diff --git a/include/jemalloc/internal/pa.h b/include/jemalloc/internal/pa.h
index e1821e69..0df2b4b3 100644
--- a/include/jemalloc/internal/pa.h
+++ b/include/jemalloc/internal/pa.h
@@ -119,7 +119,10 @@ bool pa_shard_init(tsdn_t *tsdn, pa_shard_t *shard, base_t *base, unsigned ind,
     pa_shard_stats_t *stats, malloc_mutex_t *stats_mtx);
 size_t pa_shard_extent_sn_next(pa_shard_t *shard);
 
-edata_t *
-pa_alloc(tsdn_t *tsdn, pa_shard_t *shard, size_t size, size_t alignment,
-    bool slab, szind_t szind, bool *zero, size_t *mapped_add);
+edata_t *pa_alloc(tsdn_t *tsdn, pa_shard_t *shard, size_t size,
+    size_t alignment, bool slab, szind_t szind, bool *zero, size_t *mapped_add);
+/* Returns true on error, in which case nothing changed. */
+bool pa_expand(tsdn_t *tsdn, pa_shard_t *shard, edata_t *edata,
+    size_t new_usize, bool *zero, size_t *mapped_add);
+
 #endif /* JEMALLOC_INTERNAL_PA_H */
diff --git a/src/large.c b/src/large.c
index 26a1740c..ff43a8d1 100644
--- a/src/large.c
+++ b/src/large.c
@@ -101,57 +101,28 @@ static bool
 large_ralloc_no_move_expand(tsdn_t *tsdn, edata_t *edata, size_t usize,
     bool zero) {
 	arena_t *arena = arena_get_from_edata(edata);
-	size_t oldusize = edata_usize_get(edata);
-	ehooks_t *ehooks = arena_get_ehooks(arena);
-	size_t trailsize = usize - oldusize;
-
-	if (ehooks_merge_will_fail(ehooks)) {
-		return true;
-	}
 
 	if (config_fill && unlikely(opt_zero)) {
 		zero = true;
 	}
+
+	size_t old_usize = edata_usize_get(edata);
+
 	/*
 	 * Copy zero into is_zeroed_trail and pass the copy when allocating the
 	 * extent, so that it is possible to make correct zero fill decisions
 	 * below, even if is_zeroed_trail ends up true when zero is false.
 	 */
 	bool is_zeroed_trail = zero;
-	edata_t *trail;
-	bool new_mapping;
-	if ((trail = ecache_alloc(tsdn, &arena->pa_shard, ehooks,
-	    &arena->pa_shard.ecache_dirty, edata_past_get(edata), trailsize,
-	    CACHELINE, false, SC_NSIZES, &is_zeroed_trail)) != NULL
-	    || (trail = ecache_alloc(tsdn, &arena->pa_shard, ehooks,
-	    &arena->pa_shard.ecache_muzzy, edata_past_get(edata), trailsize,
-	    CACHELINE, false, SC_NSIZES, &is_zeroed_trail)) != NULL) {
-		if (config_stats) {
-			new_mapping = false;
-		}
-	} else {
-		if ((trail = ecache_alloc_grow(tsdn, &arena->pa_shard, ehooks,
-		    &arena->pa_shard.ecache_retained, edata_past_get(edata),
-		    trailsize, CACHELINE, false, SC_NSIZES, &is_zeroed_trail))
-			== NULL) {
-			return true;
-		}
-		if (config_stats) {
-			new_mapping = true;
-		}
-	}
-
-	if (extent_merge_wrapper(tsdn, ehooks, &arena->pa_shard.edata_cache,
-	    edata, trail)) {
-		extent_dalloc_wrapper(tsdn, &arena->pa_shard, ehooks, trail);
+	size_t mapped_add;
+	bool err = pa_expand(tsdn, &arena->pa_shard, edata, usize,
+	    &is_zeroed_trail, &mapped_add);
+	if (err) {
 		return true;
 	}
 
-	szind_t szind = sz_size2index(usize);
-	emap_remap(tsdn, &emap_global, edata, szind, false);
-
-	if (config_stats && new_mapping) {
-		pa_shard_stats_mapped_add(tsdn, &arena->pa_shard, trailsize);
+	if (config_stats && mapped_add > 0) {
+		pa_shard_stats_mapped_add(tsdn, &arena->pa_shard, mapped_add);
 	}
 
 	if (zero) {
@@ -164,7 +135,7 @@ large_ralloc_no_move_expand(tsdn_t *tsdn, edata_t *edata, size_t usize,
 			 * of CACHELINE in [0 .. PAGE).
 			 */
 			void *zbase = (void *)
-			    ((uintptr_t)edata_addr_get(edata) + oldusize);
+			    ((uintptr_t)edata_addr_get(edata) + old_usize);
 			void *zpast = PAGE_ADDR2BASE((void *)((uintptr_t)zbase +
 			    PAGE));
 			size_t nzero = (uintptr_t)zpast - (uintptr_t)zbase;
@@ -173,7 +144,7 @@ large_ralloc_no_move_expand(tsdn_t *tsdn, edata_t *edata, size_t usize,
 		}
 		assert(is_zeroed_trail);
 	}
-	arena_extent_ralloc_large_expand(tsdn, arena, edata, oldusize);
+	arena_extent_ralloc_large_expand(tsdn, arena, edata, old_usize);
 
 	return false;
 }
diff --git a/src/pa.c b/src/pa.c
index 0dbf0445..7c3b568a 100644
--- a/src/pa.c
+++ b/src/pa.c
@@ -94,3 +94,43 @@ pa_alloc(tsdn_t *tsdn, pa_shard_t *shard, size_t size, size_t alignment,
 	}
 	return edata;
 }
+
+bool
+pa_expand(tsdn_t *tsdn, pa_shard_t *shard, edata_t *edata, size_t new_usize,
+    bool *zero, size_t *mapped_add) {
+	ehooks_t *ehooks = pa_shard_ehooks_get(shard);
+	size_t old_usize = edata_usize_get(edata);
+	size_t trail_size = new_usize - old_usize;
+	void *trail_begin = edata_past_get(edata);
+
+	*mapped_add = 0;
+	if (ehooks_merge_will_fail(ehooks)) {
+		return true;
+	}
+	edata_t *trail = ecache_alloc(tsdn, shard, ehooks, &shard->ecache_dirty,
+	    trail_begin, trail_size, PAGE, /* slab */ false, SC_NSIZES, zero);
+	if (trail == NULL) {
+		trail = ecache_alloc(tsdn, shard, ehooks, &shard->ecache_muzzy,
+		    trail_begin, trail_size, PAGE, /* slab */ false, SC_NSIZES,
+		    zero);
+	}
+	if (trail == NULL) {
+		trail = ecache_alloc_grow(tsdn, shard, ehooks,
+		    &shard->ecache_retained, trail_begin, trail_size, PAGE,
+		    /* slab */ false, SC_NSIZES, zero);
+		*mapped_add = trail_size;
+	}
+	if (trail == NULL) {
+		*mapped_add = 0;
+		return true;
+	}
+	if (extent_merge_wrapper(tsdn, ehooks, &shard->edata_cache, edata,
+	    trail)) {
+		extent_dalloc_wrapper(tsdn, shard, ehooks, trail);
+		*mapped_add = 0;
+		return true;
+	}
+	szind_t szind = sz_size2index(new_usize);
+	emap_remap(tsdn, &emap_global, edata, szind, /* slab */ false);
+	return false;
+}