From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Jeff Layton <jlayton@kernel.org>,
Kent Overstreet <kent.overstreet@linux.dev>,
Christian Brauner <brauner@kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
John Stultz <jstultz@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Stephen Boyd <sboyd@kernel.org>,
Chandan Babu R <chandan.babu@oracle.com>,
"Darrick J. Wong" <djwong@kernel.org>,
"Theodore Ts'o" <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>,
Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
David Sterba <dsterba@suse.com>, Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Amir Goldstein <amir73il@gmail.com>, Jan Kara <jack@suse.de>,
David Howells <dhowells@redhat.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-btrfs@vger.kernel.org, linux-mm@kvack.org,
linux-nfs@vger.kernel.org
Subject: Re: [PATCH RFC 2/9] timekeeping: new interfaces for multigrain timestamp handing
Date: Mon, 23 Oct 2023 18:10:15 -1000 [thread overview]
Message-ID: <CAHk-=wjUWM8VVJxUYb=XfqvrS38ACS8RxK2ac9qGp9FDT=USkw@mail.gmail.com> (raw)
In-Reply-To: <ZTc8tClCRkfX3kD7@dread.disaster.area>
On Mon, 23 Oct 2023 at 17:40, Dave Chinner <david@fromorbit.com> wrote:
> >
> > Maybe we don't even need a mode, and could just decide that atime
> > updates aren't i_version updates at all?
>
> We do that already - in memory atime updates don't bump i_version at
> all. The issue is the rare persistent atime update requests that
> still happen - they are the ones that trigger an i_version bump on
> XFS, and one of the relatime heuristics tickle this specific issue.
Yes, yes, but that's what I kind of allude to - maybe people still
want the on-disk atime updates, but do they actually want the
i_version updates just because they want more aggressive atime
updates?
> > Or maybe i_version can update, but callers of getattr() could have two
> > bits for that STATX_CHANGE_COOKIE, one for "I care about atime" and
> > one for others, and we'd pass that down to inode_query_version, and
> > we'd have a I_VERSION_QUERIED and a I_VERSION_QUERIED_STRICT, and the
> > "I care about atime" case ould set the strict one.
>
> This makes correct behaviour reliant on the applicaiton using the
> query mechanism correctly. I have my doubts that userspace
> developers will be able to understand the subtle difference between
> the two options and always choose correctly....
I don't think we _have_ a user space interface.
At least the STATX_CHANGE_COOKIE bit isn't exposed to user space at
all. Not in the uapi headers, but not even in xstat():
/* STATX_CHANGE_COOKIE is kernel-only for now */
tmp.stx_mask = stat->result_mask & ~STATX_CHANGE_COOKIE;
So the *only* users of STATX_CHANGE_COOKIE seem to be entirely
in-kernel, unless there is something I'm missing where somebody uses
i_version through some other interface (random ioctl?).
End result: splitting STATX_CHANGE_COOKIE into a "I don't care about
atime" and a "give me all change events" shouldn't possibly break
anything that I can see.
The only other uses of inode_query_iversion() seem to be the explicit
directory optimizations (ie the "I'm caching the offset and don't want
to re-check that it's valid unless required, so give me the inode
version for the directory as a way to decide if I need to re-check"
thing).
And those *definitely* don't want i_version updates on any atime updates.
There might be some other use of inode_query_iversion() that I missed,
of course. But from a quick look, it really looks to me like we can
relax our i_version updates.
Linus
next prev parent reply other threads:[~2023-10-24 4:11 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-18 17:41 [PATCH RFC 0/9] fs: multigrain timestamps (redux) Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 1/9] fs: switch timespec64 fields in inode to discrete integers Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 2/9] timekeeping: new interfaces for multigrain timestamp handing Jeff Layton
2023-10-18 19:18 ` Linus Torvalds
2023-10-18 20:47 ` Jeff Layton
2023-10-18 21:31 ` Linus Torvalds
2023-10-18 21:52 ` Jeff Layton
2023-10-19 9:29 ` Christian Brauner
2023-10-19 11:28 ` Jeff Layton
2023-10-19 22:02 ` Dave Chinner
2023-10-20 12:12 ` Jeff Layton
2023-10-20 20:06 ` Linus Torvalds
2023-10-20 20:20 ` Linus Torvalds
2023-10-20 21:05 ` Jeff Layton
2023-10-22 22:17 ` Dave Chinner
2023-10-23 14:45 ` Jeff Layton
2023-10-23 23:26 ` Dave Chinner
2023-10-24 0:18 ` Linus Torvalds
2023-10-24 3:40 ` Dave Chinner
2023-10-24 4:10 ` Linus Torvalds [this message]
2023-10-24 7:08 ` Amir Goldstein
2023-10-24 18:40 ` Jeff Layton
2023-10-25 8:05 ` Dave Chinner
2023-10-25 10:41 ` Amir Goldstein
2023-10-25 12:25 ` Jeff Layton
2023-10-26 2:20 ` Dave Chinner
2023-10-26 5:42 ` Amir Goldstein
2023-10-27 10:35 ` Jeff Layton
2023-10-30 22:37 ` Dave Chinner
2023-10-30 23:11 ` Linus Torvalds
2023-10-31 1:42 ` Dave Chinner
2023-10-31 7:03 ` Amir Goldstein
2023-10-31 10:30 ` Christian Brauner
2023-10-31 11:29 ` Jeff Layton
2023-10-31 21:57 ` Dave Chinner
2023-10-31 23:02 ` Darrick J. Wong
2023-10-31 23:47 ` Dave Chinner
2023-11-01 10:16 ` Jan Kara
2023-11-01 11:38 ` Amir Goldstein
2023-11-02 10:17 ` Jeff Layton
2023-11-01 20:10 ` Linus Torvalds
2023-11-01 21:34 ` Trond Myklebust
2023-11-01 22:23 ` Linus Torvalds
2023-11-01 22:45 ` Trond Myklebust
2023-11-01 23:29 ` Dave Chinner
2023-11-02 10:29 ` Jeff Layton
2023-11-02 10:15 ` Jeff Layton
2023-10-31 23:12 ` Darrick J. Wong
2023-11-01 8:08 ` Amir Goldstein
2023-10-31 11:26 ` Jeff Layton
2023-10-31 19:43 ` John Stoffel
2023-10-31 11:04 ` Jeff Layton
2023-10-31 12:22 ` Jan Kara
2023-10-31 12:55 ` Jeff Layton
2023-10-30 23:34 ` ronnie sahlberg
2023-10-24 14:24 ` Jeff Layton
2023-10-24 19:06 ` Jeff Layton
2023-10-24 19:40 ` Linus Torvalds
2023-10-24 20:19 ` Jeff Layton
2023-10-31 10:26 ` Christian Brauner
2023-10-31 13:55 ` Jeff Layton
2023-10-19 22:00 ` Thomas Gleixner
2023-10-19 22:41 ` Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 3/9] timekeeping: add new debugfs file to count multigrain timestamps Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 4/9] fs: add infrastructure for " Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 5/9] fs: have setattr_copy handle multigrain timestamps appropriately Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 6/9] xfs: switch to multigrain timestamps Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 7/9] ext4: " Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 8/9] btrfs: convert " Jeff Layton
2023-10-18 17:41 ` [PATCH RFC 9/9] tmpfs: add support for " Jeff Layton
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