linux-kernel - Re: [PATCH v2 4/4] iomap: don't abandon the whole thing with iomap_folio

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Message-ID: <20250811121803.1026731-1-alexjlzheng@tencent.com>
Date: Mon, 11 Aug 2025 20:18:03 +0800
From: Jinliang Zheng <alexjlzheng@...il.com>
To: hch@...radead.org
Cc: alexjlzheng@...il.com,
	alexjlzheng@...cent.com,
	brauner@...nel.org,
	djwong@...nel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-xfs@...r.kernel.org
Subject: Re: [PATCH v2 4/4] iomap: don't abandon the whole thing with iomap_folio_state

On Mon, 11 Aug 2025 03:41:39 -0700, Christoph Hellwig wrote:
> Where "the whole thing" is the current iteration in the write loop.
> Can you spell this out a bit better?

Hahaha, I was also confused about "the whole thing". I guess it refers to a
partial write in a folio. It appears in the comments of __iomap_write_end().

static bool __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
		size_t copied, struct folio *folio)
{
	flush_dcache_folio(folio);

	/*
	 * The blocks that were entirely written will now be uptodate, so we
	 * don't have to worry about a read_folio reading them and overwriting a
	 * partial write.  However, if we've encountered a short write and only
	 * partially written into a block, it will not be marked uptodate, so a
	 * read_folio might come in and destroy our partial write.
	 *
	 * Do the simplest thing and just treat any short write to a
	 * non-uptodate page as a zero-length write, and force the caller to
	 * redo the whole thing.
                ^^^^^^^^^^^^^^^ <------------------ look look look, it's here :)
	 */
	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);
	return true;
}

> 
> Also please include the rationale why you are changing the logic
> here in the commit log.

Hahaha, what I want to express is that we no longer need to define partial write
based on folio granularity, it is more appropriate to use block granularity.

Please forgive my poor English. :-<

thanks,
Jinliang Zheng :)