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From: Christoph Hellwig <hch@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org, vishal.l.verma@intel.com,
	bfoster@redhat.com, xfs@oss.sgi.com
Subject: Re: [PATCH 08/47] xfs: support btrees with overlapping intervals for keys
Date: Tue, 2 Aug 2016 05:03:54 -0700	[thread overview]
Message-ID: <20160802120354.GA2667@infradead.org> (raw)
In-Reply-To: <20160801191126.GE8590@birch.djwong.org>

On Mon, Aug 01, 2016 at 12:11:26PM -0700, Darrick J. Wong wrote:
> > > +/*
> > > + * In-core key that holds both low and high keys for overlapped btrees.
> > > + * The two keys are packed next to each other on disk, so do the same
> > > + * in memory.  Preserve the existing xfs_btree_key as a single key to
> > > + * avoid the mental model breakage that would happen if we passed a
> > > + * bigkey into a function that operates on a single key.
> > > + */
> > > +union xfs_btree_bigkey {
> > > +	struct xfs_bmbt_key		bmbt;
> > > +	xfs_bmdr_key_t			bmbr;	/* bmbt root block */
> > > +	xfs_alloc_key_t			alloc;
> > > +	struct xfs_inobt_key		inobt;
> > > +};
> > 
> > I don't understand the purpose of this union at all, and the comment
> > seems misleading.  Compared to union xfs_btree_key the only difference
> > seems to be that xfs_btree_bigkey is missing the
> > 'struct xfs_rmap_key rmap' member.  How does that enable us to holds
> 
> I think you might be missing a later patch, wherein we add the rmap
> stuff to the btree structures, which expands bigkey to look like this:

Yeah, I was stuck in the middle of tree.  I still think the bigkey
is a very bad idea.  There are only 7 place left that actually
allocate storage for a "union xfs_btree_key".  Everything else uses
fancy pointer arithmetics to get them out of a disk buffer:

 - xfs_btree_lookup
 - xfs_btree_get_leaf_keys_overlapped
 - xfs_btree_update_keys
 - xfs_btree_lshift
 - xfs_btree_rshift
 - xfs_btree_simple_query_range
 - xfs_btree_overlapped_query_range

So just adding the rmap to union xfs_btree_key would simplify things
and remove a potential pitfall at the cost of just a little bit
more stack usage.  And at least of the
init_high_key_from_rec/init_key_from_rec we could probably replace
two on-stack xfs_btree_keys with a single new, bigger xfs_btree_key.

> union xfs_btree_key {
> 	struct xfs_bmbt_key		bmbt;
> 	xfs_bmdr_key_t			bmbr;	/* bmbt root block */
> 	xfs_alloc_key_t			alloc;
> 	struct xfs_inobt_key		inobt;
> 	struct xfs_rmap_key		rmap[2];
> 	struct xfs_refcount_key		refc;
> };
> 
> This gives us the storage we want and avoids casts, but it still
> doesn't fix the problem that sometimes we want to create a key pointer
> to just the high fields and treat that as a pointer.

Where does that problem occur?  I don't quite understand how having
the bigger structure is a problem if we don't want to initialize all
of it.

  reply	other threads:[~2016-08-02 12:05 UTC|newest]

Thread overview: 121+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-21  4:55 [PATCH v7 00/47] xfs: add reverse mapping support Darrick J. Wong
2016-07-21  4:56 ` [PATCH 01/47] vfs: fix return type of ioctl_file_dedupe_range Darrick J. Wong
2016-08-01  6:33   ` Christoph Hellwig
2016-07-21  4:56 ` [PATCH 02/47] vfs: support FS_XFLAG_REFLINK and FS_XFLAG_COWEXTSIZE Darrick J. Wong
2016-08-01  6:33   ` Christoph Hellwig
2016-07-21  4:56 ` [PATCH 03/47] xfs: fix attr shortform structure alignment on cris Darrick J. Wong
2016-07-26 16:36   ` Brian Foster
2016-08-01  6:34   ` Christoph Hellwig
2016-07-21  4:56 ` [PATCH 04/47] xfs: fix locking of the rt bitmap/summary inodes Darrick J. Wong
2016-07-26 16:36   ` Brian Foster
2016-07-28 18:58     ` Darrick J. Wong
2016-08-01  6:34   ` Christoph Hellwig
2016-07-21  4:56 ` [PATCH 05/47] xfs: set *stat=1 after iroot realloc Darrick J. Wong
2016-07-26 16:36   ` Brian Foster
2016-08-01  6:35   ` Christoph Hellwig
2016-07-21  4:56 ` [PATCH 06/47] xfs: during btree split, save new block key & ptr for future insertion Darrick J. Wong
2016-07-26 16:36   ` Brian Foster
2016-08-01  6:37   ` Christoph Hellwig
2016-07-21  4:56 ` [PATCH 07/47] xfs: add function pointers for get/update keys to the btree Darrick J. Wong
2016-07-26 19:09   ` Brian Foster
2016-07-28 19:13     ` Darrick J. Wong
2016-07-28 19:46   ` [PATCH v2 " Darrick J. Wong
2016-08-01 15:57     ` Brian Foster
2016-08-01 17:54       ` Darrick J. Wong
2016-08-01  6:39   ` [PATCH " Christoph Hellwig
2016-08-01 17:33     ` Darrick J. Wong
2016-08-02 12:23       ` Christoph Hellwig
2016-08-03  0:12         ` Darrick J. Wong
2016-07-21  4:56 ` [PATCH 08/47] xfs: support btrees with overlapping intervals for keys Darrick J. Wong
2016-08-01  6:48   ` Christoph Hellwig
2016-08-01 19:11     ` Darrick J. Wong
2016-08-02 12:03       ` Christoph Hellwig [this message]
2016-08-03  3:29         ` Darrick J. Wong
2016-08-02 14:04       ` Brian Foster
2016-08-03  1:06         ` Dave Chinner
2016-08-01 17:47   ` Brian Foster
2016-08-01 19:18     ` Darrick J. Wong
2016-07-21  4:56 ` [PATCH 09/47] xfs: introduce interval queries on btrees Darrick J. Wong
2016-08-01  8:00   ` Christoph Hellwig
2016-07-21  4:57 ` [PATCH 10/47] xfs: refactor btree owner change into a separate visit-blocks function Darrick J. Wong
2016-08-01  6:50   ` Christoph Hellwig
2016-07-21  4:57 ` [PATCH 11/47] xfs: move deferred operations into a separate file Darrick J. Wong
2016-08-01  7:08   ` Christoph Hellwig
2016-08-01  8:02   ` Christoph Hellwig
2016-08-02 22:39     ` Dave Chinner
2016-08-03  9:16       ` Christoph Hellwig
2016-08-03 22:57         ` Dave Chinner
2016-08-04 16:00           ` Christoph Hellwig
2016-08-04 23:44             ` Dave Chinner
2016-08-02 17:30   ` Brian Foster
2016-07-21  4:57 ` [PATCH 12/47] xfs: add tracepoints for the deferred ops mechanism Darrick J. Wong
2016-07-21  4:57 ` [PATCH 13/47] xfs: clean up typedef usage in the EFI/EFD handling code Darrick J. Wong
2016-08-01  7:09   ` Christoph Hellwig
2016-07-21  4:57 ` [PATCH 14/47] xfs: enable the xfs_defer mechanism to process extents to free Darrick J. Wong
2016-08-01  7:09   ` Christoph Hellwig
2016-08-02 17:30   ` Brian Foster
2016-07-21  4:57 ` [PATCH 15/47] xfs: rework xfs_bmap_free callers to use xfs_defer_ops Darrick J. Wong
2016-08-02 17:30   ` Brian Foster
2016-07-21  4:57 ` [PATCH 16/47] xfs: change xfs_bmap_{finish, cancel, init, free} -> xfs_defer_* Darrick J. Wong
2016-08-02 17:30   ` Brian Foster
2016-08-02 20:47     ` Darrick J. Wong
2016-07-21  4:57 ` [PATCH 17/47] xfs: rename flist/free_list to dfops Darrick J. Wong
2016-08-02 17:30   ` Brian Foster
2016-07-21  4:58 ` [PATCH 18/47] xfs: refactor redo intent item processing Darrick J. Wong
2016-08-01  8:10   ` Christoph Hellwig
2016-08-02 20:35     ` Darrick J. Wong
2016-08-02 18:47   ` Brian Foster
2016-07-21  4:58 ` [PATCH 19/47] xfs: add tracepoints and error injection for deferred extent freeing Darrick J. Wong
2016-08-02 18:48   ` Brian Foster
2016-08-02 20:24     ` Darrick J. Wong
2016-08-02 21:38       ` Brian Foster
2016-08-02 22:43         ` Darrick J. Wong
2016-07-21  4:58 ` [PATCH 20/47] xfs: increase XFS_BTREE_MAXLEVELS to fit the rmapbt Darrick J. Wong
2016-08-02 18:48   ` Brian Foster
2016-08-02 20:06     ` Darrick J. Wong
2016-08-02 21:38       ` Brian Foster
2016-07-21  4:58 ` [PATCH 21/47] xfs: introduce rmap btree definitions Darrick J. Wong
2016-07-21  4:58 ` [PATCH 22/47] xfs: add rmap btree stats infrastructure Darrick J. Wong
2016-07-21  4:58 ` [PATCH 23/47] xfs: rmap btree add more reserved blocks Darrick J. Wong
2016-07-21  4:58 ` [PATCH 24/47] xfs: add owner field to extent allocation and freeing Darrick J. Wong
2016-07-21  4:58 ` [PATCH 25/47] xfs: introduce rmap extent operation stubs Darrick J. Wong
2016-07-21  4:58 ` [PATCH 26/47] xfs: define the on-disk rmap btree format Darrick J. Wong
2016-07-21  4:59 ` [PATCH 27/47] xfs: add rmap btree growfs support Darrick J. Wong
2016-07-21  4:59 ` [PATCH 28/47] xfs: rmap btree transaction reservations Darrick J. Wong
2016-07-21  4:59 ` [PATCH 29/47] xfs: rmap btree requires more reserved free space Darrick J. Wong
2016-07-21  4:59 ` [PATCH 30/47] xfs: add rmap btree operations Darrick J. Wong
2016-07-21  4:59 ` [PATCH 31/47] xfs: support overlapping intervals in the rmap btree Darrick J. Wong
2016-07-21  4:59 ` [PATCH 32/47] xfs: teach rmapbt to support interval queries Darrick J. Wong
2016-07-21  4:59 ` [PATCH 33/47] xfs: add tracepoints for the rmap functions Darrick J. Wong
2016-07-21  4:59 ` [PATCH 34/47] xfs: add an extent to the rmap btree Darrick J. Wong
2016-07-21  4:59 ` [PATCH 35/47] xfs: remove an extent from " Darrick J. Wong
2016-07-21  5:00 ` [PATCH 36/47] xfs: convert unwritten status of reverse mappings Darrick J. Wong
2016-08-03  2:00   ` Dave Chinner
2016-07-21  5:00 ` [PATCH 37/47] xfs: add rmap btree insert and delete helpers Darrick J. Wong
2016-07-21  5:00 ` [PATCH 38/47] xfs: create rmap update intent log items Darrick J. Wong
2016-08-01  7:12   ` Christoph Hellwig
2016-08-01 18:08     ` Darrick J. Wong
2016-07-21  5:00 ` [PATCH 39/47] xfs: log rmap intent items Darrick J. Wong
2016-07-21  5:00 ` [PATCH 40/47] xfs: enable the xfs_defer mechanism to process rmaps to update Darrick J. Wong
2016-07-21  5:00 ` [PATCH 41/47] xfs: propagate bmap updates to rmapbt Darrick J. Wong
2016-07-21  5:00 ` [PATCH 42/47] xfs: add rmap btree geometry feature flag Darrick J. Wong
2016-07-21  5:00 ` [PATCH 43/47] xfs: add rmap btree block detection to log recovery Darrick J. Wong
2016-07-21  5:00 ` [PATCH 44/47] xfs: disable XFS_IOC_SWAPEXT when rmap btree is enabled Darrick J. Wong
2016-07-21  5:01 ` [PATCH 45/47] xfs: don't update rmapbt when fixing agfl Darrick J. Wong
2016-07-21  5:01 ` [PATCH 46/47] xfs: enable the rmap btree functionality Darrick J. Wong
2016-07-21  5:01 ` [PATCH 47/47] xfs: introduce the XFS_IOC_GETFSMAP ioctl Darrick J. Wong
2016-07-23  4:28   ` [PATCH v2 " Darrick J. Wong
2016-08-03 19:45 ` [PATCH v7 00/47] xfs: add reverse mapping support Mark Fasheh
2016-08-03 20:55   ` Darrick J. Wong
2016-08-04  0:58     ` Darrick J. Wong
2016-08-04  2:18       ` Mark Fasheh
2016-08-04 15:48         ` Darrick J. Wong
2016-08-04 23:50           ` Dave Chinner
2016-08-05  0:49             ` Darrick J. Wong
2016-08-05  7:01             ` Artem Bityutskiy
2016-08-05  7:22               ` Darrick J. Wong
2016-08-05 10:49               ` Dave Chinner
2016-08-05 11:57                 ` Artem Bityutskiy
2016-08-05 22:26                   ` Dave Chinner
2016-08-05 18:36             ` Mark Fasheh
2016-08-05 22:39               ` Dave Chinner

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