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Date: Fri, 27 Feb 2026 14:29:50 -0800
From: Eric Biggers <ebiggers@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: "Theodore Y. Ts'o" <tytso@mit.edu>, Jaegeuk Kim <jaegeuk@kernel.org>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Chao Yu <chao@kernel.org>, Christian Brauner <brauner@kernel.org>,
	"Darrick J. Wong" <djwong@kernel.org>,
	linux-fscrypt@vger.kernel.org, linux-ext4@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 14/14] ext4: use a byte granularity cursor in
 ext4_mpage_readpages
Message-ID: <20260227222950.GC5357@quark>
References: <20260226144954.142278-1-hch@lst.de>
 <20260226144954.142278-15-hch@lst.de>
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In-Reply-To: <20260226144954.142278-15-hch@lst.de>

On Thu, Feb 26, 2026 at 06:49:34AM -0800, Christoph Hellwig wrote:
> +		block_in_file = EXT4_PG_TO_LBLK(inode, folio->index);
> +		pos = (loff_t)block_in_file << blkbits;

The EXT4_PG_TO_LBLK() expands to:

        (((loff_t)(folio->index) << PAGE_SHIFT) >> (inode)->i_blkbits)

So it calculates the pos as an intermediate step, and we end up with the
redundant pos = (pos >> blkbits) << blkbits.

It probably would make more sense to calculate the pos first, similar to
what other places in this series do:

        pos = folio_pos(folio);                                          
        block_in_file = pos >> blkbits;

- Eric