On Tue, Jun 25, 2019 at 09:15:23AM +1000, Dave Chinner wrote: > > So, uh, how much of a hit do we take for having to allocate a > > transaction for a file size extension? Particularly since we can > > combine those things now? > > Unless we are out of log space, the transaction allocation and free > should be largely uncontended and so it's just a small amount of CPU > usage. i.e it's a slab allocation/free and then lockless space > reservation/free. If we are out of log space, then we sleep waiting > for space - the issue really comes down to where it is better to > sleep in that case....
I see the general point, but we'll still have the same issue with unwritten extent conversion and cow completions, and I don't remember seeing any issue in that regard. And we'd hit exactly that case with random writes to preallocated or COW files, i.e. the typical image file workload.
