diff options
Diffstat (limited to 'fs/xfs/xfs_bmap.h')
| -rw-r--r-- | fs/xfs/xfs_bmap.h | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/fs/xfs/xfs_bmap.h b/fs/xfs/xfs_bmap.h index 6ff70cda451..9f3e3a836d1 100644 --- a/fs/xfs/xfs_bmap.h +++ b/fs/xfs/xfs_bmap.h @@ -54,12 +54,23 @@ typedef struct xfs_bmap_free_item /* * Header for free extent list. + * + * xbf_low 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. */ typedef struct xfs_bmap_free { xfs_bmap_free_item_t *xbf_first; /* list of to-be-free extents */ int xbf_count; /* count of items on list */ - int xbf_low; /* kludge: alloc in low mode */ + int xbf_low; /* alloc in low mode */ } xfs_bmap_free_t; #define XFS_BMAP_MAX_NMAP 4 |