Re: [PATCH] iomap: Do not create fake iter in iomap_dio_bio_actor()

[Matthew Bobrowski <mbobrowski@mbobrowski.org>]

On Mon, Nov 25, 2019 at 12:18:57PM +0100, Jan Kara wrote:
> iomap_dio_bio_actor() copies iter to a local variable and then limits it
> to a file extent we have mapped. When IO is submitted,
> iomap_dio_bio_actor() advances the original iter while the copied iter
> is advanced inside bio_iov_iter_get_pages(). This logic is non-obvious
> especially because both iters still point to same shared structures
> (such as pipe info) so if iov_iter_advance() changes anything in the
> shared structure, this scheme breaks. Let's just truncate and reexpand
> the original iter as needed instead of playing games with copying iters
> and keeping them in sync.

Looks good. Just one minor nit below which is eating me. I guess
Darrick can fix it up when applying it to his tree, if deemed
necessary to fix up.

Feel free to add:

Reviewed-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>

>  	/*
> -	 * Operate on a partial iter trimmed to the extent we were called for.
> -	 * We'll update the iter in the dio once we're done with this extent.
> +	 * Save the original count and trim the iter to just the extent we
> +	 * are operating on right now.  The iter will be re-expanded once
  	       		    	      ^^
				      Extra whitespace here.

IMO, I think we can word the last sentence a little better too i.e.

/*                                                                               
 * Save the original count and trim the iter to the extent that we're            
 * currently operating on right now. The iter will then again be                 
 * expanded out once we're done.                                                 
 */

/M