linux-ext4 - Re: [PATCH 4/6] fs-verity: support reading Merkle tree with ioctl

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Message-ID: <YBIeoGowXVrG3QfU@sol.localdomain>
Date:   Wed, 27 Jan 2021 18:17:04 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-api@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Victor Hsieh <victorhsieh@...gle.com>
Subject: Re: [PATCH 4/6] fs-verity: support reading Merkle tree with ioctl

On Wed, Jan 27, 2021 at 05:10:39PM -0800, Jaegeuk Kim wrote:
> 
> Minor thought:
> How about invalidating or truncating merkel tree pages?
> 
> Reviewed-by: Jaegeuk Kim <jaegeuk@...nel.org>
> 

Removing them from the page cache after the read, you mean?  I'm not sure we can
assume that users of this ioctl would want the pages to *not* be cached, any
more than we could assume that for any regular read().  I think we should just
leave the pages cached (like a regular read) and not do anything special.  Like
other pagecache pages, the kernel will evict the Merkle tree pages eventually if
they aren't being accessed anymore and memory needs to be reclaimed.

- Eric