From 785bf2088e54ed8a450edb5c7371286ff6405605 Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 16 Jul 2021 05:22:31 +0000 Subject: [PATCH 1/7] merge-ort: resolve paths early when we have sufficient information When there are no directories involved at a given path, and all three sides have a file at that path, and two of the three sides of history match, we can immediately resolve the merge of that path in collect_merge_info() and do not need to wait until process_entries(). This is actually a very minor improvement: half the time when I run it, I see an improvement; the other half a slowdown. It seems to be in the range of noise. However, this idea serves as the beginning of some bigger optimizations coming in the following patches. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- merge-ort.c | 37 +++++++++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/merge-ort.c b/merge-ort.c index 8cfa0ccd3c8769..570432697366b9 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -1023,6 +1023,43 @@ static int collect_merge_info_callback(int n, return mask; } + /* + * If the sides match, and all three paths are present and are + * files, then we can take either as the resolution. We can't do + * this with trees, because there may be rename sources from the + * merge_base. + */ + if (sides_match && filemask == 0x07) { + /* use side1 (== side2) version as resolution */ + setup_path_info(opt, &pi, dirname, info->pathlen, fullpath, + names, names+1, side1_null, 0, + filemask, dirmask, 1); + return mask; + } + + /* + * If side1 matches mbase and all three paths are present and are + * files, then we can use side2 as the resolution. We cannot + * necessarily do so this for trees, because there may be rename + * destinations within side2. + */ + if (side1_matches_mbase && filemask == 0x07) { + /* use side2 version as resolution */ + setup_path_info(opt, &pi, dirname, info->pathlen, fullpath, + names, names+2, side2_null, 0, + filemask, dirmask, 1); + return mask; + } + + /* Similar to above but swapping sides 1 and 2 */ + if (side2_matches_mbase && filemask == 0x07) { + /* use side1 version as resolution */ + setup_path_info(opt, &pi, dirname, info->pathlen, fullpath, + names, names+1, side1_null, 0, + filemask, dirmask, 1); + return mask; + } + /* * Gather additional information used in rename detection. */ From 528fc51b6d899e080a877f9420efcca86c98b35e Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 16 Jul 2021 05:22:32 +0000 Subject: [PATCH 2/7] merge-ort: add some more explanations in collect_merge_info_callback() The previous patch possibly raises some questions about whether additional cases in collect_merge_info_callback() can be handled early. Add some explanations in the form of comments to help explain these better. While we're at it, add a few comments to denote what a few boolean '0' or '1' values stand for. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- merge-ort.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/merge-ort.c b/merge-ort.c index 570432697366b9..37aaac38b994d6 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -1018,8 +1018,8 @@ static int collect_merge_info_callback(int n, if (side1_matches_mbase && side2_matches_mbase) { /* mbase, side1, & side2 all match; use mbase as resolution */ setup_path_info(opt, &pi, dirname, info->pathlen, fullpath, - names, names+0, mbase_null, 0, - filemask, dirmask, 1); + names, names+0, mbase_null, 0 /* df_conflict */, + filemask, dirmask, 1 /* resolved */); return mask; } @@ -1061,14 +1061,24 @@ static int collect_merge_info_callback(int n, } /* - * Gather additional information used in rename detection. + * Sometimes we can tell that a source path need not be included in + * rename detection -- namely, whenever either + * side1_matches_mbase && side2_null + * or + * side2_matches_mbase && side1_null + * However, we call collect_rename_info() even in those cases, + * because exact renames are cheap and would let us remove both a + * source and destination path. We'll cull the unneeded sources + * later. */ collect_rename_info(opt, names, dirname, fullpath, filemask, dirmask, match_mask); /* - * Record information about the path so we can resolve later in - * process_entries. + * None of the special cases above matched, so we have a + * provisional conflict. (Rename detection might allow us to + * unconflict some more cases, but that comes later so all we can + * do now is record the different non-null file hashes.) */ setup_path_info(opt, &pi, dirname, info->pathlen, fullpath, names, NULL, 0, df_conflict, filemask, dirmask, 0); From d478f5675923d02d2676bf2e47f0ccdd4dba0da8 Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 16 Jul 2021 05:22:33 +0000 Subject: [PATCH 3/7] merge-ort: add data structures for allowable trivial directory resolves As noted a few commits ago, we can resolve individual files early if all three sides of the merge have a file at the path and two of the three sides match. We would really like to do the same thing with directories, because being able to do a trivial directory resolve means we don't have to recurse into the directory, potentially saving us a huge amount of time in both collect_merge_info() and process_entries(). Unfortunately, resolving directories early would mean missing any renames whose source or destination is underneath that directory. If we somehow knew there weren't any renames under the directory in question, then we could resolve it early. Sadly, it is impossible to determine whether there are renames under the directory in question without recursing into it, and this has traditionally kept us from ever implementing such an optimization. In commit f89b4f2bee ("merge-ort: skip rename detection entirely if possible", 2021-03-11), we added an additional reason that rename detection could be skipped entirely -- namely, if no *relevant* sources were present. Without completing collect_merge_info_callback(), we do not yet know if there are no relevant sources. However, we do know that if the current directory on one side matches the merge base, then every source file within that directory will not be RELEVANT_CONTENT, and a few simple checks can often let us rule out RELEVANT_LOCATION as well. This suggests we can just defer recursing into such directories until the end of collect_merge_info. Since the deferred directories are known to not add any relevant sources due to the above properties, then if there are no relevant sources after we've traversed all paths other than the deferred ones, then we know there are not any relevant sources. Under those conditions, rename detection is unnecessary, and that means we can resolve the deferred directories without recursing into them. Note that the logic for skipping rename detection was also modified further in commit 76e253793c ("merge-ort, diffcore-rename: employ cached renames when possible", 2021-01-30); in particular rename detection can be skipped if we already have cached renames for each relevant source. We can take advantage of this information as well with our deferral of recursing into directories where one side matches the merge base. Add some data structures that we will use to do these deferrals, with some lengthy comments explaining their purpose. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- merge-ort.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/merge-ort.c b/merge-ort.c index 37aaac38b994d6..15ce7f8c52be35 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -62,6 +62,53 @@ struct traversal_callback_data { struct name_entry names[3]; }; +struct deferred_traversal_data { + /* + * possible_trivial_merges: directories to be explored only when needed + * + * possible_trivial_merges is a map of directory names to + * dir_rename_mask. When we detect that a directory is unchanged on + * one side, we can sometimes resolve the directory without recursing + * into it. Renames are the only things that can prevent such an + * optimization. However, for rename sources: + * - If no parent directory needed directory rename detection, then + * no path under such a directory can be a relevant_source. + * and for rename destinations: + * - If no cached rename has a target path under the directory AND + * - If there are no unpaired relevant_sources elsewhere in the + * repository + * then we don't need any path under this directory for a rename + * destination. The only way to know the last item above is to defer + * handling such directories until the end of collect_merge_info(), + * in handle_deferred_entries(). + * + * For each we store dir_rename_mask, since that's the only bit of + * information we need, other than the path, to resume the recursive + * traversal. + */ + struct strintmap possible_trivial_merges; + + /* + * trivial_merges_okay: if trivial directory merges are okay + * + * See possible_trivial_merges above. The "no unpaired + * relevant_sources elsewhere in the repository" is a single boolean + * per merge side, which we store here. Note that while 0 means no, + * 1 only means "maybe" rather than "yes"; we optimistically set it + * to 1 initially and only clear when we determine it is unsafe to + * do trivial directory merges. + */ + unsigned trivial_merges_okay; + + /* + * target_dirs: ancestor directories of rename targets + * + * target_dirs contains all directory names that are an ancestor of + * any rename destination. + */ + struct strset target_dirs; +}; + struct rename_info { /* * All variables that are arrays of size 3 correspond to data tracked @@ -119,6 +166,8 @@ struct rename_info { */ struct strintmap relevant_sources[3]; + struct deferred_traversal_data deferred[3]; + /* * dir_rename_mask: * 0: optimization removing unmodified potential rename source okay @@ -501,6 +550,11 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti, strmap_clear(&renames->dir_rename_count[i], 1); } } + for (i = MERGE_SIDE1; i <= MERGE_SIDE2; ++i) { + strintmap_func(&renames->deferred[i].possible_trivial_merges); + strset_func(&renames->deferred[i].target_dirs); + renames->deferred[i].trivial_merges_okay = 1; /* 1 == maybe */ + } renames->cached_pairs_valid_side = 0; renames->dir_rename_mask = 0; @@ -4065,6 +4119,13 @@ static void merge_start(struct merge_options *opt, struct merge_result *result) strset_init_with_options(&renames->cached_target_names[i], NULL, 0); } + for (i = MERGE_SIDE1; i <= MERGE_SIDE2; i++) { + strintmap_init_with_options(&renames->deferred[i].possible_trivial_merges, + 0, NULL, 0); + strset_init_with_options(&renames->deferred[i].target_dirs, + NULL, 1); + renames->deferred[i].trivial_merges_okay = 1; /* 1 == maybe */ + } /* * Although we initialize opt->priv->paths with strdup_strings=0, From e0ef578eae4aea91920ef394a0d38170b39777d1 Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 16 Jul 2021 05:22:34 +0000 Subject: [PATCH 4/7] merge-ort: add a handle_deferred_entries() helper function In order to allow trivial directory resolution, we first need to be able to gather more information to determine if the optimization is safe. To enable that, we need a way of deferring the recursion into the directory until a later time. Naturally, deferring the entry into a subtree means that we need some function that will later recurse into the subdirectory exactly the same way that collect_merge_info_callback() would have done. Add a helper function that does this. For now this function is not used but a subsequent commit will change that. Future commits will also make the function sometimes resolve directories instead of traversing inside. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- merge-ort.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 64 insertions(+) diff --git a/merge-ort.c b/merge-ort.c index 15ce7f8c52be35..6f817958460078 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -1202,6 +1202,70 @@ static int collect_merge_info_callback(int n, return mask; } +MAYBE_UNUSED +static int handle_deferred_entries(struct merge_options *opt, + struct traverse_info *info) +{ + struct rename_info *renames = &opt->priv->renames; + struct hashmap_iter iter; + struct strmap_entry *entry; + int side, ret = 0; + + for (side = MERGE_SIDE1; side <= MERGE_SIDE2; side++) { + renames->deferred[side].trivial_merges_okay = 0; + strintmap_for_each_entry(&renames->deferred[side].possible_trivial_merges, + &iter, entry) { + const char *path = entry->key; + unsigned dir_rename_mask = (intptr_t)entry->value; + struct conflict_info *ci; + unsigned dirmask; + struct tree_desc t[3]; + void *buf[3] = {NULL,}; + int i; + + ci = strmap_get(&opt->priv->paths, path); + VERIFY_CI(ci); + dirmask = ci->dirmask; + + info->name = path; + info->namelen = strlen(path); + info->pathlen = info->namelen + 1; + + for (i = 0; i < 3; i++, dirmask >>= 1) { + if (i == 1 && ci->match_mask == 3) + t[1] = t[0]; + else if (i == 2 && ci->match_mask == 5) + t[2] = t[0]; + else if (i == 2 && ci->match_mask == 6) + t[2] = t[1]; + else { + const struct object_id *oid = NULL; + if (dirmask & 1) + oid = &ci->stages[i].oid; + buf[i] = fill_tree_descriptor(opt->repo, + t+i, oid); + } + } + + ci->match_mask &= ci->filemask; + opt->priv->current_dir_name = path; + renames->dir_rename_mask = dir_rename_mask; + if (renames->dir_rename_mask == 0 || + renames->dir_rename_mask == 0x07) + ret = traverse_trees(NULL, 3, t, info); + else + ret = traverse_trees_wrapper(NULL, 3, t, info); + + for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) + free(buf[i]); + + if (ret < 0) + return ret; + } + } + return ret; +} + static int collect_merge_info(struct merge_options *opt, struct tree *merge_base, struct tree *side1, From 5e1ca57a7bbf19ac6c92a4e032ca05345dc622bd Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 16 Jul 2021 05:22:35 +0000 Subject: [PATCH 5/7] merge-ort: defer recursing into directories when merge base is matched When one side of history matches the merge base (including when the merge base has no entry for the given directory), have collect_merge_info_callback() defer recursing into the directory. To ensure those entries are eventually handled, add a call to handled_deferred_entries() in collect_merge_info() after traverse_trees() returns. Note that the condition in collect_merge_info_callback() may look more complicated than necessary at first glance; renames->trivial_merges_okay[side] is always true until handle_deferred_entries() is called, and possible_trivial_merges[side] is always empty right now (and in the future won't be filled until handle_deferred_entries() is called). However, when handle_deferred_entries() calls traverse_trees() for the relevant deferred directories, those traverse_trees() calls will once again end up in collect_merge_info_callback() for all the entries under those subdirectories. The extra conditions are there for such deferred cases and will be used more as we do more with those variables. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- merge-ort.c | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) diff --git a/merge-ort.c b/merge-ort.c index 6f817958460078..7e624fcd366b0c 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -1147,8 +1147,36 @@ static int collect_merge_info_callback(int n, struct tree_desc t[3]; void *buf[3] = {NULL, NULL, NULL}; const char *original_dir_name; - int i, ret; + int i, ret, side; + /* + * Check for whether we can avoid recursing due to one side + * matching the merge base. The side that does NOT match is + * the one that might have a rename destination we need. + */ + assert(!side1_matches_mbase || !side2_matches_mbase); + side = side1_matches_mbase ? MERGE_SIDE2 : + side2_matches_mbase ? MERGE_SIDE1 : MERGE_BASE; + if (filemask == 0 && (dirmask == 2 || dirmask == 4)) { + /* + * Also defer recursing into new directories; set up a + * few variables to let us do so. + */ + ci->match_mask = (7 - dirmask); + side = dirmask / 2; + } + if (renames->dir_rename_mask != 0x07 && + side != MERGE_BASE && + renames->deferred[side].trivial_merges_okay && + !strset_contains(&renames->deferred[side].target_dirs, + pi.string)) { + strintmap_set(&renames->deferred[side].possible_trivial_merges, + pi.string, renames->dir_rename_mask); + renames->dir_rename_mask = prev_dir_rename_mask; + return mask; + } + + /* We need to recurse */ ci->match_mask &= filemask; newinfo = *info; newinfo.prev = info; @@ -1202,7 +1230,6 @@ static int collect_merge_info_callback(int n, return mask; } -MAYBE_UNUSED static int handle_deferred_entries(struct merge_options *opt, struct traverse_info *info) { @@ -1291,6 +1318,8 @@ static int collect_merge_info(struct merge_options *opt, trace2_region_enter("merge", "traverse_trees", opt->repo); ret = traverse_trees(NULL, 3, t, &info); + if (ret == 0) + ret = handle_deferred_entries(opt, &info); trace2_region_leave("merge", "traverse_trees", opt->repo); return ret; From 7bee6c100431e5c24cf27b5a7cfc9f67c8c66751 Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 16 Jul 2021 05:22:36 +0000 Subject: [PATCH 6/7] merge-ort: avoid recursing into directories when we don't need to MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This combines the work of the last several patches, and implements the conditions when we don't need to recurse into directories. It's perhaps easiest to see the logic by separating the fact that a directory might have both rename sources and rename destinations: * rename sources: only files present in the merge base can serve as rename sources, and only when one side deletes that file. When the tree on one side matches the merge base, that means every file within the subtree matches the merge base. This means that the skip-irrelevant-rename-detection optimization from before kicks in and we don't need any of these files as rename sources. * rename destinations: the tree that does not match the merge base might have newly added and hence unmatched destination files. This is what usually prevents us from doing trivial directory resolutions in the merge machinery. However, the fact that we have deferred recursing into this directory until the end means we know whether there are any unmatched relevant potential rename sources elsewhere in this merge. If there are no unmatched such relevant sources anywhere, then there is no need to look for unmatched potential rename destinations to match them with. This informs our algorithm: * Search through relevant_sources; if we have entries, they better all be reflected in cached_pairs or cached_irrelevant, otherwise they represent an unmatched potential rename source (causing the optimization to be disallowed). * For any relevant_source represented in cached_pairs, we do need to to make sure to get the destination for each source, meaning we need to recurse into any ancestor directories of those destinations. * Once we've recursed into all the rename destinations for any relevant_sources in cached_pairs, we can then do the trivial directory resolution for the remaining directories. For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows: Before After no-renames: 5.235 s ± 0.042 s 205.1 ms ± 3.8 ms mega-renames: 9.419 s ± 0.107 s 1.564 s ± 0.010 s just-one-mega: 480.1 ms ± 3.9 ms 479.5 ms ± 3.9 ms Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- merge-ort.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 99 insertions(+), 3 deletions(-) diff --git a/merge-ort.c b/merge-ort.c index 7e624fcd366b0c..ad94b30a76d640 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -1230,6 +1230,18 @@ static int collect_merge_info_callback(int n, return mask; } +static void resolve_trivial_directory_merge(struct conflict_info *ci, int side) +{ + VERIFY_CI(ci); + assert((side == 1 && ci->match_mask == 5) || + (side == 2 && ci->match_mask == 3)); + oidcpy(&ci->merged.result.oid, &ci->stages[side].oid); + ci->merged.result.mode = ci->stages[side].mode; + ci->merged.is_null = is_null_oid(&ci->stages[side].oid); + ci->match_mask = 0; + ci->merged.clean = 1; /* (ci->filemask == 0); */ +} + static int handle_deferred_entries(struct merge_options *opt, struct traverse_info *info) { @@ -1239,9 +1251,72 @@ static int handle_deferred_entries(struct merge_options *opt, int side, ret = 0; for (side = MERGE_SIDE1; side <= MERGE_SIDE2; side++) { - renames->deferred[side].trivial_merges_okay = 0; - strintmap_for_each_entry(&renames->deferred[side].possible_trivial_merges, - &iter, entry) { + unsigned optimization_okay = 1; + struct strintmap copy; + + /* Loop over the set of paths we need to know rename info for */ + strset_for_each_entry(&renames->relevant_sources[side], + &iter, entry) { + char *rename_target, *dir, *dir_marker; + struct strmap_entry *e; + + /* + * If we don't know delete/rename info for this path, + * then we need to recurse into all trees to get all + * adds to make sure we have it. + */ + if (strset_contains(&renames->cached_irrelevant[side], + entry->key)) + continue; + e = strmap_get_entry(&renames->cached_pairs[side], + entry->key); + if (!e) { + optimization_okay = 0; + break; + } + + /* If this is a delete, we have enough info already */ + rename_target = e->value; + if (!rename_target) + continue; + + /* If we already walked the rename target, we're good */ + if (strmap_contains(&opt->priv->paths, rename_target)) + continue; + + /* + * Otherwise, we need to get a list of directories that + * will need to be recursed into to get this + * rename_target. + */ + dir = xstrdup(rename_target); + while ((dir_marker = strrchr(dir, '/'))) { + *dir_marker = '\0'; + if (strset_contains(&renames->deferred[side].target_dirs, + dir)) + break; + strset_add(&renames->deferred[side].target_dirs, + dir); + } + free(dir); + } + renames->deferred[side].trivial_merges_okay = optimization_okay; + /* + * We need to recurse into any directories in + * possible_trivial_merges[side] found in target_dirs[side]. + * But when we recurse, we may need to queue up some of the + * subdirectories for possible_trivial_merges[side]. Since + * we can't safely iterate through a hashmap while also adding + * entries, move the entries into 'copy', iterate over 'copy', + * and then we'll also iterate anything added into + * possible_trivial_merges[side] once this loop is done. + */ + copy = renames->deferred[side].possible_trivial_merges; + strintmap_init_with_options(&renames->deferred[side].possible_trivial_merges, + 0, + NULL, + 0); + strintmap_for_each_entry(©, &iter, entry) { const char *path = entry->key; unsigned dir_rename_mask = (intptr_t)entry->value; struct conflict_info *ci; @@ -1254,6 +1329,13 @@ static int handle_deferred_entries(struct merge_options *opt, VERIFY_CI(ci); dirmask = ci->dirmask; + if (optimization_okay && + !strset_contains(&renames->deferred[side].target_dirs, + path)) { + resolve_trivial_directory_merge(ci, side); + continue; + } + info->name = path; info->namelen = strlen(path); info->pathlen = info->namelen + 1; @@ -1289,6 +1371,20 @@ static int handle_deferred_entries(struct merge_options *opt, if (ret < 0) return ret; } + strintmap_clear(©); + strintmap_for_each_entry(&renames->deferred[side].possible_trivial_merges, + &iter, entry) { + const char *path = entry->key; + struct conflict_info *ci; + + ci = strmap_get(&opt->priv->paths, path); + VERIFY_CI(ci); + + assert(renames->deferred[side].trivial_merges_okay && + !strset_contains(&renames->deferred[side].target_dirs, + path)); + resolve_trivial_directory_merge(ci, side); + } } return ret; } From 8b09a900a1f1f00d4deb04f567994ae8f1804b5e Mon Sep 17 00:00:00 2001 From: Elijah Newren Date: Fri, 16 Jul 2021 05:22:37 +0000 Subject: [PATCH 7/7] merge-ort: restart merge with cached renames to reduce process entry cost MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The merge algorithm mostly consists of the following three functions: collect_merge_info() detect_and_process_renames() process_entries() Prior to the trivial directory resolution optimization of the last half dozen commits, process_entries() was consistently the slowest, followed by collect_merge_info(), then detect_and_process_renames(). When the trivial directory resolution applies, it often dramatically decreases the amount of time spent in the two slower functions. Looking at the performance results in the previous commit, the trivial directory resolution optimization helps amazingly well when there are no relevant renames. It also helps really well when reapplying a long series of linear commits (such as in a rebase or cherry-pick), since the relevant renames may well be cached from the first reapplied commit. But when there are any relevant renames that are not cached (represented by the just-one-mega testcase), then the optimization does not help at all. Often, I noticed that when the optimization does not apply, it is because there are a handful of relevant sources -- maybe even only one. It felt frustrating to need to recurse into potentially hundreds or even thousands of directories just for a single rename, but it was needed for correctness. However, staring at this list of functions and noticing that process_entries() is the most expensive and knowing I could avoid it if I had cached renames suggested a simple idea: change collect_merge_info() detect_and_process_renames() process_entries() into collect_merge_info() detect_and_process_renames() collect_merge_info() detect_and_process_renames() process_entries() This may seem odd and look like more work. However, note that although we run collect_merge_info() twice, the second time we get to employ trivial directory resolves, which makes it much faster, so the increased time in collect_merge_info() is small. While we run detect_and_process_renames() again, all renames are cached so it's nearly a no-op (we don't call into diffcore_rename_extended() but we do have a little bit of data structure checking and fixing up). And the big payoff comes from the fact that process_entries(), will be much faster due to having far fewer entries to process. This restarting only makes sense if we can save recursing into enough directories to make it worth our while. Introduce a simple heuristic to guide this. Note that this heuristic uses a "wanted_factor" that I have virtually no actual real world data for, just some back-of-the-envelope quasi-scientific calculations that I included in some comments and then plucked a simple round number out of thin air. It could be that tweaking this number to make it either higher or lower improves the optimization. (There's slightly more here; when I first introduced this optimization, I used a factor of 10, because I was completely confident it was big enough to not cause slowdowns in special cases. I was certain it was higher than needed. Several months later, I added the rough calculations which make me think the optimal number is close to 2; but instead of pushing to the limit, I just bumped it to 3 to reduce the risk that there are special cases where this optimization can result in slowing down the code a little. If the ratio of path counts is below 3, we probably will only see minor performance improvements at best anyway.) Also, note that while the diffstat looks kind of long (nearly 100 lines), more than half of it is in two comments explaining how things work. For the testcases mentioned in commit 557ac0350d ("merge-ort: begin performance work; instrument with trace2_region_* calls", 2020-10-28), this change improves the performance as follows: Before After no-renames: 205.1 ms ± 3.8 ms 204.2 ms ± 3.0 ms mega-renames: 1.564 s ± 0.010 s 1.076 s ± 0.015 s just-one-mega: 479.5 ms ± 3.9 ms 364.1 ms ± 7.0 ms Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano --- merge-ort.c | 92 +++++++++++++++++++++++++++-- t/t6423-merge-rename-directories.sh | 2 +- 2 files changed, 87 insertions(+), 7 deletions(-) diff --git a/merge-ort.c b/merge-ort.c index ad94b30a76d640..e75b524153ecb5 100644 --- a/merge-ort.c +++ b/merge-ort.c @@ -213,6 +213,7 @@ struct rename_info { * MERGE_SIDE2: cached data from side2 can be reused * MERGE_SIDE1: cached data from side1 can be reused * 0: no cached data can be reused + * -1: See redo_after_renames; both sides can be reused. */ int cached_pairs_valid_side; @@ -258,6 +259,28 @@ struct rename_info { */ struct strset cached_irrelevant[3]; + /* + * redo_after_renames: optimization flag for "restarting" the merge + * + * Sometimes it pays to detect renames, cache them, and then + * restart the merge operation from the beginning. The reason for + * this is that when we know where all the renames are, we know + * whether a certain directory has any paths under it affected -- + * and if a directory is not affected then it permits us to do + * trivial tree merging in more cases. Doing trivial tree merging + * prevents the need to run process_entry() on every path + * underneath trees that can be trivially merged, and + * process_entry() is more expensive than collect_merge_info() -- + * plus, the second collect_merge_info() will be much faster since + * it doesn't have to recurse into the relevant trees. + * + * Values for this flag: + * 0 = don't bother, not worth it (or conditions not yet checked) + * 1 = conditions for optimization met, optimization worthwhile + * 2 = we already did it (don't restart merge yet again) + */ + unsigned redo_after_renames; + /* * needed_limit: value needed for inexact rename detection to run * @@ -541,7 +564,8 @@ static void clear_or_reinit_internal_opts(struct merge_options_internal *opti, strintmap_func(&renames->relevant_sources[i]); if (!reinitialize) assert(renames->cached_pairs_valid_side == 0); - if (i != renames->cached_pairs_valid_side) { + if (i != renames->cached_pairs_valid_side && + -1 != renames->cached_pairs_valid_side) { strset_func(&renames->cached_target_names[i]); strmap_func(&renames->cached_pairs[i], 1); strset_func(&renames->cached_irrelevant[i]); @@ -1249,7 +1273,9 @@ static int handle_deferred_entries(struct merge_options *opt, struct hashmap_iter iter; struct strmap_entry *entry; int side, ret = 0; + int path_count_before, path_count_after = 0; + path_count_before = strmap_get_size(&opt->priv->paths); for (side = MERGE_SIDE1; side <= MERGE_SIDE2; side++) { unsigned optimization_okay = 1; struct strintmap copy; @@ -1385,7 +1411,32 @@ static int handle_deferred_entries(struct merge_options *opt, path)); resolve_trivial_directory_merge(ci, side); } + if (!optimization_okay || path_count_after) + path_count_after = strmap_get_size(&opt->priv->paths); } + if (path_count_after) { + /* + * The choice of wanted_factor here does not affect + * correctness, only performance. When the + * path_count_after / path_count_before + * ratio is high, redoing after renames is a big + * performance boost. I suspect that redoing is a wash + * somewhere near a value of 2, and below that redoing will + * slow things down. I applied a fudge factor and picked + * 3; see the commit message when this was introduced for + * back of the envelope calculations for this ratio. + */ + const int wanted_factor = 3; + + /* We should only redo collect_merge_info one time */ + assert(renames->redo_after_renames == 0); + + if (path_count_after / path_count_before >= wanted_factor) { + renames->redo_after_renames = 1; + renames->cached_pairs_valid_side = -1; + } + } else if (renames->redo_after_renames == 2) + renames->redo_after_renames = 0; return ret; } @@ -2828,8 +2879,8 @@ static int compare_pairs(const void *a_, const void *b_) } /* Call diffcore_rename() to update deleted/added pairs into rename pairs */ -static void detect_regular_renames(struct merge_options *opt, - unsigned side_index) +static int detect_regular_renames(struct merge_options *opt, + unsigned side_index) { struct diff_options diff_opts; struct rename_info *renames = &opt->priv->renames; @@ -2842,7 +2893,7 @@ static void detect_regular_renames(struct merge_options *opt, * side had directory renames. */ resolve_diffpair_statuses(&renames->pairs[side_index]); - return; + return 0; } partial_clear_dir_rename_count(&renames->dir_rename_count[side_index]); @@ -2868,6 +2919,8 @@ static void detect_regular_renames(struct merge_options *opt, trace2_region_leave("diff", "diffcore_rename", opt->repo); resolve_diffpair_statuses(&diff_queued_diff); + if (diff_opts.needed_rename_limit > 0) + renames->redo_after_renames = 0; if (diff_opts.needed_rename_limit > renames->needed_limit) renames->needed_limit = diff_opts.needed_rename_limit; @@ -2877,6 +2930,8 @@ static void detect_regular_renames(struct merge_options *opt, diff_queued_diff.nr = 0; diff_queued_diff.queue = NULL; diff_flush(&diff_opts); + + return 1; } /* @@ -2966,14 +3021,32 @@ static int detect_and_process_renames(struct merge_options *opt, struct diff_queue_struct combined; struct rename_info *renames = &opt->priv->renames; int need_dir_renames, s, clean = 1; + unsigned detection_run = 0; memset(&combined, 0, sizeof(combined)); if (!possible_renames(renames)) goto cleanup; trace2_region_enter("merge", "regular renames", opt->repo); - detect_regular_renames(opt, MERGE_SIDE1); - detect_regular_renames(opt, MERGE_SIDE2); + detection_run |= detect_regular_renames(opt, MERGE_SIDE1); + detection_run |= detect_regular_renames(opt, MERGE_SIDE2); + if (renames->redo_after_renames && detection_run) { + int i, side; + struct diff_filepair *p; + + /* Cache the renames, we found */ + for (side = MERGE_SIDE1; side <= MERGE_SIDE2; side++) { + for (i = 0; i < renames->pairs[side].nr; ++i) { + p = renames->pairs[side].queue[i]; + possibly_cache_new_pair(renames, p, side, NULL); + } + } + + /* Restart the merge with the cached renames */ + renames->redo_after_renames = 2; + trace2_region_leave("merge", "regular renames", opt->repo); + goto cleanup; + } use_cached_pairs(opt, &renames->cached_pairs[1], &renames->pairs[1]); use_cached_pairs(opt, &renames->cached_pairs[2], &renames->pairs[2]); trace2_region_leave("merge", "regular renames", opt->repo); @@ -4403,6 +4476,7 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt, opt->subtree_shift); } +redo: trace2_region_enter("merge", "collect_merge_info", opt->repo); if (collect_merge_info(opt, merge_base, side1, side2) != 0) { /* @@ -4422,6 +4496,12 @@ static void merge_ort_nonrecursive_internal(struct merge_options *opt, result->clean = detect_and_process_renames(opt, merge_base, side1, side2); trace2_region_leave("merge", "renames", opt->repo); + if (opt->priv->renames.redo_after_renames == 2) { + trace2_region_enter("merge", "reset_maps", opt->repo); + clear_or_reinit_internal_opts(opt->priv, 1); + trace2_region_leave("merge", "reset_maps", opt->repo); + goto redo; + } trace2_region_enter("merge", "process_entries", opt->repo); process_entries(opt, &working_tree_oid); diff --git a/t/t6423-merge-rename-directories.sh b/t/t6423-merge-rename-directories.sh index 4af4fb00386efe..5b81a130e9c450 100755 --- a/t/t6423-merge-rename-directories.sh +++ b/t/t6423-merge-rename-directories.sh @@ -4797,7 +4797,7 @@ test_setup_12f () { ) } -test_expect_merge_algorithm failure failure '12f: Trivial directory resolve, caching, all kinds of fun' ' +test_expect_merge_algorithm failure success '12f: Trivial directory resolve, caching, all kinds of fun' ' test_setup_12f && ( cd 12f &&