On Mon, 2008-11-24 at 09:03 +0000, David Woodhouse wrote: > On Mon, 2008-11-24 at 07:52 +0900, James Bottomley wrote: > > On Sun, 2008-11-23 at 13:39 +0000, David Woodhouse wrote: > > > > We don't attempt to put non-contiguous ranges into a single TRIM yet. > > > > > > We don't even merge contiguous ranges -- I still need to fix the > > > elevators to stop writes crossing writes, > > > > I don't think we want to do that ... it's legal if the write isn't a > > barrier and it will inhibit merging. That may be just fine for a SSD, > > but it's not for spinning media since they get better performance out of > > merged writes. > > No, I just mean writes _to the same sector_. At the moment, we happily > let those cross each other in the queue. That's legal ... if you want the ordering to matter, you either wait or insert a barrier. > We do notice this situation and preserve the ordering if the two > requests cover _precisely_ the same range, but _overlapping_ writes may > happen in any order. > > We should fix that, and it's only for _that_ purpose that I'm saying we > treat writes and discards as identical. And then we can drop the barrier > flag on discards. It's not a bug ... but changing it might be feasible ... as long as it doesn't affect write performance too much (which I don't think it will), since it is in the critical path. > And _then_ we can think about special cases which let us merge > non-contiguous discards. I still think that treating discards as a special command from the outset is the better way forwards. James -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
