From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qt1-f182.google.com (mail-qt1-f182.google.com [209.85.160.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C1F162BEC43 for ; Wed, 24 Jun 2026 12:14:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782303271; cv=none; b=TS9LBhrmDKEMdmf6eLnxI2u1eZDE2YxP400n2dlFw5Bpcb8hlDR5ihrUiWTIWQANQgTGtoxGATgdSsD2aHKWrqYlC8x9YaZNjqmAUojqqbKBAYPDOEn1eZjBxANcUdrDBIp7mlriEaS6F/p5FKO3c5IMpuTJqKEW3cvvi+VRGfw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782303271; c=relaxed/simple; bh=HvDCLc11wTtO6sC5Eyv4JivN/7K1wCAjLB/fV3SNHB4=; h=Message-Id:In-Reply-To:References:From:Date:Subject:Content-Type: MIME-Version:To:Cc; b=KJ+NYBN0hnW5vWCqH/cHwDP/8qtuOInjIwzltaTLd/c6Z/jjgvw8mdTkUyH5uDvphdCLzInqhr15vuynqMgWKcS4dgkr9dhh3bXyl2Wa5CfwDddIbocMkyoNl87rTYNpgvcQ75VNPSdZ9QPLP3IRSO0CDuSxYookms7ejj9mzNU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=VgxSRlyK; arc=none smtp.client-ip=209.85.160.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="VgxSRlyK" Received: by mail-qt1-f182.google.com with SMTP id d75a77b69052e-519eedc30a3so9270581cf.1 for ; Wed, 24 Jun 2026 05:14:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1782303269; x=1782908069; darn=vger.kernel.org; h=cc:to:mime-version:content-transfer-encoding:fcc:subject:date:from :references:in-reply-to:message-id:from:to:cc:subject:date :message-id:reply-to; bh=Jym4wQPdpjUlZF6TDZSCkYtnTM6W7Lda2iurHZercQw=; b=VgxSRlyKHPcvQ63Xroe6LonUvnAauYhc4dwgn9QKfFRqqxhdBxrc9IkTvd6w5x3+5e pRghD9UuBdzOlsz0iRcwMRoF//LAehoDy73GXh/WnbqWNXadhhql1uFjQzKPS2ATcVq4 UcOCWdVw0pMUiHrNf++sl2pBDcC4PuttJ2bol1TK2zidBykeW6rvImFkB204BIFBBMhQ dOaMlD5p1iaOHLU1HR5BDDWMgSdYxme5PXkr9nfYqFZa9xa1BaIUUEcFogtQ4NzzU3CY EUN2UjHAyiBH9HsdJx2TsqyTjObjUodFY0OAtacUYwLdvEEerT3y+8mDBGG7itx08Emz GEZA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1782303269; x=1782908069; h=cc:to:mime-version:content-transfer-encoding:fcc:subject:date:from :references:in-reply-to:message-id:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=Jym4wQPdpjUlZF6TDZSCkYtnTM6W7Lda2iurHZercQw=; b=OrDqjs30aYni8TGWOuXT/4wGaXwcq5Wz8t5CLZn+w8r4Ghqwhd1EedylkGjnYdKg1o Uljz5vIVm/R94eHz+oLS5a4PCsVdGPASjgxLCulaCoelLer2nFPsg90TOsbdaBsFnwHH SExdjcnGk2yXIwxFN/slC7j7RcQbJdYbP/daqJJgSUc+RllvS6rcPq/0Ka+OjF5VOHuk QrYSWQQV8Pd4TSZv2uS+dj8CCU0MbULwQdv/hHptKSe/ohGLirD8/M44apK89FYur4a0 8wtUuPLW8kkP8LyGBj6GN9tNuq850OXNLAFy1u/zkpgRenTSQ6/oFsOvlb6ZbiI6+ttT 8nKA== X-Gm-Message-State: AOJu0YxMp0f+0H8MJmY1DeoGFmEtV6x0LKbPZXM0i765kPPWxA8/waAD hl6bVMOAqSxbPCe41os0SWv/Gf/a1r5q9IpIusZB+I5JTyPaanuI/OSZZiqWnNsd X-Gm-Gg: AfdE7cnnerwPNJVjPFzEwRoB69YDskCzXsm3OAMFRIgRgu60s83Cgh7W9KNzHNwGaPM B3B4bY6Q0nQA86vjx9x11t7C6MDi0Tl64228SNVz8Wae6v2AyrTQInWybixupUS8a9t9bFKUnKK fQuRJ8R8qkgUHEKxYVfd0wF7K6WrzhDFU57UKfuApvSET/+JwOsXc86p5YjdgbAot/H6TwHJvIC MvWnpp8lMuMsTLNWZ/iEq5X31XR43fZ8cNi+QJcmF+FsfxwgmSPwnNwsIoAMbB+jkNz/rW37pdA mguuD2suqcOKGM6TW7ZXBHxKaVRzg+SjX/vBAPefcjWdaJnfROmr2l1hWubx6MDI/kq81NY8zJB Q04WhrOcxNqk06TIZwI68BFXm7IewAw8GcXWW5Nk9HxosLK8VG410p3L9u20qPz01NcGRn765+O Iemp2b0fJYjZWPoJw= X-Received: by 2002:a05:622a:1dcf:b0:516:ce43:f4ee with SMTP id d75a77b69052e-51a61b46c76mr47026361cf.20.1782303268571; Wed, 24 Jun 2026 05:14:28 -0700 (PDT) Received: from [127.0.0.1] ([40.116.92.119]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-51a515c72c1sm47323091cf.10.2026.06.24.05.14.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Jun 2026 05:14:27 -0700 (PDT) Message-Id: In-Reply-To: References: From: "Kristofer Karlsson via GitGitGadget" Date: Wed, 24 Jun 2026 12:14:13 +0000 Subject: [PATCH v2 7/7] commit-reach: terminate merge-base walk when one paint side is exhausted Fcc: Sent Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 To: git@vger.kernel.org Cc: Derrick Stolee , Elijah Newren , Kristofer Karlsson , Kristofer Karlsson From: Kristofer Karlsson Add an early termination check to paint_down_to_common() using the per-side counters introduced earlier. Once the walk enters the finite-generation region, terminate early when one side's exclusive count drops to zero -- no new merge-base can form without both paint sides meeting. The check also waits for pending_merge_bases to reach zero, ensuring all merge-base candidates have been dequeued and recorded before exiting. The INFINITY gate ensures correctness: commits without a commit-graph entry have GENERATION_NUMBER_INFINITY and are ordered by commit date, which is not topologically reliable. The optimization only fires once the walk enters the finite-generation region where ordering guarantees hold. Step counts measured with trace2 on git.git with commit-graph: merge-base --all v2.0.0 v2.55.0-rc1: before: 72264 steps after: 44589 steps merge-base --all v2.55.0-rc1 v2.55.0-rc1~5: before: 110 steps after: 7 steps Helped-by: Derrick Stolee Helped-by: Elijah Newren Signed-off-by: Kristofer Karlsson --- .../technical/paint-down-to-common.adoc | 17 ++++++++++++ commit-reach.c | 27 ++++++++++++++----- t/t6600-test-reach.sh | 4 +-- 3 files changed, 39 insertions(+), 9 deletions(-) diff --git a/Documentation/technical/paint-down-to-common.adoc b/Documentation/technical/paint-down-to-common.adoc index 0f4e1892a5..983dfcf233 100644 --- a/Documentation/technical/paint-down-to-common.adoc +++ b/Documentation/technical/paint-down-to-common.adoc @@ -94,6 +94,9 @@ ends when one of the following conditions holds: 1. The queue is empty. 2. The queue contains only stale entries. + 3. Side exhaustion: no pure PARENT1 or pure PARENT2 commits + remain in the queue, no pending merge-base candidates exist, + and the walk has entered the finite-generation region. Stale entry condition ~~~~~~~~~~~~~~~~~~~~~ @@ -104,6 +107,20 @@ existing candidates by proving one is an ancestor of another, but `remove_redundant()` handles that as a post-processing step, so it is safe to exit early. +Side-exhaustion condition +~~~~~~~~~~~~~~~~~~~~~~~~~ +A new merge-base requires commits from both sides to meet. When one +side's exclusive counter reaches zero and there are no pending +merge-base candidates, no future traversal step can produce a new +candidate. + +This optimization only activates in the finite-generation region +where topological ordering holds. In that region, children are +always visited before parents, so paint flags are final at visit +time and an exhausted side cannot reappear. In the INFINITY region, +commit-date ordering can violate this guarantee, so the check is +skipped. + Related documentation --------------------- diff --git a/commit-reach.c b/commit-reach.c index e0d9874f99..f79d0b64d6 100644 --- a/commit-reach.c +++ b/commit-reach.c @@ -133,17 +133,30 @@ static void paint_queue_put(struct paint_state *state, static struct commit *paint_queue_get(struct paint_state *state) { - struct commit *commit; + struct commit *commit = prio_queue_get(&state->queue); - if (!state->p1_count && !state->p2_count && - !state->pending_merge_bases) + if (!commit) return NULL; - commit = prio_queue_get(&state->queue); - if (commit) { - commit->object.flags &= ~ENQUEUED; - paint_count_update(state, commit->object.flags, -1); + commit->object.flags &= ~ENQUEUED; + + if (!state->pending_merge_bases) { + if (!state->p1_count && !state->p2_count) + return NULL; + /* + * Side exhaustion: a new merge-base can only form + * when both PARENT1-only and PARENT2-only commits + * remain in the queue. In the finite-generation + * region the queue is ordered topologically, so + * no future step can add paint to visited commits + * and an exhausted side cannot reappear. + */ + if ((!state->p1_count || !state->p2_count) && + commit_graph_generation(commit) < GENERATION_NUMBER_INFINITY) + return NULL; } + + paint_count_update(state, commit->object.flags, -1); return commit; } diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh index c1109fb42f..03175befb3 100755 --- a/t/t6600-test-reach.sh +++ b/t/t6600-test-reach.sh @@ -332,12 +332,12 @@ test_expect_success 'merge-base --all commit-walk steps' ' cp commit-graph-full .git/objects/info/commit-graph && GIT_TRACE2_EVENT="$(pwd)/trace-full.txt" \ git merge-base --all commit-9-9 commit-9-1 >actual && - test_trace2_data paint_down_to_common steps 80 actual && - test_trace2_data paint_down_to_common steps 81