On Thu, Feb 17, 2011 at 04:50:57PM +1100, NeilBrown wrote: > > Hi Andrew (and others) > I wonder if you would review the following for me and comment. Please send think in this area through -fsdevel next time, thanks! > There are two cases when we call flush_disk. > In one, the device has disappeared (check_disk_change) so any > data will hold becomes irrelevant. > In the oter, the device has changed size (check_disk_size_change) > so data we hold may be irrelevant. > > In both cases it makes sense to discard any 'clean' buffers, > so they will be read back from the device if needed. Does it? If the device has disappeared we can't read them back anyway. If the device has resized to a smaller size the same is true about those buffers that have gone away, and if it has resized to a larger size invalidating anything doesn't make sense at all. I think this area needs more love than a quick kill_dirty hackjob. > In the former case it makes sense to discard 'dirty' buffers > as there will never be anywhere safe to write the data. In the > second case it *does*not* make sense to discard dirty buffers > as that will lead to file system corruption when you simply enlarge > the containing devices. Doing anything like this at the buffer cache layer or inode cache layer doesn't make any sense. If a device goes away or shrinks below the filesystem size the filesystem simply needs to be shut down and in te former size the admin needs to start a manual repair. Trying to do any botch jobs in lower layer never works in practice. For now I think the best short term fix is to simply revert commit 608aeef17a91747d6303de4df5e2c2e6899a95e8 "Call flush_disk() after detecting an online resize." -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
