Ecache: Should know its arena_ind.

What we call an arena_ind is really the index associated with some particular
set of ehooks; the arena is just the user-visible portion of that.  Making this
explicit, and reframing checks in terms of that, makes the code simpler and
cleaner, and helps us avoid passing the arena itself all throughout extent code.

This lets us put back an arena-specific assert.

src/arena.c

@@ -2018,14 +2018,16 @@ arena_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks) {
 	 * are likely to be reused soon after deallocation, and the cost of
 	 * merging/splitting extents is non-trivial.
 	 */
-	if (ecache_init(tsdn, &arena->ecache_dirty, extent_state_dirty, true)) {
+	if (ecache_init(tsdn, &arena->ecache_dirty, extent_state_dirty, ind,
+	    true)) {
 		goto label_error;
 	}
 	/*
 	 * Coalesce muzzy extents immediately, because operations on them are in
 	 * the critical path much less often than for dirty extents.
 	 */
-	if (ecache_init(tsdn, &arena->ecache_muzzy, extent_state_muzzy, false)) {
+	if (ecache_init(tsdn, &arena->ecache_muzzy, extent_state_muzzy, ind,
+	    false)) {
 		goto label_error;
 	}
 	/*
@@ -2035,7 +2037,7 @@ arena_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks) {
 	 * in the critical path.
 	 */
 	if (ecache_init(tsdn, &arena->ecache_retained, extent_state_retained,
-	    false)) {
+	    ind, false)) {
 		goto label_error;
 	}
 

src/ecache.c

@@ -2,13 +2,14 @@
 #include "jemalloc/internal/jemalloc_internal_includes.h"
 
 bool
-ecache_init(tsdn_t *tsdn, ecache_t *ecache, extent_state_t state,
+ecache_init(tsdn_t *tsdn, ecache_t *ecache, extent_state_t state, unsigned ind,
     bool delay_coalesce) {
 	if (malloc_mutex_init(&ecache->mtx, "extents", WITNESS_RANK_EXTENTS,
 	    malloc_mutex_rank_exclusive)) {
 		return true;
 	}
 	ecache->state = state;
+	ecache->ind = ind;
 	ecache->delay_coalesce = delay_coalesce;
 	eset_init(&ecache->eset, state);
 	return false;

src/extent2.c

@@ -1062,6 +1062,8 @@ extent_alloc_wrapper(tsdn_t *tsdn, arena_t *arena, ehooks_t *ehooks,
 static bool
 extent_can_coalesce(ecache_t *ecache, const edata_t *inner,
     const edata_t *outer) {
+	assert(edata_arena_ind_get(inner) == ecache_ind_get(ecache));
+
 	if (edata_arena_ind_get(inner) != edata_arena_ind_get(outer)) {
 		return false;
 	}