Re: [PATCH v2 6/6] iomap: reduce unnecessary state_lock when setting ifs uptodate and dirty bits

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Mon, Aug 12, 2024 at 08:11:59PM +0800, Zhang Yi wrote:
> @@ -866,9 +899,8 @@ static bool __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
>  	 */
>  	if (unlikely(copied < len && !folio_test_uptodate(folio)))
>  		return false;
> -	iomap_set_range_uptodate(folio, offset_in_folio(folio, pos), len);
> -	iomap_set_range_dirty(folio, offset_in_folio(folio, pos), copied);
> -	filemap_dirty_folio(inode->i_mapping, folio);
> +
> +	iomap_set_range_dirty_uptodate(folio, from, copied);
>  	return true;

I wonder how often we overwrite a completely uptodate folio rather than
writing new data to a fresh folio?  iow, would this be a measurable
optimisation?

	if (folio_test_uptodate(folio))
		iomap_set_range_dirty(folio, from, copied);
	else
		iomap_set_range_dirty_uptodate(folio, from, copied);