-
Dave Chinner authored
FSX on 512 byte block size filesystems has been failing for some time with corrupted data. The fault dates back to the change in the writeback data integrity algorithm that uses a mark-and-sweep approach to avoid data writeback livelocks. Unfortunately, a side effect of this mark-and-sweep approach is that each page will only be written once for a data integrity sync, and there is a condition in writeback in XFS where a page may require two writeback attempts to be fully written. As a result of the high level change, we now only get a partial page writeback during the integrity sync because the first pass through writeback clears the mark left on the page index to tell writeback that the page needs writeback.... The cause is writing a partial page in the clustering code. This can happen when a mapping boundary falls in the middle of a page - we end up writing back the first part of the page that the mapping covers, but then never revisit the page to have the remainder mapped and written. The fix is simple - if the mapping boundary falls inside a page, then simple abort clustering without touching the page. This means that the next ->writepage entry that write_cache_pages() will make is the page we aborted on, and xfs_vm_writepage() will map all sections of the page correctly. This behaviour is also optimal for non-data integrity writes, as it results in contiguous sequential writeback of the file rather than missing small holes and having to write them a "random" writes in a future pass. With this fix, all the fsx tests in xfstests now pass on a 512 byte block size filesystem on a 4k page machine. Signed-off-by:
Dave Chinner <dchinner@redhat.com> Reviewed-by:
Brian Foster <bfoster@redhat.com> Signed-off-by:
Ben Myers <bpm@sgi.com>
49b137cb