Re: [PATCH v2 10/21] read-cache: regenerate shared index if necessary

On Sat, Dec 17, 2016 at 03:55:36PM +0100, Christian Couder wrote:

+static const int default_max_percent_split_change = 20;
+
+static int too_many_not_shared_entries(struct index_state *istate)
+{
+	int i, not_shared = 0;
+	int max_split = git_config_get_max_percent_split_change();
+
+	switch (max_split) {
+	case -1:
+		/* not or badly configured: use the default value */
+		max_split = default_max_percent_split_change;
+		break;
+	case 0:
+		return 1; /* 0% means always write a new shared index */
+	case 100:
+		return 0; /* 100% means never write a new shared index */

I wonder if we really need to special case these here. If I read it
correctly, the expression at the end of this function will return 1
when max_split is 0, and 0 when max_split is 100 (not counting the
case when cache_nr is zero).

Perhaps it's good for documentation purpose. Though I find it hard to
see a use case for max_split == 0. Always creating a new shared index
sounds crazy.

+	default:
+		; /* do nothing: just use the configured value */
+	}
+
+	/* Count not shared entries */
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce = istate->cache[i];
+		if (!ce->index)
+			not_shared++;
+	}
+
+	return istate->cache_nr * max_split < not_shared * 100;
+}