linux-ext4 - Re: [PATCH v2] fs-verity: implement readahead of Merkle tree pages

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Message-ID: <20200114001407.GO76141@mit.edu>
Date:   Mon, 13 Jan 2020 19:14:07 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, Victor Hsieh <victorhsieh@...gle.com>,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH v2] fs-verity: implement readahead of Merkle tree pages

On Mon, Jan 06, 2020 at 12:55:33PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
> 
> When fs-verity verifies data pages, currently it reads each Merkle tree
> page synchronously using read_mapping_page().
> 
> Therefore, when the Merkle tree pages aren't already cached, fs-verity
> causes an extra 4 KiB I/O request for every 512 KiB of data (assuming
> that the Merkle tree uses SHA-256 and 4 KiB blocks).  This results in
> more I/O requests and performance loss than is strictly necessary.
> 
> Therefore, implement readahead of the Merkle tree pages.

Looks good.   Feel free to add:

Reviewed-by: Theodore Ts'o <tytso@....edu>

(for the ext4 and fs/verity bits)