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After we are done using Bloom filters, we do not currently clean up any memory allocated by the commit slab used to store those filters in the first place. Besides the bloom_filter structures themselves, there is mostly nothing to free() in the first place, since in the read-only path all Bloom filter's `data` members point to a memory mapped region in the commit-graph file itself. But when generating Bloom filters from scratch (or initializing truncated filters) we allocate additional memory to store the filter's data. Keep track of when we need to free() this additional chunk of memory by using an extra pointer `to_free`. Most of the time this will be NULL (indicating that we are representing an existing Bloom filter stored in a memory mapped region). When it is non-NULL, free it before discarding the Bloom filters slab. Suggested-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Taylor Blau <me@ttaylorr.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
140 lines
4 KiB
C
140 lines
4 KiB
C
#ifndef BLOOM_H
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#define BLOOM_H
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struct commit;
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struct repository;
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struct commit_graph;
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struct bloom_filter_settings {
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/*
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* The version of the hashing technique being used.
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* The newest version is 2, which is
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* the seeded murmur3 hashing technique implemented
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* in bloom.c. Bloom filters of version 1 were created
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* with prior versions of Git, which had a bug in the
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* implementation of the hash function.
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*/
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uint32_t hash_version;
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/*
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* The number of times a path is hashed, i.e. the
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* number of bit positions tht cumulatively
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* determine whether a path is present in the
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* Bloom filter.
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*/
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uint32_t num_hashes;
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/*
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* The minimum number of bits per entry in the Bloom
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* filter. If the filter contains 'n' entries, then
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* filter size is the minimum number of 8-bit words
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* that contain n*b bits.
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*/
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uint32_t bits_per_entry;
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/*
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* The maximum number of changed paths per commit
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* before declaring a Bloom filter to be too-large.
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*
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* Not written to the commit-graph file.
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*/
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uint32_t max_changed_paths;
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};
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#define DEFAULT_BLOOM_MAX_CHANGES 512
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#define DEFAULT_BLOOM_FILTER_SETTINGS { 1, 7, 10, DEFAULT_BLOOM_MAX_CHANGES }
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#define BITS_PER_WORD 8
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#define BLOOMDATA_CHUNK_HEADER_SIZE 3 * sizeof(uint32_t)
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/*
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* A bloom_filter struct represents a data segment to
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* use when testing hash values. The 'len' member
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* dictates how many entries are stored in
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* 'data'.
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*/
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struct bloom_filter {
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unsigned char *data;
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size_t len;
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int version;
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void *to_free;
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};
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/*
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* A bloom_key represents the k hash values for a
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* given string. These can be precomputed and
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* stored in a bloom_key for re-use when testing
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* against a bloom_filter. The number of hashes is
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* given by the Bloom filter settings and is the same
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* for all Bloom filters and keys interacting with
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* the loaded version of the commit graph file and
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* the Bloom data chunks.
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*/
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struct bloom_key {
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uint32_t *hashes;
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};
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int load_bloom_filter_from_graph(struct commit_graph *g,
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struct bloom_filter *filter,
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uint32_t graph_pos);
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/*
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* Calculate the murmur3 32-bit hash value for the given data
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* using the given seed.
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* Produces a uniformly distributed hash value.
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* Not considered to be cryptographically secure.
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* Implemented as described in https://en.wikipedia.org/wiki/MurmurHash#Algorithm
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*/
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uint32_t murmur3_seeded_v2(uint32_t seed, const char *data, size_t len);
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void fill_bloom_key(const char *data,
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size_t len,
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struct bloom_key *key,
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const struct bloom_filter_settings *settings);
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void clear_bloom_key(struct bloom_key *key);
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void add_key_to_filter(const struct bloom_key *key,
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struct bloom_filter *filter,
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const struct bloom_filter_settings *settings);
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void init_bloom_filters(void);
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void deinit_bloom_filters(void);
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enum bloom_filter_computed {
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BLOOM_NOT_COMPUTED = (1 << 0),
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BLOOM_COMPUTED = (1 << 1),
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BLOOM_TRUNC_LARGE = (1 << 2),
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BLOOM_TRUNC_EMPTY = (1 << 3),
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BLOOM_UPGRADED = (1 << 4),
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};
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struct bloom_filter *get_or_compute_bloom_filter(struct repository *r,
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struct commit *c,
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int compute_if_not_present,
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const struct bloom_filter_settings *settings,
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enum bloom_filter_computed *computed);
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/*
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* Find the Bloom filter associated with the given commit "c".
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*
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* If any of the following are true
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*
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* - the repository does not have a commit-graph, or
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* - the repository disables reading from the commit-graph, or
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* - the given commit does not have a Bloom filter computed, or
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* - there is a Bloom filter for commit "c", but it cannot be read
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* because the filter uses an incompatible version of murmur3
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*
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* , then `get_bloom_filter()` will return NULL. Otherwise, the corresponding
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* Bloom filter will be returned.
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*
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* For callers who wish to inspect Bloom filters with incompatible hash
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* versions, use get_or_compute_bloom_filter().
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*/
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struct bloom_filter *get_bloom_filter(struct repository *r, struct commit *c);
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int bloom_filter_contains(const struct bloom_filter *filter,
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const struct bloom_key *key,
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const struct bloom_filter_settings *settings);
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#endif
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