From patchwork Wed Nov 11 19:44:24 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Taylor Blau X-Patchwork-Id: 11898431 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BB41C5517A for ; Wed, 11 Nov 2020 19:44:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AD6D7207F7 for ; Wed, 11 Nov 2020 19:44:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ttaylorr-com.20150623.gappssmtp.com header.i=@ttaylorr-com.20150623.gappssmtp.com header.b="m5KIE8l9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727874AbgKKTo2 (ORCPT ); Wed, 11 Nov 2020 14:44:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55172 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727868AbgKKTo2 (ORCPT ); Wed, 11 Nov 2020 14:44:28 -0500 Received: from mail-qv1-xf42.google.com (mail-qv1-xf42.google.com [IPv6:2607:f8b0:4864:20::f42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 29008C0613D1 for ; Wed, 11 Nov 2020 11:44:28 -0800 (PST) Received: by mail-qv1-xf42.google.com with SMTP id ec16so1539788qvb.0 for ; Wed, 11 Nov 2020 11:44:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ttaylorr-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Bh/sxgDmzH4yBz/lJLa665MnoIXLK85KXlMvWajUJ6Y=; b=m5KIE8l95MqfdcP4zM8oN2qi4NPIudIQHITuK26m+qOv9FCBaBsxcCgBuAC+cL28xn twqvIAtEIn1LiRRbYYUoP9Ch4dexjJEgyRmlqzcyiBjgSUqPKga2xYm69KrEqAfKoaAm k8iY1fgBgTvGBlyL8xhKBpTAmduBpADZrOqnEd7qQK5+Zht+kykZa/9nAnzz8z9FsAWG Sn252zNpIZsfEgv7jN2d+tjLq8a4huRgyakssTNIYBk1+F6lJ4Ws6ngeSjvUWYdb7ZVE 93qtBuJJ4IAtLTkUpJRnS6/dZB1Xo71PJdhrL2Mjd0KSc6/BdzfJscuN7lbVeWwcLwrQ xDkQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Bh/sxgDmzH4yBz/lJLa665MnoIXLK85KXlMvWajUJ6Y=; b=dsubNK9rLAzh34BuADbtJMyX7dk+0IDHTT9GIfwNB4yuu4SyMmLyTUbdrUfEFpRL1U kblSsV8S7Nc1ALKevhHtp7phHD/ckJaIae15xit2UtsXmmva5b6HV1jHijOpYM1d7qaK zOqrynIcFaVA3YzbOVy0OCXEO9gvakiwZgOFhyYkT7IBKtavuQMSHrZXQH9/nQDLIbA1 HvVMT+MCvmhqpZo8q6LQVjbW/YJa8ykEuu1dk9AHwKSP0kiC58mggkvgiC2MSiwDh9Ga 8R8QXUmE1wkO8dRtjixrdSD07kQEw1rB4eDRd1n7bCiGGNauAQdceeE5QzgLnD7IUOax pEhw== X-Gm-Message-State: AOAM532YABZcNsUZxH1pbTR8ubH4zIqBuCglNAlDnfgq6Il4okOTFg7A yIG9chPm1JIChWnbRflLBUnyxE0Sqvpm2rVH X-Google-Smtp-Source: ABdhPJzuE6eNmzSE8q1hfUY2RBIGW51tqYBJ+hluvk38cqDfOi1hQU2PaTTp0Xd4Ff79HA+8T31a1g== X-Received: by 2002:a0c:db8c:: with SMTP id m12mr3321359qvk.11.1605123867051; Wed, 11 Nov 2020 11:44:27 -0800 (PST) Received: from localhost ([2605:9480:22e:ff10:7ccc:9a51:1ad:2057]) by smtp.gmail.com with ESMTPSA id y3sm2946813qto.2.2020.11.11.11.44.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2020 11:44:26 -0800 (PST) Date: Wed, 11 Nov 2020 14:44:24 -0500 From: Taylor Blau To: git@vger.kernel.org Cc: dstolee@microsoft.com, gitster@pobox.com, peff@peff.net Subject: [PATCH 22/23] pack-bitmap-write: relax unique rewalk condition Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Derrick Stolee The previous commits improved the bitmap computation process for very long, linear histories with many refs by removing quadratic growth in how many objects were walked. The strategy of computing "intermediate commits" using bitmasks for which refs can reach those commits partitioned the poset of reachable objects so each part could be walked exactly once. This was effective for linear histories. However, there was a (significant) drawback: wide histories with many refs had an explosion of memory costs to compute the commit bitmasks during the exploration that discovers these intermediate commits. Since these wide histories are unlikely to repeat walking objects, the benefit of walking objects multiple times was not expensive before. But now, the commit walk *before computing bitmaps* is incredibly expensive. In an effort to discover a happy medium, this change reduces the walk for intermediate commits to only the first-parent history. This focuses the walk on how the histories converge, which still has significant reduction in repeat object walks. It is still possible to create quadratic behavior in this version, but it is probably less likely in realistic data shapes. Here is some data taken on a fresh clone of the kernel: | runtime (sec) | peak heap (GB) | | | | | from | with | from | with | | scratch | existing | scratch | existing | -----------+---------+----------+---------+----------- original | 64.044 | 83.241 | 2.088 | 2.194 | last patch | 44.811 | 27.828 | 2.289 | 2.358 | this patch | 100.641 | 35.560 | 2.152 | 2.224 | Signed-off-by: Derrick Stolee Signed-off-by: Taylor Blau --- pack-bitmap-write.c | 14 +++++--------- t/t5310-pack-bitmaps.sh | 27 ++++++++++++++------------- 2 files changed, 19 insertions(+), 22 deletions(-) diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c index 37204b691c..b0493d971d 100644 --- a/pack-bitmap-write.c +++ b/pack-bitmap-write.c @@ -199,7 +199,7 @@ static void bitmap_builder_init(struct bitmap_builder *bb, { struct rev_info revs; struct commit *commit; - unsigned int i, num_maximal; + unsigned int i, num_maximal = 0; memset(bb, 0, sizeof(*bb)); init_bb_data(&bb->data); @@ -207,6 +207,7 @@ static void bitmap_builder_init(struct bitmap_builder *bb, reset_revision_walk(); repo_init_revisions(writer->to_pack->repo, &revs, NULL); revs.topo_order = 1; + revs.first_parent_only = 1; for (i = 0; i < writer->selected_nr; i++) { struct commit *c = writer->selected[i].commit; @@ -221,13 +222,12 @@ static void bitmap_builder_init(struct bitmap_builder *bb, add_pending_object(&revs, &c->object, ""); } - num_maximal = writer->selected_nr; if (prepare_revision_walk(&revs)) die("revision walk setup failed"); while ((commit = get_revision(&revs))) { - struct commit_list *p; + struct commit_list *p = commit->parents; struct bb_commit *c_ent; parse_commit_or_die(commit); @@ -235,16 +235,12 @@ static void bitmap_builder_init(struct bitmap_builder *bb, c_ent = bb_data_at(&bb->data, commit); if (c_ent->maximal) { - if (!c_ent->selected) { - bitmap_set(c_ent->commit_mask, num_maximal); - num_maximal++; - } - + num_maximal++; ALLOC_GROW(bb->commits, bb->commits_nr + 1, bb->commits_alloc); bb->commits[bb->commits_nr++] = commit; } - for (p = commit->parents; p; p = p->next) { + if (p) { struct bb_commit *p_ent = bb_data_at(&bb->data, p->item); int c_not_p, p_not_c; diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh index 33ef9a098d..68badd63cb 100755 --- a/t/t5310-pack-bitmaps.sh +++ b/t/t5310-pack-bitmaps.sh @@ -43,23 +43,24 @@ has_any () { # \| # * (base) # +# We only push bits down the first-parent history, which +# makes some of these commits unimportant! +# # The important part for the maximal commit algorithm is how # the bitmasks are extended. Assuming starting bit positions -# for master (bit 0) and other (bit 1), and some flexibility -# in the order that merge bases are visited, the bitmasks at -# the end should be: +# for master (bit 0) and other (bit 1), the bitmasks at the +# end should be: # # master: 1 (maximal, selected) # other: 01 (maximal, selected) -# octo-master: 1 -# octo-other: 01 -# merge-right: 111 (maximal) -# (l1): 111 -# (r1): 111 -# merge-left: 1101 (maximal) -# (l2): 11111 (maximal) -# (r2): 111101 (maximal) -# (base): 1111111 (maximal) +# (base): 11 (maximal) +# +# This complicated history was important for a previous +# version of the walk that guarantees never walking a +# commit multiple times. That goal might be important +# again, so preserve this complicated case. For now, this +# test will guarantee that the bitmaps are computed +# correctly, even with the repeat calculations. test_expect_success 'setup repo with moderate-sized history' ' test_commit_bulk --id=file 10 && @@ -113,7 +114,7 @@ test_expect_success 'full repack creates bitmaps' ' ls .git/objects/pack/ | grep bitmap >output && test_line_count = 1 output && grep "\"key\":\"num_selected_commits\",\"value\":\"106\"" trace && - grep "\"key\":\"num_maximal_commits\",\"value\":\"111\"" trace + grep "\"key\":\"num_maximal_commits\",\"value\":\"107\"" trace ' test_expect_success 'rev-list --test-bitmap verifies bitmaps' '