From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: "Theodore Y. Ts'o" <tytso@mit.edu>,
Eric Biggers <ebiggers@kernel.org>,
Linux Filesystem Development List
<linux-fsdevel@vger.kernel.org>,
Ext4 Developers List <linux-ext4@vger.kernel.org>,
linux-f2fs-devel@lists.sourceforge.net,
linux-xfs@vger.kernel.org
Subject: Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
Date: Fri, 13 Mar 2020 09:39:13 +1100 [thread overview]
Message-ID: <20200312223913.GL10776@dread.disaster.area> (raw)
In-Reply-To: <20200312143445.GA19160@infradead.org>
On Thu, Mar 12, 2020 at 07:34:45AM -0700, Christoph Hellwig wrote:
> On Thu, Mar 12, 2020 at 11:07:17AM +1100, Dave Chinner wrote:
> > > That's true, but when the timestamps were originally modified,
> > > dirty_inode() will be called with flag == I_DIRTY_TIME, which will
> > > *not* be a no-op; which is to say, XFS will force the timestamps to be
> > > updated on disk when the timestamps are first dirtied, because it
> > > doesn't support I_DIRTY_TIME.
> >
> > We log the initial timestamp change, and then ignore timestamp
> > updates until the dirty time expires and the inode is set
> > I_DIRTY_SYNC via __mark_inode_dirty_sync(). IOWs, on expiry, we have
> > time stamps that may be 24 hours out of date in memory, and they
> > still need to be flushed to the journal.
> >
> > However, your change does not mark the inode dirtying on expiry
> > anymore, so...
> >
> > > So I think we're fine.
> >
> > ... we're not fine. This breaks XFS and any other filesystem that
> > relies on a I_DIRTY_SYNC notification to handle dirty time expiry
> > correctly.
>
> I haven't seen the original mail this replies to,
The original problem was calling mark_inode_dirty_sync() on expiry
during inode writeback was causing the inode to be put back on the
dirty inode list and so ext4 was flushing it twice - once on expiry
and once 5 seconds later on the next background writeback pass.
This is a problem that XFS does not have because it does not
implement ->write_inode...
> but if we could
> get the lazytime expirty by some other means (e.g. an explicit
> callback), XFS could opt out of all the VFS inode tracking again,
> which would simplify a few things.
Yes, that would definitely make things simpler for XFS, and it would
also solve the problem that the generic lazytime expiry code has....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2020-03-12 22:39 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-06 0:45 lazytime causing inodes to remain dirty after sync? Eric Biggers
2020-03-07 2:00 ` [PATCH] writeback: avoid double-writing the inode on a lazytime expiration Theodore Ts'o
2020-03-11 3:20 ` Eric Biggers
2020-03-11 12:57 ` Theodore Y. Ts'o
2020-03-12 0:07 ` Dave Chinner
2020-03-12 14:34 ` Christoph Hellwig
2020-03-12 22:39 ` Dave Chinner [this message]
2020-03-20 2:46 ` Theodore Y. Ts'o
2020-03-20 2:52 ` [PATCH 1/2] " Theodore Ts'o
2020-03-20 2:52 ` [PATCH 2/2] writeback, xfs: call dirty_inode() with I_DIRTY_TIME_EXPIRED when appropriate Theodore Ts'o
2020-03-23 17:58 ` Theodore Y. Ts'o
2020-03-24 8:37 ` Christoph Hellwig
2020-03-24 18:43 ` Theodore Y. Ts'o
2020-03-25 9:20 ` [PATCH 1/2] writeback: avoid double-writing the inode on a lazytime expiration Christoph Hellwig
2020-03-25 15:21 ` Theodore Y. Ts'o
2020-03-25 15:47 ` Darrick J. Wong
2020-03-11 23:54 ` [PATCH] " Dave Chinner
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