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

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Message-ID: <Zro_yj3agfdhM16Q@casper.infradead.org>
Date: Mon, 12 Aug 2024 18:00:58 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, djwong@...nel.org, hch@...radead.org,
	brauner@...nel.org, david@...morbit.com, jack@...e.cz,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 6/6] iomap: reduce unnecessary state_lock when setting
 ifs uptodate and dirty bits

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);