flag are both set?

Thanks,
Alex

>  	trace_ocfs2_file_aio_read(inode, filp, filp->f_path.dentry,
>  			(unsigned long long)OCFS2_I(inode)->ip_blkno,
> @@ -2374,9 +2422,14 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
>  	 * need locks to protect pending reads from racing with truncate.
>  	 */
>  	if (iocb->ki_flags & IOCB_DIRECT) {
> -		ret = ocfs2_rw_lock(inode, 0);
> +		if (nowait)
> +			ret = ocfs2_try_rw_lock(inode, 0);
> +		else
> +			ret = ocfs2_rw_lock(inode, 0);
> +
>  		if (ret < 0) {
> -			mlog_errno(ret);
> +			if (ret != -EAGAIN)
> +				mlog_errno(ret);
>  			goto bail;
>  		}
>  		rw_level = 0;
> @@ -2393,9 +2446,11 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
>  	 * like i_size. This allows the checks down below
>  	 * generic_file_aio_read() a chance of actually working.
>  	 */
> -	ret = ocfs2_inode_lock_atime(inode, filp->f_path.mnt, &lock_level);
> +	ret = ocfs2_inode_lock_atime(inode, filp->f_path.mnt, &lock_level,
> +				     !nowait);
>  	if (ret < 0) {
> -		mlog_errno(ret);
> +		if (ret != -EAGAIN)
> +			mlog_errno(ret);
>  		goto bail;
>  	}
>  	ocfs2_inode_unlock(inode, lock_level);
> diff --git a/fs/ocfs2/mmap.c b/fs/ocfs2/mmap.c
> index 098f5c7..fb9a20e 100644
> --- a/fs/ocfs2/mmap.c
> +++ b/fs/ocfs2/mmap.c
> @@ -184,7 +184,7 @@ int ocfs2_mmap(struct file *file, struct vm_area_struct *vma)
>  	int ret = 0, lock_level = 0;
>  
>  	ret = ocfs2_inode_lock_atime(file_inode(file),
> -				    file->f_path.mnt, &lock_level);
> +				    file->f_path.mnt, &lock_level, 1);
>  	if (ret < 0) {
>  		mlog_errno(ret);
>  		goto out;
> diff --git a/fs/ocfs2/ocfs2_trace.h b/fs/ocfs2/ocfs2_trace.h
> index a0b5d00..e2a11aa 100644
> --- a/fs/ocfs2/ocfs2_trace.h
> +++ b/fs/ocfs2/ocfs2_trace.h
> @@ -1449,20 +1449,22 @@
>  
>  TRACE_EVENT(ocfs2_prepare_inode_for_write,
>  	TP_PROTO(unsigned long long ino, unsigned long long saved_pos,
> -		 unsigned long count),
> -	TP_ARGS(ino, saved_pos, count),
> +		 unsigned long count, int wait),
> +	TP_ARGS(ino, saved_pos, count, wait),
>  	TP_STRUCT__entry(
>  		__field(unsigned long long, ino)
>  		__field(unsigned long long, saved_pos)
>  		__field(unsigned long, count)
> +		__field(int, wait)
>  	),
>  	TP_fast_assign(
>  		__entry->ino = ino;
>  		__entry->saved_pos = saved_pos;
>  		__entry->count = count;
> +		__entry->wait = wait;
>  	),
> -	TP_printk("%llu %llu %lu", __entry->ino,
> -		  __entry->saved_pos, __entry->count)
> +	TP_printk("%llu %llu %lu %d", __entry->ino,
> +		  __entry->saved_pos, __entry->count, __entry->wait)
>  );
>  
>  DEFINE_OCFS2_INT_EVENT(generic_file_aio_read_ret);
>