pack-bitmap-write: fill bitmap with commit history

The current implementation of bitmap_writer_build() creates a
reachability bitmap for every walked commit. After computing a bitmap
for a commit, those bits are pushed to an in-progress bitmap for its
children.

fill_bitmap_commit() assumes the bits corresponding to objects
reachable from the parents of a commit are already set. This means that
when visiting a new commit, we only have to walk the objects reachable
between it and any of its parents.

A future change to bitmap_writer_build() will relax this condition so
not all parents have their bits set. Prepare for that by having
'fill_bitmap_commit()' walk parents until reaching commits whose bits
are already set. Then, walk the trees for these commits as well.

This has no functional change with the current implementation of
bitmap_writer_build().

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/pack-bitmap-write.c b/pack-bitmap-write.c
index 1eb9615df8aeb9e665055dda3ff94b9bf0901f29..957639241e25f311884db9e5f69c730aa1080c6c 100644 (file)
--- a/pack-bitmap-write.c
+++ b/pack-bitmap-write.c
@@ -12,6 +12,7 @@
 #include "sha1-lookup.h"
 #include "pack-objects.h"
 #include "commit-reach.h"
+#include "prio-queue.h"
 
 struct bitmapped_commit {
        struct commit *commit;
@@ -279,17 +280,30 @@ static void fill_bitmap_tree(struct bitmap *bitmap,
 }
 
 static void fill_bitmap_commit(struct bb_commit *ent,
-                              struct commit *commit)
+                              struct commit *commit,
+                              struct prio_queue *queue)
 {
        if (!ent->bitmap)
                ent->bitmap = bitmap_new();
 
-       /*
-        * mark ourselves, but do not bother with parents; their values
-        * will already have been propagated to us
-        */
        bitmap_set(ent->bitmap, find_object_pos(&commit->object.oid));
-       fill_bitmap_tree(ent->bitmap, get_commit_tree(commit));
+       prio_queue_put(queue, commit);
+
+       while (queue->nr) {
+               struct commit_list *p;
+               struct commit *c = prio_queue_get(queue);
+
+               bitmap_set(ent->bitmap, find_object_pos(&c->object.oid));
+               fill_bitmap_tree(ent->bitmap, get_commit_tree(c));
+
+               for (p = c->parents; p; p = p->next) {
+                       int pos = find_object_pos(&p->item->object.oid);
+                       if (!bitmap_get(ent->bitmap, pos)) {
+                               bitmap_set(ent->bitmap, pos);
+                               prio_queue_put(queue, p->item);
+                       }
+               }
+       }
 }
 
 static void store_selected(struct bb_commit *ent, struct commit *commit)
@@ -319,6 +333,7 @@ void bitmap_writer_build(struct packing_data *to_pack)
        struct bitmap_builder bb;
        size_t i;
        int nr_stored = 0; /* for progress */
+       struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
 
        writer.bitmaps = kh_init_oid_map();
        writer.to_pack = to_pack;
@@ -335,7 +350,7 @@ void bitmap_writer_build(struct packing_data *to_pack)
                struct commit *child;
                int reused = 0;
 
-               fill_bitmap_commit(ent, commit);
+               fill_bitmap_commit(ent, commit, &queue);
 
                if (ent->selected) {
                        store_selected(ent, commit);
@@ -360,6 +375,7 @@ void bitmap_writer_build(struct packing_data *to_pack)
                        bitmap_free(ent->bitmap);
                ent->bitmap = NULL;
        }
+       clear_prio_queue(&queue);
        bitmap_builder_clear(&bb);
 
        trace2_region_leave("pack-bitmap-write", "building_bitmaps_total",