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From: Taylor Blau <me@ttaylorr.com>
To: Derrick Stolee <stolee@gmail.com>
Cc: Taylor Blau <me@ttaylorr.com>,
	git@vger.kernel.org, peff@peff.net, dstolee@microsoft.com,
	szeder.dev@gmail.com, gitster@pobox.com
Subject: Re: [PATCH v3 14/14] builtin/commit-graph.c: introduce '--max-new-filters=<n>'
Date: Fri, 14 Aug 2020 16:10:28 -0400	[thread overview]
Message-ID: <20200814201028.GC30103@syl.lan> (raw)
In-Reply-To: <ee5c0db0-6582-f039-96e1-be64ee4fe7a6@gmail.com>

On Wed, Aug 12, 2020 at 08:29:06AM -0400, Derrick Stolee wrote:
> On 8/11/2020 4:52 PM, Taylor Blau wrote:
> > Introduce a command-line flag and configuration variable to fill in the
> > 'max_new_filters' variable introduced by the previous patch.
> >
> > The command-line option '--max-new-filters' takes precedence over
> > 'commitGraph.maxNewFilters', which is the default value.
> > '--no-max-new-filters' can also be provided, which sets the value back
> > to '-1', indicating that an unlimited number of new Bloom filters may be
> > generated. (OPT_INTEGER only allows setting the '--no-' variant back to
> > '0', hence a custom callback was used instead).
> >
> > Signed-off-by: Taylor Blau <me@ttaylorr.com>
>
> ...
>
> > diff --git a/bloom.c b/bloom.c
> > index ed54e96e57..8d07209c6b 100644
> > --- a/bloom.c
> > +++ b/bloom.c
> > @@ -51,6 +51,21 @@ static int load_bloom_filter_from_graph(struct commit_graph *g,
> >  	else
> >  		start_index = 0;
> >
> > +	if ((start_index == end_index) &&
> > +	    (g->bloom_large && !bitmap_get(g->bloom_large, lex_pos))) {
> > +		/*
> > +		 * If the filter is zero-length, either (1) the filter has no
> > +		 * changes, (2) the filter has too many changes, or (3) it
> > +		 * wasn't computed (eg., due to '--max-new-filters').
> > +		 *
> > +		 * If either (1) or (2) is the case, the 'large' bit will be set
> > +		 * for this Bloom filter. If it is unset, then it wasn't
> > +		 * computed. In that case, return nothing, since we don't have
> > +		 * that filter in the graph.
> > +		 */
> > +		return 0;
> > +	}
> > +
>
> Here, you are creating a distinction between an "empty" filter and
> a "too large" filter at a place that I don't think is important.
>
> For instance, this code will be triggered by "git log -- <path>"
> but you only care about the filter being too large when writing the
> commit-graph. I think this check for a "too large" filter should
> instead be inside get_or_compute_bloom_filter(). I include a patch
> below that applies on top of tb/bloom-improvements that gets to
> my point (and how minor the issue might be).

That's a good point. I factored the lazy-loading out in basically the
same way that you did below, but didn't move this call out of
'load_bloom_filter_from_graph'. I think that you're right that this is
better at the calling end (replacing the 'start_index == end_index'
check with a '!filter->len' one instead).

I'm going to "ignore" this patch below since I (a) already have it
locally, and (b) would rather just do this correctly the first time than
introduce and subsequently fix a performance regression.

> Thanks,
> -Stolee
>
> --- >8 ---
>
> From 92a7a3d0f769fad7617426730cb97584a3d07794 Mon Sep 17 00:00:00 2001
> From: Derrick Stolee <dstolee@microsoft.com>
> Date: Wed, 12 Aug 2020 08:20:03 -0400
> Subject: [PATCH] commit-graph: lazy-load large Bloom filter bitmap
>
> The bloom_large bitmap in struct commit_graph is currently loaded
> immediately upon first parse of the commit-graph file (when the chunk
> exists). This is needed because the current implementation of
> get_bloom_filter_from_graph() is special-cased to return NULL when the
> filter is marked as "too large".
>
> This has a slight drawback: before we can read a single commit out of
> the commit-graph file, we need to load this entire chunk into memory.
> This happens even for commands that don't need changed-path Bloom
> filters, such as "git log -1".
>
> This "too large" information is only used when writing a commit-graph
> file, so we can delay the check for a large filter until after we check
> compute_if_not_present in get_or_compute_bloom_filter(). Also, place
> that lazy-load directly in the get_bloom_filter_large_in_graph() method,
> so we ensure it is ready when needed.
>
> This may be overkill. For a repository with one million commits, this
> filter size is approximately 125 *kilobytes* of data. My local
> measurements found that this took between 1 and 2 milliseconds to load
> into memory. Even for repositories with 10 million commits, this
> difference would not be noticeable for end-user commands.
>
> On the other hand, these handfuls of milliseconds could add up when
> running a hosting service using Git, so this extra effort is probably
> worth it.
>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  bloom.c        | 27 ++++++++-------------------
>  commit-graph.c | 30 +++++++++++++++++-------------
>  commit-graph.h |  8 ++++++++
>  3 files changed, 33 insertions(+), 32 deletions(-)
>
> diff --git a/bloom.c b/bloom.c
> index 8d07209c6b..6d0884fa19 100644
> --- a/bloom.c
> +++ b/bloom.c
> @@ -51,21 +51,6 @@ static int load_bloom_filter_from_graph(struct commit_graph *g,
>  	else
>  		start_index = 0;
>
> -	if ((start_index == end_index) &&
> -	    (g->bloom_large && !bitmap_get(g->bloom_large, lex_pos))) {
> -		/*
> -		 * If the filter is zero-length, either (1) the filter has no
> -		 * changes, (2) the filter has too many changes, or (3) it
> -		 * wasn't computed (eg., due to '--max-new-filters').
> -		 *
> -		 * If either (1) or (2) is the case, the 'large' bit will be set
> -		 * for this Bloom filter. If it is unset, then it wasn't
> -		 * computed. In that case, return nothing, since we don't have
> -		 * that filter in the graph.
> -		 */
> -		return 0;
> -	}
> -
>  	filter->len = end_index - start_index;
>  	filter->data = (unsigned char *)(g->chunk_bloom_data +
>  					sizeof(unsigned char) * start_index +
> @@ -212,16 +197,20 @@ struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
>
>  	if (!filter->data) {
>  		load_commit_graph_info(r, c);
> -		if (commit_graph_position(c) != COMMIT_NOT_FROM_GRAPH &&
> -			load_bloom_filter_from_graph(r->objects->commit_graph, filter, c))
> -				return filter;
> +		if (commit_graph_position(c) != COMMIT_NOT_FROM_GRAPH)
> +			load_bloom_filter_from_graph(r->objects->commit_graph, filter, c);
>  	}
>
> -	if (filter->data)
> +	if (filter && filter->len)
>  		return filter;
>  	if (!compute_if_not_present)
>  		return NULL;
>
> +	if (filter && !filter->len &&
> +	    get_bloom_filter_large_in_graph(r->objects->commit_graph, c,
> +	    				    settings->max_changed_paths))
> +		return filter;
> +
>  	repo_diff_setup(r, &diffopt);
>  	diffopt.flags.recursive = 1;
>  	diffopt.detect_rename = 0;
> diff --git a/commit-graph.c b/commit-graph.c
> index 4aae5471e3..ea89f431cc 100644
> --- a/commit-graph.c
> +++ b/commit-graph.c
> @@ -435,17 +435,9 @@ struct commit_graph *parse_commit_graph(struct repository *r,
>  			if (graph->chunk_bloom_large_filters)
>  				chunk_repeated = 1;
>  			else if (r->settings.commit_graph_read_changed_paths) {
> -				size_t alloc = get_be64(chunk_lookup + 4) - chunk_offset - sizeof(uint32_t);
> +				graph->bloom_large_alloc = get_be64(chunk_lookup + 4) - chunk_offset - sizeof(uint32_t);
>  				graph->chunk_bloom_large_filters = data + chunk_offset + sizeof(uint32_t);
>  				graph->bloom_filter_settings->max_changed_paths = get_be32(data + chunk_offset);
> -				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;
>  		}
> @@ -953,9 +945,9 @@ 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 max_changed_paths)
> +int get_bloom_filter_large_in_graph(struct commit_graph *g,
> +				    const struct commit *c,
> +				    uint32_t max_changed_paths)
>  {
>  	uint32_t graph_pos = commit_graph_position(c);
>  	if (graph_pos == COMMIT_NOT_FROM_GRAPH)
> @@ -964,8 +956,20 @@ static int get_bloom_filter_large_in_graph(struct commit_graph *g,
>  	while (g && graph_pos < g->num_commits_in_base)
>  		g = g->base_graph;
>
> -	if (!(g && g->bloom_large))
> +	if (!g || !g->bloom_large_alloc)
>  		return 0;
> +
> +	if (!g->bloom_large) {
> +		size_t j;
> +		g->bloom_large = bitmap_word_alloc(g->bloom_large_alloc);
> +
> +		for (j = 0; j < g->bloom_large->word_alloc; j++) {
> +			const void *data = g->chunk_bloom_large_filters +
> +					   j * sizeof(eword_t);
> +			g->bloom_large->words[j] = get_be64(data);
> +		}
> +	}
> +
>  	if (g->bloom_filter_settings->max_changed_paths != max_changed_paths) {
>  		/*
>  		 * Force all commits which are subject to a different
> diff --git a/commit-graph.h b/commit-graph.h
> index 75ef83708b..126fd43380 100644
> --- a/commit-graph.h
> +++ b/commit-graph.h
> @@ -51,6 +51,13 @@ void load_commit_graph_info(struct repository *r, struct commit *item);
>  struct tree *get_commit_tree_in_graph(struct repository *r,
>  				      const struct commit *c);
>
> +/*
> + * Returns 1 if this commit was marked in the BFXL chunk as having more
> + * than max_changed_paths changes.
> + */
> +int get_bloom_filter_large_in_graph(struct commit_graph *g,
> +				    const struct commit *c,
> +				    uint32_t max_changed_paths);
>  struct commit_graph {
>  	const unsigned char *data;
>  	size_t data_len;
> @@ -74,6 +81,7 @@ struct commit_graph {
>  	const unsigned char *chunk_bloom_data;
>  	const unsigned char *chunk_bloom_large_filters;
>
> +	size_t bloom_large_alloc;
>  	struct bitmap *bloom_large;
>
>  	struct bloom_filter_settings *bloom_filter_settings;
> --
> 2.28.0.38.gc6f546511c1
>
>

Thanks,
Taylor

  reply	other threads:[~2020-08-14 20:10 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
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 [this message]
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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