Re: [PATCH] Add block device speciffic splice write method

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 20 Oct 2008 20:11:56 +0200 Jens Axboe <jens.axboe@oracle.com> wrote:

> +ssize_t generic_file_splice_write_file_nolock(struct pipe_inode_info *pipe,
> +					      struct file *out, loff_t *ppos,
> +					      size_t len, unsigned int flags)
> +{
> +	struct address_space *mapping = out->f_mapping;
> +	struct inode *inode = mapping->host;
> +	struct splice_desc sd = {
> +		.total_len = len,
> +		.flags = flags,
> +		.pos = *ppos,
> +		.u.file = out,
> +	};
> +	ssize_t ret;
> +
> +	mutex_lock(&pipe->inode->i_mutex);
> +	ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
> +	mutex_unlock(&pipe->inode->i_mutex);
> +
> +	if (ret > 0) {
> +		unsigned long nr_pages;
> +
> +		*ppos += ret;
> +		nr_pages = (ret + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
> +
> +		if (unlikely((out->f_flags & O_SYNC) || IS_SYNC(inode))) {
> +			int er;
> +
> +			er = sync_page_range_nolock(inode, mapping, *ppos, ret);
> +			if (er)
> +				ret = er;
> +		}
> +		balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(generic_file_splice_write_file_nolock);

I don't think the balance_dirty_pages() is needed if we just did the
sync_page_range().


But really it'd be better if the throttling happened down in
pipe_to_file(), on a per-page basis.  As it stands we can dirty an
arbitrary number of pagecache pages without throttling.  I think?