On Thu, Oct 06, 2016 at 06:02:25PM -0700, Darrick J. Wong wrote: > > Ok, kind of nasty with all of the various paths through get_blocks(), > > but hopefully that dies off with buffer heads. > > It's possible Christoph might have further cleanup patches for reflink > that fix this? <shrug> I do. It's stuck on not getting one of the corner cases right at the moment, and I had to take a break from it yesterday to go insane, but I hope I'll be able to post it soon. > Yes, that would have been another way to implement it. I think I > finally see your point about using the delalloc mechanism -- since we've > converted the buffered write path to iomap and therefore know exactly > how much userspace wants to write in both buffered and directio cases, > we could just allocate the cow extent right then and there, skipping the > overhead of writing a delalloc reservation and then changing it. > > For buffered writes, though, it's nice to be able to use the DA > mechanism so that we can ask the allocator for as big of an extent as we > have contiguous dirty pages. Hm. I guess for directio then we could > just fill in the holes directly and convert any delalloc reservations > that happened already to be there, which requires only a single loop. > > Will ponder this some more, thx for the pushback. :) Having spent a lot of the time with the COW and non-COW I/O path lately here is my 2 cents: delalloc for the buffered write path inherently make sense and mirrors what we do for non-COW I/O. I have patches to rewrite parts of how we do it, but I see no reason to change that we are doing delayed allocations. For the direct I/O path there is absolutely no point in doing delayed allocation and I plan to get rid of them for the next merge window. -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
