From: Dave Chinner <david@fromorbit.com>
To: Brian Foster <bfoster@redhat.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>, linux-xfs@vger.kernel.org
Subject: Re: [RFC PATCH 0/14] xfs: Towards thin provisioning aware filesystems
Date: Mon, 6 Nov 2017 09:50:28 +1100 [thread overview]
Message-ID: <20171105225028.GB5858@dastard> (raw)
In-Reply-To: <20171103113622.GB19974@bfoster.bfoster>
On Fri, Nov 03, 2017 at 07:36:23AM -0400, Brian Foster wrote:
> On Thu, Nov 02, 2017 at 07:47:40PM -0700, Darrick J. Wong wrote:
> > FWIW the way I've been modelling this patch series in my head is that we
> > format an arbitrarily large filesystem (m_LBA_size) address space on a
> > thinp, feed statfs an "adjusted" size (m_usable_size)i which restricts
> > how much space we can allocate, and now growfs increases or decreases
> > the adjusted size without having to relocate anything or mess with the
> > address space. If the adjusted size ever exceeds the address space
> > size, then we tack on more AGs like we've always done. From that POV,
> > there's no need to physically shrink (i.e. relocate) anything (and we
> > can leave that for later/never).
[...]
> For example, suppose we had an absolute crude, barebones implementation
> of physical shrink right now that basically trimmmed the amount of space
> from the end of the fs iff those AGs were completely empty and otherwise
> returned -EBUSY. There is no other userspace support, etc. As such, this
> hypothetical feature is extremely limited to being usable immediately
> after a growfs and thus probably has no use case other than "undo my
> accidental growfs."
>
> If we had that right now, _then_ what would the logical shrink interface
> look like?
Absolutely no different to what I'm proposing we do right now. That
is, the behaviour of the "shrink to size X" ioctl is determined by
the feature bit in the superblock. Hence if the thinspace feature
is set we do a thin shrink, and if it is not set we do a physical
shrink. i.e. grow/shrink behaviour is defined by the kernel
implementation, not the user or the interface.
As it is, I still can't see a use case or compelling reason for
physically shrinking a thin filesystem. What's the use case that
leads you to think that we need to physically shrink a thin
filesystem, Brian? Let's get that on the table first, rather than
waste time discussing hypothetical what-if's....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2017-11-05 22:50 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 8:33 [RFC PATCH 0/14] xfs: Towards thin provisioning aware filesystems Dave Chinner
2017-10-26 8:33 ` [PATCH 01/14] xfs: factor out AG header initialisation from growfs core Dave Chinner
2017-10-26 8:33 ` [PATCH 02/14] xfs: convert growfs AG header init to use buffer lists Dave Chinner
2017-10-26 8:33 ` [PATCH 03/14] xfs: factor ag btree reoot block initialisation Dave Chinner
2017-10-26 8:33 ` [PATCH 04/14] xfs: turn ag header initialisation into a table driven operation Dave Chinner
2017-10-26 8:33 ` [PATCH 05/14] xfs: make imaxpct changes in growfs separate Dave Chinner
2017-10-26 8:33 ` [PATCH 06/14] xfs: separate secondary sb update in growfs Dave Chinner
2017-10-26 8:33 ` [PATCH 07/14] xfs: rework secondary superblock updates " Dave Chinner
2017-10-26 8:33 ` [PATCH 08/14] xfs: move various type verifiers to common file Dave Chinner
2017-10-26 8:33 ` [PATCH 09/14] xfs: split usable space from block device size Dave Chinner
2017-10-26 8:33 ` [PATCH 10/14] xfs: hide reserved metadata space from users Dave Chinner
2017-10-26 8:33 ` [PATCH 11/14] xfs: bump XFS_IOC_FSGEOMETRY to v5 structures Dave Chinner
2017-10-26 8:33 ` [PATCH 12/14] xfs: convert remaingin xfs_sb_version_... checks to bool Dave Chinner
2017-10-26 16:03 ` Darrick J. Wong
2017-10-26 8:33 ` [PATCH 13/14] xfs: add suport for "thin space" filesystems Dave Chinner
2017-10-26 8:33 ` [PATCH 14/14] xfs: add growfs support for changing usable blocks Dave Chinner
2017-10-26 11:30 ` Amir Goldstein
2017-10-26 12:48 ` Dave Chinner
2017-10-26 13:32 ` Amir Goldstein
2017-10-27 10:26 ` Amir Goldstein
2017-10-26 11:09 ` [RFC PATCH 0/14] xfs: Towards thin provisioning aware filesystems Amir Goldstein
2017-10-26 12:35 ` Dave Chinner
2017-11-01 22:31 ` Darrick J. Wong
2017-10-30 13:31 ` Brian Foster
2017-10-30 21:09 ` Dave Chinner
2017-10-31 4:49 ` Amir Goldstein
2017-10-31 22:40 ` Dave Chinner
2017-10-31 11:24 ` Brian Foster
2017-11-01 0:45 ` Dave Chinner
2017-11-01 14:17 ` Brian Foster
2017-11-01 23:53 ` Dave Chinner
2017-11-02 11:25 ` Brian Foster
2017-11-02 23:30 ` Dave Chinner
2017-11-03 2:47 ` Darrick J. Wong
2017-11-03 11:36 ` Brian Foster
2017-11-05 22:50 ` Dave Chinner [this message]
2017-11-06 13:01 ` Brian Foster
2017-11-06 21:20 ` Dave Chinner
2017-11-07 11:28 ` Brian Foster
2017-11-03 11:26 ` Brian Foster
2017-11-03 12:19 ` Amir Goldstein
2017-11-06 1:16 ` Dave Chinner
2017-11-06 9:48 ` Amir Goldstein
2017-11-06 21:46 ` Dave Chinner
2017-11-07 5:30 ` Amir Goldstein
2017-11-05 23:51 ` Dave Chinner
2017-11-06 13:07 ` Brian Foster
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