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From: Derrick Stolee <stolee@gmail.com>
To: Taylor Blau <me@ttaylorr.com>, git@vger.kernel.org
Cc: peff@peff.net, dstolee@microsoft.com, szeder.dev@gmail.com,
	gitster@pobox.com
Subject: Re: [PATCH v3 12/14] commit-graph: add large-filters bitmap chunk
Date: Tue, 11 Aug 2020 17:11:49 -0400	[thread overview]
Message-ID: <4f487dca-a938-b4c4-8b77-a202209459cb@gmail.com> (raw)
In-Reply-To: <619e0c619dd12e2bea2b80c7d249ba66fe2a315c.1597178915.git.me@ttaylorr.com>

On 8/11/20 4:52 PM, Taylor Blau wrote:
> To allow using the existing bitmap code with 64-bit words, we write the
> data in network byte order from the 64-bit words. This means we also
> need to read the array from the commit-graph file by translating each
> word from network byte order using get_be64() when loading the commit
> graph. (Note that this *could* be delayed until first-use, but a later
> patch will rely on this being initialized early, so we assume the
> up-front cost when parsing instead of delaying initialization).

I don't think this is correct to do. This means that every commit-graph
load will load the entire large bloom filter chunk into memory before
allowing a single commit to be read from the graph.

In the case of a very large commit-graph (> 1 million commits), this
would cause a significant initial cost that is not necessarily needed
for anything. For example, "git log -1" will be delayed by this action.

If I understand correctly, this bloom_large bitmap is only used when
writing Bloom filters. At that point, reading the entire bitmap from
disk into memory is inexpensive compared to the time saved by the
feature.

> @@ -429,6 +430,24 @@ struct commit_graph *parse_commit_graph(struct repository *r,
>  				graph->bloom_filter_settings->bits_per_entry = get_be32(data + chunk_offset + 8);
>  			}
>  			break;
> +
> +		case GRAPH_CHUNKID_BLOOMLARGE:
> +			if (graph->chunk_bloom_large_filters)
> +				chunk_repeated = 1;
> +			else if (r->settings.commit_graph_read_changed_paths) {

This is guarded against commitGraph.readChangedPaths, which is good,
but that's not enough to claim that we need the bloom_large bitmap
in this process.

> +				size_t alloc = get_be64(chunk_lookup + 4) - chunk_offset - sizeof(uint32_t);

If we store this inside the commit_graph struct, we can save this
size for later so...

> +				graph->chunk_bloom_large_filters = data + chunk_offset + sizeof(uint32_t);
> +				graph->bloom_filter_settings->max_changed_paths = get_be32(data + chunk_offset);

...this portion can be done only when we are about to read from the
bitmap.

> +				if (alloc) {
> +					size_t j;
> +					graph->bloom_large = bitmap_word_alloc(alloc);
> +
> +					for (j = 0; j < graph->bloom_large->word_alloc; j++)
> +						graph->bloom_large->words[j] = get_be64(
> +							graph->chunk_bloom_large_filters + j * sizeof(eword_t));
> +				}



> +			}
> +			break;
>  		}
>  
>  		if (chunk_repeated) {
> @@ -443,7 +462,9 @@ struct commit_graph *parse_commit_graph(struct repository *r,
>  		/* We need both the bloom chunks to exist together. Else ignore the data */
>  		graph->chunk_bloom_indexes = NULL;
>  		graph->chunk_bloom_data = NULL;
> +		graph->chunk_bloom_large_filters = NULL;
>  		FREE_AND_NULL(graph->bloom_filter_settings);
> +		bitmap_free(graph->bloom_large);

Perhaps this bitmap_free() needs a check to see if we
initialized it (with my recommended lazy-loading), but
maybe not?

>  	}
>  
>  	hashcpy(graph->oid.hash, graph->data + graph->data_len - graph->hash_len);
> @@ -932,6 +953,20 @@ struct tree *get_commit_tree_in_graph(struct repository *r, const struct commit
>  	return get_commit_tree_in_graph_one(r, r->objects->commit_graph, c);
>  }
>  
> +static int get_bloom_filter_large_in_graph(struct commit_graph *g,
> +					   const struct commit *c)
> +{
> +	uint32_t graph_pos = commit_graph_position(c);
> +	if (graph_pos == COMMIT_NOT_FROM_GRAPH)
> +		return 0;
> +
> +	while (g && graph_pos < g->num_commits_in_base)
> +		g = g->base_graph;
> +
> +	if (!(g && g->bloom_large))
> +		return 0;

Here is where we can check if the size of the chunk is
non-zero and if the g->bloom_large bitmap is uninitialized.
Since we are caring about this information, it is now time
to do the network-byte transition of the full bitmap.

> +	return bitmap_get(g->bloom_large, graph_pos - g->num_commits_in_base);
> +}
>  
Thanks,
-Stolee

  reply	other threads:[~2020-08-11 21:11 UTC|newest]

Thread overview: 117+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-03 18:57 [PATCH 00/10] more miscellaneous Bloom filter improvements Taylor Blau
2020-08-03 18:57 ` [PATCH 01/10] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-08-04  7:24   ` Jeff King
2020-08-04 20:08     ` Taylor Blau
2020-08-03 18:57 ` [PATCH 02/10] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-08-03 18:57 ` [PATCH 03/10] t4216: use an '&&'-chain Taylor Blau
2020-08-03 18:57 ` [PATCH 04/10] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-08-03 18:57 ` [PATCH 05/10] commit-graph: respect 'commitgraph.readChangedPaths' Taylor Blau
2020-08-03 18:57 ` [PATCH 06/10] commit-graph.c: sort index into commits list Taylor Blau
2020-08-04 12:31   ` Derrick Stolee
2020-08-04 20:10     ` Taylor Blau
2020-08-03 18:57 ` [PATCH 07/10] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-08-03 18:59   ` Taylor Blau
2020-08-04 12:57   ` Derrick Stolee
2020-08-03 18:57 ` [PATCH 08/10] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-08-04 13:00   ` Derrick Stolee
2020-08-04 20:12     ` Taylor Blau
2020-08-03 18:57 ` [PATCH 09/10] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-08-03 18:57 ` [PATCH 10/10] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-08-04 13:03   ` Derrick Stolee
2020-08-04 20:14     ` Taylor Blau
2020-08-05 17:01 ` [PATCH v2 00/14] more miscellaneous Bloom filter improvements Taylor Blau
2020-08-05 17:01   ` [PATCH v2 01/14] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-08-05 17:02   ` [PATCH v2 02/14] t4216: use an '&&'-chain Taylor Blau
2020-08-05 17:02   ` [PATCH v2 03/14] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-08-05 17:02   ` [PATCH v2 04/14] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-08-05 17:02   ` [PATCH v2 05/14] commit-graph: respect 'commitGraph.readChangedPaths' Taylor Blau
2020-08-05 17:02   ` [PATCH v2 06/14] commit-graph.c: store maximum changed paths Taylor Blau
2020-08-05 17:02   ` [PATCH v2 07/14] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-08-05 17:02   ` [PATCH v2 08/14] bloom: use provided 'struct bloom_filter_settings' Taylor Blau
2020-08-05 17:02   ` [PATCH v2 09/14] bloom/diff: properly short-circuit on max_changes Taylor Blau
2020-08-05 17:02   ` [PATCH v2 10/14] commit-graph.c: sort index into commits list Taylor Blau
2020-08-05 17:02   ` [PATCH v2 11/14] csum-file.h: introduce 'hashwrite_be64()' Taylor Blau
2020-08-05 17:02   ` [PATCH v2 12/14] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-08-05 21:01     ` Junio C Hamano
2020-08-05 21:17       ` Taylor Blau
2020-08-05 22:21         ` Junio C Hamano
2020-08-05 22:25           ` Taylor Blau
2020-08-11 13:48             ` Taylor Blau
2020-08-11 18:59               ` Junio C Hamano
2020-08-05 17:03   ` [PATCH v2 13/14] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-08-05 17:03   ` [PATCH v2 14/14] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-08-11 20:51 ` [PATCH v3 00/14] more miscellaneous Bloom filter improvements Taylor Blau
2020-08-11 20:51   ` [PATCH v3 01/14] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-08-11 21:18     ` SZEDER Gábor
2020-08-11 21:21       ` Taylor Blau
2020-08-11 21:27         ` SZEDER Gábor
2020-08-11 21:34           ` Taylor Blau
2020-08-11 23:55             ` SZEDER Gábor
2020-08-12 11:48               ` Derrick Stolee
2020-08-14 20:17                 ` Taylor Blau
2020-08-11 20:51   ` [PATCH v3 02/14] t4216: use an '&&'-chain Taylor Blau
2020-08-11 20:51   ` [PATCH v3 03/14] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-08-11 20:51   ` [PATCH v3 04/14] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-08-11 20:51   ` [PATCH v3 05/14] commit-graph: respect 'commitGraph.readChangedPaths' Taylor Blau
2020-08-11 20:51   ` [PATCH v3 06/14] commit-graph.c: store maximum changed paths Taylor Blau
2020-08-11 20:51   ` [PATCH v3 07/14] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-08-11 20:51   ` [PATCH v3 11/14] csum-file.h: introduce 'hashwrite_be64()' Taylor Blau
2020-08-11 20:51   ` [PATCH v3 08/14] bloom: use provided 'struct bloom_filter_settings' Taylor Blau
2020-08-11 20:51   ` [PATCH v3 09/14] bloom/diff: properly short-circuit on max_changes Taylor Blau
2020-08-11 20:52   ` [PATCH v3 10/14] commit-graph.c: sort index into commits list Taylor Blau
2020-08-11 20:52   ` [PATCH v3 12/14] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-08-11 21:11     ` Derrick Stolee [this message]
2020-08-11 21:18       ` Taylor Blau
2020-08-11 22:05         ` Taylor Blau
2020-08-19 13:35     ` SZEDER Gábor
2020-09-02 20:23       ` Taylor Blau
2020-09-01 14:35     ` SZEDER Gábor
2020-09-02 20:40       ` Taylor Blau
2020-08-11 20:52   ` [PATCH v3 13/14] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-08-19  9:56     ` SZEDER Gábor
2020-09-02 21:02       ` Taylor Blau
2020-08-11 20:52   ` [PATCH v3 14/14] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-08-12 11:49     ` SZEDER Gábor
2020-08-14 20:20       ` Taylor Blau
2020-08-17 22:50         ` SZEDER Gábor
2020-09-02 21:03           ` Taylor Blau
2020-08-12 12:29     ` Derrick Stolee
2020-08-14 20:10       ` Taylor Blau
2020-08-18 22:23     ` SZEDER Gábor
2020-09-03 16:35       ` Taylor Blau
2020-08-19  8:20     ` SZEDER Gábor
2020-09-03 16:42       ` Taylor Blau
2020-09-04  8:50         ` SZEDER Gábor
2020-09-01 14:36     ` SZEDER Gábor
2020-09-03 18:49       ` Taylor Blau
2020-09-03 21:45   ` [PATCH v3 00/14] more miscellaneous Bloom filter improvements Junio C Hamano
2020-09-03 22:33     ` Taylor Blau
2020-09-03 22:45 ` [PATCH v4 " Taylor Blau
2020-09-03 22:46   ` [PATCH v4 01/14] commit-graph: introduce 'get_bloom_filter_settings()' Taylor Blau
2020-09-03 22:46   ` [PATCH v4 02/14] t4216: use an '&&'-chain Taylor Blau
2020-09-03 22:46   ` [PATCH v4 03/14] commit-graph: pass a 'struct repository *' in more places Taylor Blau
2020-09-03 22:46   ` [PATCH v4 04/14] t/helper/test-read-graph.c: prepare repo settings Taylor Blau
2020-09-03 22:46   ` [PATCH v4 05/14] commit-graph: respect 'commitGraph.readChangedPaths' Taylor Blau
2020-09-03 22:46   ` [PATCH v4 06/14] commit-graph.c: store maximum changed paths Taylor Blau
2020-09-03 22:46   ` [PATCH v4 07/14] bloom: split 'get_bloom_filter()' in two Taylor Blau
2020-09-05 17:22     ` Jakub Narębski
2020-09-05 17:38       ` Taylor Blau
2020-09-05 17:50         ` Jakub Narębski
2020-09-05 18:01           ` Taylor Blau
2020-09-05 18:18             ` Jakub Narębski
2020-09-05 18:38               ` Taylor Blau
2020-09-05 18:55                 ` Taylor Blau
2020-09-05 19:04                   ` SZEDER Gábor
2020-09-05 19:49                     ` Taylor Blau
2020-09-06 21:52                       ` Junio C Hamano
2020-09-03 22:46   ` [PATCH v4 08/14] bloom: use provided 'struct bloom_filter_settings' Taylor Blau
2020-09-03 22:46   ` [PATCH v4 09/14] bloom/diff: properly short-circuit on max_changes Taylor Blau
2020-09-03 22:46   ` [PATCH v4 10/14] commit-graph.c: sort index into commits list Taylor Blau
2020-09-03 22:46   ` [PATCH v4 11/14] csum-file.h: introduce 'hashwrite_be64()' Taylor Blau
2020-09-04 20:18     ` René Scharfe
2020-09-04 20:22       ` Taylor Blau
2020-09-03 22:46   ` [PATCH v4 12/14] commit-graph: add large-filters bitmap chunk Taylor Blau
2020-09-03 22:46   ` [PATCH v4 13/14] commit-graph: rename 'split_commit_graph_opts' Taylor Blau
2020-09-04 15:20     ` Taylor Blau
2020-09-03 22:47   ` [PATCH v4 14/14] builtin/commit-graph.c: introduce '--max-new-filters=<n>' Taylor Blau
2020-09-04 14:39   ` [PATCH v4 00/14] more miscellaneous Bloom filter improvements Derrick Stolee

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