On Wed, Jul 28, 2010 at 11:19:57AM +0100, Steven Whitehouse wrote: > In case #1, I don't think there is any need to actually issue a flush > along with the barrier - the fs will always be correct in case of a (for > example) power failure and it is only the amount of data which might be > lost which depends on the write cache size. This is basically the same > for any local filesystem. For now we're mostly talking about removing the _ordering_ not the flushing. Eventually I'd like to relax some of the flushing requirements, too - but that is secondary priority. So for now I'm mostly interested if gfs2 relies on the ordering semantics from barriers. Given that it's been around for a while and primarily used on devices without any kind of barriers support I'm inclined it is, but I'd really prefer to get this from the horses mouth. > I have also made the assumption that a barrier issued from one node to > the shared device will affect I/O from all nodes equally. If that is not > the case, then the above will not apply and we must always flush in case > #3. There is absolutely no ordering vs other nodes. The volatile write cache if present is a per-target state so it will be flushed for all nodes. > Currently the code is also waiting for I/O to drain in cases #1 and #3 > as well as case #2 since it was simpler to implement all cases the same, > at least to start with. Aka gfs2 waits for the I/O completion by itself. That sounds like it is the answer to my original question. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
