On Mon, May 14, 2018 at 08:47:33AM -0400, Derrick Stolee wrote: > On 5/11/2018 2:03 PM, Jeff King wrote: > > Commit 941ba8db57 (Eliminate recursion in setting/clearing > > marks in commit list, 2012-01-14) used a clever double-loop > > to avoid allocations for single-parent chains of history. > > However, it did so only when following parents of parents > > (which was an uncommon case), and _always_ incurred at least > > one allocation to populate the list of pending parents in > > the first place. > > > > We can turn this into zero-allocation in the common case by > > iterating directly over the initial parent list, and then > > following up on any pending items we might have discovered. > > This change appears to improve performance, but I was unable to measure any > difference between this commit and the one ahead, even when merging > ds/generation-numbers (which significantly reduces the other costs). I was > testing 'git status' and 'git rev-list --boundary master...origin/master' in > the Linux repo with my copy of master 70,000+ commits behind origin/master. I think you'd want to go the other way: this is marking uninteresting commits, so you'd want origin/master..master, which would make those 70k commits uninteresting. I still doubt it will create that much difference, though. It's more or less saving a single malloc per commit we traverse. Certainly without the .commits file that's a drop in the bucket compared to inflating the object data, but I wouldn't be surprised if we end up with a few mallocs even after your patches. Anyway, thanks for poking at it. :) -Peff
