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Merge branch 'jh/unpack-trees-micro-optim'

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In a 2- and 3-way merge of trees, more than one source trees often
end up sharing an identical subtree; optimize by not reading the
same tree multiple times in such a case.

* jh/unpack-trees-micro-optim:
  unpack-trees: avoid duplicate ODB lookups during checkout
This commit is contained in:
Junio C Hamano 2017-04-23 22:07:48 -07:00
commit 8868ba1962
1 changed files with 33 additions and 5 deletions
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38
unpack-trees.c
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@ -604,12 +604,18 @@ static int switch_cache_bottom(struct traverse_info *info)
return ret;
}
static inline int are_same_oid(struct name_entry *name_j, struct name_entry *name_k)
{
return name_j->oid && name_k->oid && !oidcmp(name_j->oid, name_k->oid);
}
static int traverse_trees_recursive(int n, unsigned long dirmask,
unsigned long df_conflicts,
struct name_entry *names,
struct traverse_info *info)
{
int i, ret, bottom;
int nr_buf = 0;
struct tree_desc t[MAX_UNPACK_TREES];
void *buf[MAX_UNPACK_TREES];
struct traverse_info newinfo;
@ -626,18 +632,40 @@ static int traverse_trees_recursive(int n, unsigned long dirmask,
newinfo.pathlen += tree_entry_len(p) + 1;
newinfo.df_conflicts |= df_conflicts;
/*
* Fetch the tree from the ODB for each peer directory in the
* n commits.
*
* For 2- and 3-way traversals, we try to avoid hitting the
* ODB twice for the same OID. This should yield a nice speed
* up in checkouts and merges when the commits are similar.
*
* We don't bother doing the full O(n^2) search for larger n,
* because wider traversals don't happen that often and we
* avoid the search setup.
*
* When 2 peer OIDs are the same, we just copy the tree
* descriptor data. This implicitly borrows the buffer
* data from the earlier cell.
*/
for (i = 0; i < n; i++, dirmask >>= 1) {
const unsigned char *sha1 = NULL;
if (dirmask & 1)
sha1 = names[i].oid->hash;
buf[i] = fill_tree_descriptor(t+i, sha1);
if (i > 0 && are_same_oid(&names[i], &names[i - 1]))
t[i] = t[i - 1];
else if (i > 1 && are_same_oid(&names[i], &names[i - 2]))
t[i] = t[i - 2];
else {
const unsigned char *sha1 = NULL;
if (dirmask & 1)
sha1 = names[i].oid->hash;
buf[nr_buf++] = fill_tree_descriptor(t+i, sha1);
}
}
bottom = switch_cache_bottom(&newinfo);
ret = traverse_trees(n, t, &newinfo);
restore_cache_bottom(&newinfo, bottom);
for (i = 0; i < n; i++)
for (i = 0; i < nr_buf; i++)
free(buf[i]);
return ret;