From: Dave Chinner <david@fromorbit.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 5/5] xfs: introduce an always_cow mode
Date: Fri, 21 Sep 2018 07:23:57 +1000 [thread overview]
Message-ID: <20180920212357.GN27618@dastard> (raw)
In-Reply-To: <20180920201702.GN20086@magnolia>
On Thu, Sep 20, 2018 at 01:17:02PM -0700, Darrick J. Wong wrote:
> On Thu, Sep 20, 2018 at 04:42:20PM +0200, Christoph Hellwig wrote:
> > When the (debug-only) always_cow module parameter is set, we will always
> > write out place, even if the file is not reflinked. In addition to being
> > a useful debug aid this prepares for modes where we must always write
> > out of place. An example for that is the upcoming support for atomic
> > overwrites.
....
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > index b25ea7a3a0e7..a893f6d65ff0 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -129,6 +129,11 @@
> > * ioend, the better.
> > */
> >
> > +#ifdef DEBUG
> > +bool xfs_always_cow;
> > +module_param_named(always_cow, xfs_always_cow, bool, 0644);
> > +#endif
>
> I would have expected this to end up in /proc/sys/fs/xfs/always_cow
> along with all the other behavior knobs, but I guess this is a debugging
> thing...?
sys/fs/xfs/debug/always_cow is the place for this if it is truly a
global debug option. However, that's probably not the best way to
enable this sort of debug for people with XFS root filesystems
trying to test XFS filesystems. I suspect it should be a per-mount
configuration (i.e. /sys/fs/xfs/<dev>/debug/always_cow)
However, this mode of operation seems like it is going to form the
basis of other per-filesystem features, so it would be good to know
how/if those features make use of this always_cow mode or are
controlled by some other set of knobs first.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2018-09-21 3:09 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-20 14:42 more reflink fixes & debug Christoph Hellwig
2018-09-20 14:42 ` [PATCH 1/5] xfs: cancel COW blocks before swapext Christoph Hellwig
2018-09-20 20:04 ` Darrick J. Wong
2018-09-27 15:07 ` Brian Foster
2018-09-30 22:50 ` Christoph Hellwig
2018-10-01 11:03 ` Brian Foster
2018-09-20 14:42 ` [PATCH 2/5] xfs: skip delalloc COW blocks in xfs_reflink_end_cow Christoph Hellwig
2018-09-20 20:22 ` Darrick J. Wong
2018-09-20 14:42 ` [PATCH 3/5] xfs: fix fork selection in xfs_find_trim_cow_extent Christoph Hellwig
2018-09-20 14:42 ` [PATCH 4/5] xfs: print dangling delalloc extents Christoph Hellwig
2018-09-20 20:06 ` Darrick J. Wong
2018-09-27 15:07 ` Brian Foster
2018-09-20 14:42 ` [PATCH 5/5] xfs: introduce an always_cow mode Christoph Hellwig
2018-09-20 20:17 ` Darrick J. Wong
2018-09-20 21:23 ` Dave Chinner [this message]
2018-09-21 5:23 ` Christoph Hellwig
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