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([2600:1700:e72:80a0:fcac:2b0b:1f40:7f1a]) by smtp.gmail.com with ESMTPSA id z7-20020a81a247000000b00559ec10f245sm677549ywg.103.2023.05.05.13.45.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 05 May 2023 13:45:36 -0700 (PDT) Message-ID: <4ce3ff5f-e7cd-f604-f5da-66939be7d314@github.com> Date: Fri, 5 May 2023 16:45:35 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.10.1 Subject: Re: [PATCH v2 0/2] pack-bitmap: boundary-based bitmap traversalt To: Taylor Blau Cc: git@vger.kernel.org, Jeff King , Junio C Hamano References: <6c8d9142-9013-f3f0-0619-b3780b86b6ab@github.com> Content-Language: en-US From: Derrick Stolee In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On 5/5/2023 2:46 PM, Taylor Blau wrote: > On Fri, May 05, 2023 at 01:59:31PM -0400, Derrick Stolee wrote: >> On 5/5/2023 1:27 PM, Taylor Blau wrote: >>> Here is a reroll of my series to implement a boundary-based bitmap >>> traversal algorithm that I worked on towards the end of 2021 with Peff. >>> >>> The algorithm is unchanged from the last version, but the implementation >>> has been made much more straightforward, thanks to a very helpful >>> suggestion from Stolee. >>> >>> Instead of hackily trying to write down all of the UNINTERESTING commits >>> between the tips and boundary within limit_list(), we can just perform a >>> commit-only walk, which will give us the set of commits that we need. >> >> Something that didn't seem to get attention in this version was buried >> deep in the commentary of my high-level review [1]: > > Oops, sorry, I definitely missed this unintentionally and did not mean > to ignore it. I had to dig deep to find it, even after knowing it was in there somewhere, so I'm not upset it didn't happen this version. >>> For these reasons, I'm surprised that this patch completely replaces >>> the old algorithm for the new one. I would prefer to see a config >>> option that enables this new algorithm. It would be safer to deploy >>> that way, too. >> >> I still think it would be nice to keep the two algorithms for at least >> a little while instead of completely removing the old one. Let's gather >> some more evidence and get more reps in with the new algorithm before >> making it the new default. I could imagine a scenario where someone >> really wants to spend the extra time to make sure none of the objects >> reachable from the UNINTERESTING commits are included in the output of >> this diff. >> >> [1] https://lore.kernel.org/git/a143150d-7cf5-c697-0e48-0f7af1c6de8f@github.com/ > > Hmm. I'm not opposed to keeping the old algorithm around, though I > wonder what the configuration option would look like here. I imagine > that we don't want to support the old algorithm indefinitely, though. > > Perhaps something like `pack.useBoundaryBitmapTraversal` (implied by > `feature.experimental`), defaulting to "false", and then eventually > "true"? This name makes sense to me. Including it in feature.experimental right away seems like a good idea. Incrementing it to "true" by default after a single release would make sense, too, since the performance benefits are so clear. Just important to have that emergency toggle. Thanks, -Stolee