On Mon, Jan 17, 2011 at 08:37:08AM -0600, Geoffrey Wehrman wrote: > On Mon, Jan 17, 2011 at 04:18:28PM +1100, Dave Chinner wrote: > | On Fri, Jan 14, 2011 at 10:16:29PM -0600, Geoffrey Wehrman wrote: > | > On Sat, Jan 15, 2011 at 09:59:07AM +1100, Dave Chinner wrote: > | > | On Fri, Jan 14, 2011 at 10:40:16AM -0600, Geoffrey Wehrman wrote: > | > | > Also, I'm not saying using XFS_BMAPI_EXACT is feasible. I have a very > | > | > minimal understanding of the writepage code path. > | > | > | > | I think there are situations where this does make sense, but given > | > | the potential issues I'm not sure it is a solution that can be > | > | extended to the general case. A good discussion point on a different > | > | angle, though. ;) > | > > | > You've convinced me that XFS_BMAPI_EXACT is not the optimal solution. > | > > | > Upon further consideration, I do like your proposal to make delalloc > | > allocation more like an intent/done type operation. The compatibility > | > issues aren't all that bad. As long as the filesystem is unmounted > | > clean, there is no need for the next mount do log recovery and therefore > | > no need to have any knowledge of the new transactions. > | > | That is a good observation. If there is agreement that this a strong > | enough backwards compatibility guarantee (it's good enough for me), > | then I think that I will start to prototype this approach. > > I'm not sure how a version of XFS without the new log recovery code will > behave if it encounters a log with the new transactions. I assume it > will gracefully abort log recovery and fail the mount with the report of > a corrupt log. I have no objection with this compatibility guarantee. It will do the same as you describe for the old log recovery code, so there should be no new problems there. > | However, this does not solve the extsize allocation issues where we > | don't have dirty pages in the page cache covering parts of the > | delayed allocation extent so we still need a solution for that. I'm > | tending towards zeroing in .aio_write as the simplest solution > | because it doesn't cause buffer head/extent tree mapping mismatches, > | and it would use the above intent/done operations for crash > | resilience so there's no additional, rarely used code path to test > | through .writepage. Does that sound reasonable? > > Zeroing in .aio_write will create zeroed pages covering the entire > allocation, correct? Yes, though it only needs to zero the regions that the write does not cover itself - no need to zero what we're about to put data into. ;) Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
