mirror of
https://github.com/git/git.git
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Johannes Schindelin
e4621a0169
Since589127caa7(packfile: move list of packs into the packfile store, 2025-10-30), there is a performance regression when many packfiles need to be loaded: `packfile_store_add_pack()` now calls `packfile_list_remove_internal()` to detect whether the packfile was _already_ in the list, and if so, move it to the end of the list. This function linearly scans the existing list before every insertion. Newly loading N packs therefore has complexity O(N²). In one reported use case (https://github.com/microsoft/git/issues/970), N equals 37,815 and caused a slow-down of a simple `git rev-parse --short HEAD` (which is regularly executed as part of `GIT_PS1`) from 0.4s to 4.5s. Let's fix this by establishing a fast path for known-new packfiles. The keen reader will note that there is currently only a single, "known-new" caller of the `packfile_list_append()` function, and wonder why not simply remove this check whether the packfile already exists in the list? Originally, when above-mentioned commit introduced that logic, there was a second caller in `prepare_midx()`, which would have required that check, but that caller was removed in6aff1f25a0(packfile: always add packfiles to MRU when adding a pack, 2025-10-30). Still, the function is declared in a header file, and to avoid any problems with in-flight or downstream callers, it is safer to extend the signature to be explicit whether or not to skip that check. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
88 lines
1.8 KiB
C
88 lines
1.8 KiB
C
#include "git-compat-util.h"
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#include "packfile.h"
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#include "packfile-list.h"
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void packfile_list_clear(struct packfile_list *list)
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{
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struct packfile_list_entry *e, *next;
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for (e = list->head; e; e = next) {
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next = e->next;
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free(e);
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}
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list->head = list->tail = NULL;
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}
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static struct packfile_list_entry *packfile_list_remove_internal(struct packfile_list *list,
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struct packed_git *pack)
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{
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struct packfile_list_entry *e, *prev;
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for (e = list->head, prev = NULL; e; prev = e, e = e->next) {
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if (e->pack != pack)
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continue;
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if (prev)
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prev->next = e->next;
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if (list->head == e)
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list->head = e->next;
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if (list->tail == e)
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list->tail = prev;
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return e;
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}
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return NULL;
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}
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void packfile_list_remove(struct packfile_list *list, struct packed_git *pack)
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{
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free(packfile_list_remove_internal(list, pack));
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}
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void packfile_list_prepend(struct packfile_list *list, struct packed_git *pack)
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{
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struct packfile_list_entry *entry;
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entry = packfile_list_remove_internal(list, pack);
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if (!entry) {
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entry = xmalloc(sizeof(*entry));
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entry->pack = pack;
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}
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entry->next = list->head;
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list->head = entry;
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if (!list->tail)
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list->tail = entry;
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}
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void packfile_list_append(struct packfile_list *list, struct packed_git *pack,
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int skip_dup_check)
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{
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struct packfile_list_entry *entry;
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entry = skip_dup_check ? NULL : packfile_list_remove_internal(list, pack);
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if (!entry) {
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entry = xmalloc(sizeof(*entry));
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entry->pack = pack;
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}
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entry->next = NULL;
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if (list->tail) {
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list->tail->next = entry;
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list->tail = entry;
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} else {
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list->head = list->tail = entry;
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}
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}
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struct packed_git *packfile_list_find_oid(struct packfile_list_entry *packs,
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const struct object_id *oid)
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{
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for (; packs; packs = packs->next)
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if (find_pack_entry_one(oid, packs->pack))
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return packs->pack;
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return NULL;
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}
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