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xfs: replace dop_low with transaction flag

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The dop_low field enables the low free space allocation mode when a
previous allocation has detected difficulty allocating blocks. It
has historically been part of the xfs_defer_ops structure, which
means if enabled, it remains enabled across a set of transactions
until the deferred operations have completed and the dfops is reset.

Now that the dfops is embedded in the transaction, we can save a bit
more space by using a transaction flag rather than a standalone
boolean. Drop the ->dop_low field and replace it with a transaction
flag that is set at the same points, carried across rolling
transactions and cleared on completion of deferred operations. This
essentially emulates the behavior of ->dop_low and so should not
change behavior.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Brian Foster
2018-08-01 07:20:31 -07:00
committed by Darrick J. Wong
parent ce356d6477
commit 1214f1cf66
8 changed files with 36 additions and 30 deletions
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12
fs/xfs/libxfs/xfs_shared.h
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@@ -64,6 +64,18 @@ void xfs_log_get_max_trans_res(struct xfs_mount *mp,
#define XFS_TRANS_RESERVE 0x20 /* OK to use reserved data blocks */
#define XFS_TRANS_NO_WRITECOUNT 0x40 /* do not elevate SB writecount */
#define XFS_TRANS_NOFS 0x80 /* pass KM_NOFS to kmem_alloc */
/*
* LOWMODE is used by the allocator to activate the lowspace algorithm - when
* free space is running low the extent allocator may choose to allocate an
* extent from an AG without leaving sufficient space for a btree split when
* inserting the new extent. In this case the allocator will enable the
* lowspace algorithm which is supposed to allow further allocations (such as
* btree splits and newroots) to allocate from sequential AGs. In order to
* avoid locking AGs out of order the lowspace algorithm will start searching
* for free space from AG 0. If the correct transaction reservations have been
* made then this algorithm will eventually find all the space it needs.
*/
#define XFS_TRANS_LOWMODE 0x100 /* allocate in low space mode */
/*
* Field values for xfs_trans_mod_sb.