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![Jameson Miller](/assets/img/avatar_default.png)
It has been observed that the time spent loading an index with a large number of entries is partly dominated by malloc() calls. This change is in preparation for using memory pools to reduce the number of malloc() calls made to allocate cahce entries when loading an index. Add an API to allocate and discard cache entries, abstracting the details of managing the memory backing the cache entries. This commit does actually change how memory is managed - this will be done in a later commit in the series. This change makes the distinction between cache entries that are associated with an index and cache entries that are not associated with an index. A main use of cache entries is with an index, and we can optimize the memory management around this. We still have other cases where a cache entry is not persisted with an index, and so we need to handle the "transient" use case as well. To keep the congnitive overhead of managing the cache entries, there will only be a single discard function. This means there must be enough information kept with the cache entry so that we know how to discard them. A summary of the main functions in the API is: make_cache_entry: create cache entry for use in an index. Uses specified parameters to populate cache_entry fields. make_empty_cache_entry: Create an empty cache entry for use in an index. Returns cache entry with empty fields. make_transient_cache_entry: create cache entry that is not used in an index. Uses specified parameters to populate cache_entry fields. make_empty_transient_cache_entry: create cache entry that is not used in an index. Returns cache entry with empty fields. discard_cache_entry: A single function that knows how to discard a cache entry regardless of how it was allocated. Signed-off-by: Jameson Miller <jamill@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
343 lines
9.8 KiB
C
343 lines
9.8 KiB
C
#include "cache.h"
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#include "split-index.h"
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#include "ewah/ewok.h"
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struct split_index *init_split_index(struct index_state *istate)
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{
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if (!istate->split_index) {
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istate->split_index = xcalloc(1, sizeof(*istate->split_index));
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istate->split_index->refcount = 1;
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}
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return istate->split_index;
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}
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int read_link_extension(struct index_state *istate,
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const void *data_, unsigned long sz)
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{
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const unsigned char *data = data_;
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struct split_index *si;
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int ret;
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if (sz < the_hash_algo->rawsz)
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return error("corrupt link extension (too short)");
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si = init_split_index(istate);
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hashcpy(si->base_oid.hash, data);
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data += the_hash_algo->rawsz;
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sz -= the_hash_algo->rawsz;
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if (!sz)
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return 0;
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si->delete_bitmap = ewah_new();
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ret = ewah_read_mmap(si->delete_bitmap, data, sz);
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if (ret < 0)
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return error("corrupt delete bitmap in link extension");
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data += ret;
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sz -= ret;
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si->replace_bitmap = ewah_new();
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ret = ewah_read_mmap(si->replace_bitmap, data, sz);
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if (ret < 0)
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return error("corrupt replace bitmap in link extension");
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if (ret != sz)
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return error("garbage at the end of link extension");
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return 0;
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}
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int write_link_extension(struct strbuf *sb,
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struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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strbuf_add(sb, si->base_oid.hash, the_hash_algo->rawsz);
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if (!si->delete_bitmap && !si->replace_bitmap)
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return 0;
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ewah_serialize_strbuf(si->delete_bitmap, sb);
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ewah_serialize_strbuf(si->replace_bitmap, sb);
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return 0;
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}
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static void mark_base_index_entries(struct index_state *base)
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{
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int i;
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/*
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* To keep track of the shared entries between
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* istate->base->cache[] and istate->cache[], base entry
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* position is stored in each base entry. All positions start
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* from 1 instead of 0, which is reserved to say "this is a new
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* entry".
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*/
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for (i = 0; i < base->cache_nr; i++)
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base->cache[i]->index = i + 1;
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}
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void move_cache_to_base_index(struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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int i;
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/*
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* do not delete old si->base, its index entries may be shared
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* with istate->cache[]. Accept a bit of leaking here because
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* this code is only used by short-lived update-index.
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*/
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si->base = xcalloc(1, sizeof(*si->base));
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si->base->version = istate->version;
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/* zero timestamp disables racy test in ce_write_index() */
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si->base->timestamp = istate->timestamp;
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ALLOC_GROW(si->base->cache, istate->cache_nr, si->base->cache_alloc);
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si->base->cache_nr = istate->cache_nr;
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COPY_ARRAY(si->base->cache, istate->cache, istate->cache_nr);
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mark_base_index_entries(si->base);
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for (i = 0; i < si->base->cache_nr; i++)
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si->base->cache[i]->ce_flags &= ~CE_UPDATE_IN_BASE;
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}
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static void mark_entry_for_delete(size_t pos, void *data)
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{
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struct index_state *istate = data;
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if (pos >= istate->cache_nr)
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die("position for delete %d exceeds base index size %d",
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(int)pos, istate->cache_nr);
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istate->cache[pos]->ce_flags |= CE_REMOVE;
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istate->split_index->nr_deletions = 1;
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}
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static void replace_entry(size_t pos, void *data)
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{
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struct index_state *istate = data;
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struct split_index *si = istate->split_index;
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struct cache_entry *dst, *src;
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if (pos >= istate->cache_nr)
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die("position for replacement %d exceeds base index size %d",
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(int)pos, istate->cache_nr);
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if (si->nr_replacements >= si->saved_cache_nr)
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die("too many replacements (%d vs %d)",
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si->nr_replacements, si->saved_cache_nr);
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dst = istate->cache[pos];
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if (dst->ce_flags & CE_REMOVE)
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die("entry %d is marked as both replaced and deleted",
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(int)pos);
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src = si->saved_cache[si->nr_replacements];
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if (ce_namelen(src))
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die("corrupt link extension, entry %d should have "
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"zero length name", (int)pos);
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src->index = pos + 1;
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src->ce_flags |= CE_UPDATE_IN_BASE;
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src->ce_namelen = dst->ce_namelen;
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copy_cache_entry(dst, src);
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discard_cache_entry(src);
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si->nr_replacements++;
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}
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void merge_base_index(struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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unsigned int i;
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mark_base_index_entries(si->base);
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si->saved_cache = istate->cache;
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si->saved_cache_nr = istate->cache_nr;
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istate->cache_nr = si->base->cache_nr;
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istate->cache = NULL;
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istate->cache_alloc = 0;
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ALLOC_GROW(istate->cache, istate->cache_nr, istate->cache_alloc);
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COPY_ARRAY(istate->cache, si->base->cache, istate->cache_nr);
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si->nr_deletions = 0;
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si->nr_replacements = 0;
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ewah_each_bit(si->replace_bitmap, replace_entry, istate);
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ewah_each_bit(si->delete_bitmap, mark_entry_for_delete, istate);
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if (si->nr_deletions)
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remove_marked_cache_entries(istate);
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for (i = si->nr_replacements; i < si->saved_cache_nr; i++) {
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if (!ce_namelen(si->saved_cache[i]))
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die("corrupt link extension, entry %d should "
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"have non-zero length name", i);
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add_index_entry(istate, si->saved_cache[i],
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ADD_CACHE_OK_TO_ADD |
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ADD_CACHE_KEEP_CACHE_TREE |
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/*
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* we may have to replay what
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* merge-recursive.c:update_stages()
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* does, which has this flag on
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*/
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ADD_CACHE_SKIP_DFCHECK);
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si->saved_cache[i] = NULL;
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}
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ewah_free(si->delete_bitmap);
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ewah_free(si->replace_bitmap);
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FREE_AND_NULL(si->saved_cache);
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si->delete_bitmap = NULL;
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si->replace_bitmap = NULL;
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si->saved_cache_nr = 0;
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}
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void prepare_to_write_split_index(struct index_state *istate)
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{
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struct split_index *si = init_split_index(istate);
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struct cache_entry **entries = NULL, *ce;
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int i, nr_entries = 0, nr_alloc = 0;
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si->delete_bitmap = ewah_new();
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si->replace_bitmap = ewah_new();
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if (si->base) {
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/* Go through istate->cache[] and mark CE_MATCHED to
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* entry with positive index. We'll go through
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* base->cache[] later to delete all entries in base
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* that are not marked with either CE_MATCHED or
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* CE_UPDATE_IN_BASE. If istate->cache[i] is a
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* duplicate, deduplicate it.
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*/
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for (i = 0; i < istate->cache_nr; i++) {
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struct cache_entry *base;
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/* namelen is checked separately */
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const unsigned int ondisk_flags =
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CE_STAGEMASK | CE_VALID | CE_EXTENDED_FLAGS;
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unsigned int ce_flags, base_flags, ret;
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ce = istate->cache[i];
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if (!ce->index)
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continue;
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if (ce->index > si->base->cache_nr) {
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ce->index = 0;
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continue;
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}
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ce->ce_flags |= CE_MATCHED; /* or "shared" */
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base = si->base->cache[ce->index - 1];
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if (ce == base)
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continue;
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if (ce->ce_namelen != base->ce_namelen ||
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strcmp(ce->name, base->name)) {
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ce->index = 0;
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continue;
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}
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ce_flags = ce->ce_flags;
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base_flags = base->ce_flags;
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/* only on-disk flags matter */
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ce->ce_flags &= ondisk_flags;
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base->ce_flags &= ondisk_flags;
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ret = memcmp(&ce->ce_stat_data, &base->ce_stat_data,
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offsetof(struct cache_entry, name) -
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offsetof(struct cache_entry, ce_stat_data));
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ce->ce_flags = ce_flags;
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base->ce_flags = base_flags;
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if (ret)
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ce->ce_flags |= CE_UPDATE_IN_BASE;
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discard_cache_entry(base);
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si->base->cache[ce->index - 1] = ce;
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}
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for (i = 0; i < si->base->cache_nr; i++) {
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ce = si->base->cache[i];
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if ((ce->ce_flags & CE_REMOVE) ||
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!(ce->ce_flags & CE_MATCHED))
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ewah_set(si->delete_bitmap, i);
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else if (ce->ce_flags & CE_UPDATE_IN_BASE) {
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ewah_set(si->replace_bitmap, i);
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ce->ce_flags |= CE_STRIP_NAME;
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ALLOC_GROW(entries, nr_entries+1, nr_alloc);
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entries[nr_entries++] = ce;
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}
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if (is_null_oid(&ce->oid))
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istate->drop_cache_tree = 1;
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}
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}
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for (i = 0; i < istate->cache_nr; i++) {
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ce = istate->cache[i];
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if ((!si->base || !ce->index) && !(ce->ce_flags & CE_REMOVE)) {
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assert(!(ce->ce_flags & CE_STRIP_NAME));
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ALLOC_GROW(entries, nr_entries+1, nr_alloc);
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entries[nr_entries++] = ce;
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}
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ce->ce_flags &= ~CE_MATCHED;
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}
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/*
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* take cache[] out temporarily, put entries[] in its place
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* for writing
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*/
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si->saved_cache = istate->cache;
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si->saved_cache_nr = istate->cache_nr;
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istate->cache = entries;
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istate->cache_nr = nr_entries;
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}
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void finish_writing_split_index(struct index_state *istate)
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{
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struct split_index *si = init_split_index(istate);
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ewah_free(si->delete_bitmap);
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ewah_free(si->replace_bitmap);
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si->delete_bitmap = NULL;
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si->replace_bitmap = NULL;
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free(istate->cache);
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istate->cache = si->saved_cache;
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istate->cache_nr = si->saved_cache_nr;
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}
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void discard_split_index(struct index_state *istate)
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{
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struct split_index *si = istate->split_index;
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if (!si)
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return;
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istate->split_index = NULL;
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si->refcount--;
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if (si->refcount)
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return;
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if (si->base) {
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discard_index(si->base);
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free(si->base);
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}
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free(si);
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}
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void save_or_free_index_entry(struct index_state *istate, struct cache_entry *ce)
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{
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if (ce->index &&
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istate->split_index &&
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istate->split_index->base &&
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ce->index <= istate->split_index->base->cache_nr &&
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ce == istate->split_index->base->cache[ce->index - 1])
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ce->ce_flags |= CE_REMOVE;
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else
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discard_cache_entry(ce);
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}
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void replace_index_entry_in_base(struct index_state *istate,
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struct cache_entry *old_entry,
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struct cache_entry *new_entry)
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{
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if (old_entry->index &&
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istate->split_index &&
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istate->split_index->base &&
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old_entry->index <= istate->split_index->base->cache_nr) {
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new_entry->index = old_entry->index;
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if (old_entry != istate->split_index->base->cache[new_entry->index - 1])
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discard_cache_entry(istate->split_index->base->cache[new_entry->index - 1]);
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istate->split_index->base->cache[new_entry->index - 1] = new_entry;
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}
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}
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void add_split_index(struct index_state *istate)
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{
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if (!istate->split_index) {
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init_split_index(istate);
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istate->cache_changed |= SPLIT_INDEX_ORDERED;
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}
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}
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void remove_split_index(struct index_state *istate)
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{
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if (istate->split_index) {
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/*
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* can't discard_split_index(&the_index); because that
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* will destroy split_index->base->cache[], which may
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* be shared with the_index.cache[]. So yeah we're
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* leaking a bit here.
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*/
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istate->split_index = NULL;
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istate->cache_changed |= SOMETHING_CHANGED;
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}
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}
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