linux-kernel - Re: [PATCH v2 4/6] iomap: correct the dirty length in page mkwrite

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Message-ID: <20240812164536.GE6043@frogsfrogsfrogs>
Date: Mon, 12 Aug 2024 09:45:36 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org, brauner@...nel.org,
	david@...morbit.com, jack@...e.cz, willy@...radead.org,
	yi.zhang@...wei.com, chengzhihao1@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v2 4/6] iomap: correct the dirty length in page mkwrite

On Mon, Aug 12, 2024 at 08:11:57PM +0800, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> When doing page mkwrite, iomap_folio_mkwrite_iter() dirty the entire
> folio by folio_mark_dirty() even the map length is shorter than one
> folio. However, on the filesystem with more than one blocks per folio,
> we'd better to only set counterpart block's dirty bit according to
> iomap_length(), so open code folio_mark_dirty() and pass the correct
> length.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> ---
>  fs/iomap/buffered-io.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 79031b7517e5..ac762de9a27f 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1492,7 +1492,10 @@ static loff_t iomap_folio_mkwrite_iter(struct iomap_iter *iter,
>  		block_commit_write(&folio->page, 0, length);
>  	} else {
>  		WARN_ON_ONCE(!folio_test_uptodate(folio));
> -		folio_mark_dirty(folio);
> +
> +		ifs_alloc(iter->inode, folio, 0);
> +		iomap_set_range_dirty(folio, 0, length);
> +		filemap_dirty_folio(iter->inode->i_mapping, folio);

Is it correct to be doing a lot more work by changing folio_mark_dirty
to filemap_dirty_folio?  Now pagefaults call __mark_inode_dirty which
they did not before.  Also, the folio itself must be marked dirty if any
of the ifs bitmap is marked dirty, so I don't understand the change
here.

--D

>  	}
>  
>  	return length;
> -- 
> 2.39.2
> 
>