On Fri, Nov 08, 2024 at 08:51:31AM -0700, Keith Busch wrote: > On Fri, Nov 08, 2024 at 03:18:52PM +0100, Christoph Hellwig wrote: > > We're not really duplicating much. Writing sequential is pretty easy, > > and tracking reclaim units separately means you need another tracking > > data structure, and either that or the LBA one is always going to be > > badly fragmented if they aren't the same. > > You're getting fragmentation anyway, which is why you had to implement > gc. You're just shifting who gets to deal with it from the controller to > the host. The host is further from the media, so you're starting from a > disadvantage. The host gc implementation would have to be quite a bit > better to justify the link and memory usage necessary for the copies > (...queue a copy-offload discussion? oom?). But the filesystem knows which blocks are actually in use. Sending TRIM/DISCARD information to the drive at block-level granularity hasn't worked out so well in the past. So the drive is the one at a disadvantage because it has to copy blocks which aren't actually in use. I like the idea of using copy-offload though.
