From: Jeff Layton <jlayton@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>,
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>,
Dave Chinner <david@fromorbit.com>, 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: Wed, 18 Oct 2023 17:52:43 -0400 [thread overview]
Message-ID: <5f96e69d438ab96099bb67d16b77583c99911caa.camel@kernel.org> (raw)
In-Reply-To: <CAHk-=wiKJgOg_3z21Sy9bu+3i_34S86r8fd6ngvJpZDwa-ww8Q@mail.gmail.com>
On Wed, 2023-10-18 at 14:31 -0700, Linus Torvalds wrote:
> On Wed, 18 Oct 2023 at 13:47, Jeff Layton <jlayton@kernel.org> wrote:
> >
> > > old_ctime_nsec &= ~I_CTIME_QUERIED;
> > > if (ts64.tv_nsec > old_ctime_nsec + inode->i_sb->s_time_gran)
> > > return ts64;
> > >
> >
> > Does that really do what you expect here? current_time will return a
> > value that has already been through timestamp_truncate.
>
> Yeah, you're right.
>
> I think you can actually remove the s_time_gran addition. Both the
> old_ctime_nsec and the current ts64,tv_nsec are already rounded, so
> just doing
>
> if (ts64.tv_nsec > old_ctime_nsec)
> return ts64;
>
> would already guarantee that it's different enough.
>
Yep, and that's basically what inode_set_ctime_current does (though it
does a timespec64 comparison).
> > current_mgtime is calling ktime_get_real_ts64, which is an existing
> > interface that does not take the global spinlock and won't advance the
> > global offset. That call should be quite cheap.
>
> Ahh, I did indeed mis-read that as the new one with the lock.
>
> I did react to the fact that is_mgtime(inode) itself is horribly
> expensive if it's not cached (following three quite possibly cold
> pointers), which was part of that whole "look at I_CTIME_QUERIED
> instead".
>
> I see the pointer chasing as a huge VFS timesink in all my profiles,
> although usually it's the disgusting security pointer (because selinux
> creates separate security nodes for each inode, even when the contents
> are often identical). So I'm a bit sensitive to "follow several
> pointers from 'struct inode'" patterns from looking at too many
> instruction profiles.
That's a very good point. I'll see if I can get rid of that (and maybe
some other mgtime flag checks) before I send the next version.
Back to your earlier point though:
Is a global offset really a non-starter? I can see about doing something
per-superblock, but ktime_get_mg_coarse_ts64 should be roughly as cheap
as ktime_get_coarse_ts64. I don't see the downside there for the non-
multigrain filesystems to call that.
On another note: maybe I need to put this behind a Kconfig option
initially too?
--
Jeff Layton <jlayton@kernel.org>
next prev parent reply other threads:[~2023-10-18 21:52 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 [this message]
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
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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