From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: david@fromorbit.com
Cc: Christoph Hellwig <hch@infradead.org>, xfs@oss.sgi.com
Subject: RFCv4+ WIP rollup of XFS reverse-mapping, reflink, and dedupe support
Date: Fri, 22 Jan 2016 17:31:30 -0800 [thread overview]
Message-ID: <20160123013130.GC5496@birch.djwong.org> (raw)
Hi all,
I pushed all the current reflink/rmap code to github. This time there are some
incompat disk format changes, since I added a separate CoW extent size hint per
discussion with Dave; and moved the reflink inode flag out of the way of the
DAX inode flag.
The last patch in the kernel tree tries to record extents being used to
satisfy CoW requests in the refcount btree so that if we crash we can later
find those extents (which are no longer pending) and free them. I'm abandoning
the use of EFIs to auto-zap the pending extents because I don't want the log
size to be an upper bound on the number of CoW IOs we can have in flight at a
given time.
Furthermore, I think EFIs will interact badly with cowextsize -- since we must
maintain an EFI for every extent that is alloc'd but not yet mapped, a writeout
in the middle of the extent when the rest of the extent isn't yet dirty
requires us to log an EFD to kill the first EFI and then log two more EFIs. If
the log happens to be /full/ (of pending EFIs) when we do this, we won't have
space to log the extra EFIs and boom. All this assumes that we can relog EFIs
to avoid crashing the log head into the tail, which we can't at the moment.
Avoid running reflink and rmap at the same time -- there are some xfs_buf
deadlocks that I haven't sorted out yet. xfs/821 fails until I figure out
a permanent solution to per-AG pools.
On the plus side, there's now an inheritable CoW extent size hint so that we
can fight fragmentation, and a lot more testing of IO errors and fragmentation
problems that crop up with CoW.
I'll rebase on upstream after the merge window closes on Sunday.
https://github.com/djwong/linux/commits/for-dave
https://github.com/djwong/xfsprogs/tree/for-dave
https://github.com/djwong/xfstests/tree/for-dave
https://github.com/djwong/xfs-documentation/tree/for-dave
--D
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next reply other threads:[~2016-01-23 1:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-23 1:31 Darrick J. Wong [this message]
2016-01-28 13:16 ` RFCv4+ WIP rollup of XFS reverse-mapping, reflink, and dedupe support Christoph Hellwig
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