On Fri, Feb 06, 2015 at 02:52:56PM -0500, Brian Foster wrote: > The block allocator supports various arguments to tweak block allocation > behavior and set allocation requirements. The sparse inode chunk feature > introduces a new requirement not supported by the current arguments. > Sparse inode allocations must convert or merge into an inode record that > describes a fixed length chunk (64 inodes x inodesize). Full inode chunk > allocations by definition always result in valid inode records. Sparse > chunk allocations are smaller and the associated records can refer to > blocks not owned by the inode chunk. This model can result in invalid > inode records in certain cases. > > For example, if a sparse allocation occurs near the start of an AG, the > aligned inode record for that chunk might refer to agbno 0. If an > allocation occurs towards the end of the AG and the AG size is not > aligned, the inode record could refer to blocks beyond the end of the > AG. While neither of these scenarios directly result in corruption, they > both insert invalid inode records and at minimum cause repair to > complain, are unlikely to merge into full chunks over time and set land > mines for other areas of code. > > To guarantee sparse inode chunk allocation creates valid inode records, > support the ability to specify an agbno range limit for > XFS_ALLOCTYPE_NEAR_BNO block allocations. The min/max agbno's are > specified in the allocation arguments and limit the block allocation > algorithms to that range. The starting 'agbno' hint is clamped to the > range if the specified agbno is out of range. If no sufficient extent is > available within the range, the allocation fails. For backwards > compatibility, the min/max fields can be initialized to 0 to disable > range limiting (e.g., equivalent to min=0,max=agsize). > > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx> Seems sane on reading the implementation. I'll see if I still think that way when I read the code that uses it ;) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
