Re: [PATCH v2 1/3] iomap: don't mark the inode dirty in iomap_write_end

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Jun 26, 2019 at 03:23:33PM +0200, Andreas Gruenbacher wrote:
> Marking the inode dirty for each page copied into the page cache can be
> very inefficient for file systems that use the VFS dirty inode tracking,
> and is completely pointless for those that don't use the VFS dirty inode
> tracking.  So instead, only set an iomap flag when changing the in-core
> inode size, and open code the rest of __generic_write_end.
> 
> Partially based on code from Christoph Hellwig.
> 
> Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/gfs2/bmap.c        |  2 ++
>  fs/iomap.c            | 15 ++++++++++++++-
>  include/linux/iomap.h |  1 +
>  3 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
> index 93ea1d529aa3..f4b895fc632d 100644
> --- a/fs/gfs2/bmap.c
> +++ b/fs/gfs2/bmap.c
> @@ -1182,6 +1182,8 @@ static int gfs2_iomap_end(struct inode *inode, loff_t pos, loff_t length,
>  
>  	if (ip->i_qadata && ip->i_qadata->qa_qd_num)
>  		gfs2_quota_unlock(ip);
> +	if (iomap->flags & IOMAP_F_SIZE_CHANGED)
> +		mark_inode_dirty(inode);
>  	gfs2_write_unlock(inode);
>  
>  out:
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 12654c2e78f8..97569064faaa 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -777,6 +777,7 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
>  		unsigned copied, struct page *page, struct iomap *iomap)
>  {
>  	const struct iomap_page_ops *page_ops = iomap->page_ops;
> +	loff_t old_size = inode->i_size;
>  	int ret;
>  
>  	if (iomap->type == IOMAP_INLINE) {
> @@ -788,7 +789,19 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
>  		ret = __iomap_write_end(inode, pos, len, copied, page, iomap);
>  	}
>  
> -	__generic_write_end(inode, pos, ret, page);
> +	/*
> +	 * Update the in-memory inode size after copying the data into the page
> +	 * cache.  It's up to the file system to write the updated size to disk,
> +	 * preferably after I/O completion so that no stale data is exposed.
> +	 */
> +	if (pos + ret > old_size) {
> +		i_size_write(inode, pos + ret);
> +		iomap->flags |= IOMAP_F_SIZE_CHANGED;
> +	}
> +	unlock_page(page);
> +
> +	if (old_size < pos)
> +		pagecache_isize_extended(inode, old_size, pos);
>  	if (page_ops && page_ops->page_done)
>  		page_ops->page_done(inode, pos, copied, page, iomap);
>  	put_page(page);
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 2103b94cb1bf..1df9ea187a9a 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -35,6 +35,7 @@ struct vm_fault;
>  #define IOMAP_F_NEW		0x01	/* blocks have been newly allocated */
>  #define IOMAP_F_DIRTY		0x02	/* uncommitted metadata */
>  #define IOMAP_F_BUFFER_HEAD	0x04	/* file system requires buffer heads */
> +#define IOMAP_F_SIZE_CHANGED	0x08	/* file size has changed */
>  
>  /*
>   * Flags that only need to be reported for IOMAP_REPORT requests:
> -- 
> 2.20.1
>