From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-fscrypt@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-ext4@vger.kernel.org, Victor Hsieh <victorhsieh@google.com>,
linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [PATCH v3] fs-verity: implement readahead for FS_IOC_ENABLE_VERITY
Date: Mon, 13 Jan 2020 19:41:37 -0500 [thread overview]
Message-ID: <20200114004137.GQ76141@mit.edu> (raw)
In-Reply-To: <20200106205410.136707-1-ebiggers@kernel.org>
On Mon, Jan 06, 2020 at 12:54:10PM -0800, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@google.com>
>
> When it builds the first level of the Merkle tree, FS_IOC_ENABLE_VERITY
> sequentially reads each page of the file using read_mapping_page().
> This works fine if the file's data is already in pagecache, which should
> normally be the case, since this ioctl is normally used immediately
> after writing out the file.
>
> But in any other case this implementation performs very poorly, since
> only one page is read at a time.
>
> Fix this by implementing readahead using the functions from
> mm/readahead.c.
>
> This improves performance in the uncached case by about 20x, as seen in
> the following benchmarks done on a 250MB file (on x86_64 with SHA-NI):
>
> FS_IOC_ENABLE_VERITY uncached (before) 3.299s
> FS_IOC_ENABLE_VERITY uncached (after) 0.160s
> FS_IOC_ENABLE_VERITY cached 0.147s
> sha256sum uncached 0.191s
> sha256sum cached 0.145s
>
> Note: we could instead switch to kernel_read(). But that would mean
> we'd no longer be hashing the data directly from the pagecache, which is
> a nice optimization of its own. And using kernel_read() would require
> allocating another temporary buffer, hashing the data and tree pages
> separately, and explicitly zero-padding the last page -- so it wouldn't
> really be any simpler than direct pagecache access, at least for now.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
Looks good, feel free to add:
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
next prev parent reply other threads:[~2020-01-14 0:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-06 20:54 [PATCH v3] fs-verity: implement readahead for FS_IOC_ENABLE_VERITY Eric Biggers
2020-01-14 0:41 ` Theodore Y. Ts'o [this message]
2020-01-14 21:32 ` Eric Biggers
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200114004137.GQ76141@mit.edu \
--to=tytso@mit.edu \
--cc=ebiggers@kernel.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-f2fs-devel@lists.sourceforge.net \
--cc=linux-fscrypt@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=victorhsieh@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).