Add extent serial numbers.

Add extent serial numbers and use them where appropriate as a sort key
that is higher priority than address, so that the allocation policy
prefers older extents.

This resolves #147.

src/arena.c

@@ -760,7 +760,7 @@ arena_purge_to_limit(tsdn_t *tsdn, arena_t *arena, size_t ndirty_limit)
 		size_t ndirty = arena_dirty_count(tsdn, arena);
 		assert(ndirty == arena->ndirty);
 	}
-	extent_init(&purge_extents_sentinel, arena, NULL, 0, 0, false, false,
+	extent_init(&purge_extents_sentinel, arena, NULL, 0, 0, 0, false, false,
 	    false, false);
 
 	npurge = arena_stash_dirty(tsdn, arena, &extent_hooks, ndirty_limit,
@@ -1351,12 +1351,12 @@ arena_bin_lower_slab(tsdn_t *tsdn, arena_t *arena, extent_t *slab,
 	assert(extent_slab_data_get(slab)->nfree > 0);
 
 	/*
-	 * Make sure that if bin->slabcur is non-NULL, it refers to the lowest
-	 * non-full slab.  It is okay to NULL slabcur out rather than
-	 * proactively keeping it pointing at the lowest non-full slab.
+	 * Make sure that if bin->slabcur is non-NULL, it refers to the
+	 * oldest/lowest non-full slab.  It is okay to NULL slabcur out rather
+	 * than proactively keeping it pointing at the oldest/lowest non-full
+	 * slab.
 	 */
-	if (bin->slabcur != NULL && (uintptr_t)extent_addr_get(slab) <
-	    (uintptr_t)extent_addr_get(bin->slabcur)) {
+	if (bin->slabcur != NULL && extent_snad_comp(bin->slabcur, slab) > 0) {
 		/* Switch slabcur. */
 		if (extent_slab_data_get(bin->slabcur)->nfree > 0)
 			arena_bin_slabs_nonfull_insert(bin, bin->slabcur);
@@ -1651,6 +1651,13 @@ arena_nthreads_dec(arena_t *arena, bool internal)
 	atomic_sub_u(&arena->nthreads[internal], 1);
 }
 
+size_t
+arena_extent_sn_next(arena_t *arena)
+{
+
+	return (atomic_add_zu(&arena->extent_sn_next, 1) - 1);
+}
+
 arena_t *
 arena_new(tsdn_t *tsdn, unsigned ind)
 {
@@ -1684,6 +1691,8 @@ arena_new(tsdn_t *tsdn, unsigned ind)
 		    (size_t)(uintptr_t)arena;
 	}
 
+	arena->extent_sn_next = 0;
+
 	arena->dss_prec = extent_dss_prec_get();
 
 	arena->purging = false;
@@ -1702,7 +1711,7 @@ arena_new(tsdn_t *tsdn, unsigned ind)
 		extent_heap_new(&arena->extents_retained[i]);
 	}
 
-	extent_init(&arena->extents_dirty, arena, NULL, 0, 0, false, false,
+	extent_init(&arena->extents_dirty, arena, NULL, 0, 0, 0, false, false,
 	    false, false);
 
 	if (malloc_mutex_init(&arena->extents_mtx, "arena_extents",
@@ -1724,8 +1733,8 @@ arena_new(tsdn_t *tsdn, unsigned ind)
 			return (NULL);
 		bin->slabcur = NULL;
 		extent_heap_new(&bin->slabs_nonfull);
-		extent_init(&bin->slabs_full, arena, NULL, 0, 0, false, false,
-		    false, false);
+		extent_init(&bin->slabs_full, arena, NULL, 0, 0, 0, false,
+		    false, false, false);
 		if (config_stats)
 			memset(&bin->stats, 0, sizeof(malloc_bin_stats_t));
 	}

src/base.c

@@ -5,6 +5,7 @@
 /* Data. */
 
 static malloc_mutex_t	base_mtx;
+static size_t		base_extent_sn_next;
 static extent_heap_t	base_avail[NSIZES];
 static extent_t		*base_extents;
 static size_t		base_allocated;
@@ -37,6 +38,14 @@ base_extent_dalloc(tsdn_t *tsdn, extent_t *extent)
 	base_extents = extent;
 }
 
+static void
+base_extent_init(extent_t *extent, void *addr, size_t size)
+{
+	size_t sn = atomic_add_zu(&base_extent_sn_next, 1) - 1;
+
+	extent_init(extent, NULL, addr, size, 0, sn, true, true, true, false);
+}
+
 static extent_t *
 base_extent_alloc(tsdn_t *tsdn, size_t minsize)
 {
@@ -74,7 +83,7 @@ base_extent_alloc(tsdn_t *tsdn, size_t minsize)
 			base_resident += PAGE_CEILING(nsize);
 		}
 	}
-	extent_init(extent, NULL, addr, esize, 0, true, true, true, false);
+	base_extent_init(extent, addr, esize);
 	return (extent);
 }
 
@@ -164,6 +173,7 @@ base_boot(void)
 
 	if (malloc_mutex_init(&base_mtx, "base", WITNESS_RANK_BASE))
 		return (true);
+	base_extent_sn_next = 0;
 	for (i = 0; i < NSIZES; i++)
 		extent_heap_new(&base_avail[i]);
 	base_extents = NULL;

src/extent.c

@@ -177,17 +177,8 @@ extent_size_quantize_t *extent_size_quantize_ceil =
     JEMALLOC_N(n_extent_size_quantize_ceil);
 #endif
 
-JEMALLOC_INLINE_C int
-extent_ad_comp(const extent_t *a, const extent_t *b)
-{
-	uintptr_t a_addr = (uintptr_t)extent_addr_get(a);
-	uintptr_t b_addr = (uintptr_t)extent_addr_get(b);
-
-	return ((a_addr > b_addr) - (a_addr < b_addr));
-}
-
 /* Generate pairing heap functions. */
-ph_gen(, extent_heap_, extent_heap_t, extent_t, ph_link, extent_ad_comp)
+ph_gen(, extent_heap_, extent_heap_t, extent_t, ph_link, extent_snad_comp)
 
 static void
 extent_heaps_insert(tsdn_t *tsdn, extent_heap_t extent_heaps[NPSIZES+1],
@@ -353,8 +344,8 @@ extent_deregister(tsdn_t *tsdn, extent_t *extent)
 }
 
 /*
- * Do first-best-fit extent selection, i.e. select the lowest extent that best
- * fits.
+ * Do first-best-fit extent selection, i.e. select the oldest/lowest extent that
+ * best fits.
  */
 static extent_t *
 extent_first_best_fit(tsdn_t *tsdn, arena_t *arena,
@@ -708,7 +699,8 @@ extent_alloc_wrapper_hard(tsdn_t *tsdn, arena_t *arena,
 		extent_dalloc(tsdn, arena, extent);
 		return (NULL);
 	}
-	extent_init(extent, arena, addr, size, usize, true, zero, commit, slab);
+	extent_init(extent, arena, addr, size, usize,
+	    arena_extent_sn_next(arena), true, zero, commit, slab);
 	if (pad != 0)
 		extent_addr_randomize(tsdn, extent, alignment);
 	if (extent_register(tsdn, extent)) {
@@ -1036,7 +1028,7 @@ extent_split_wrapper(tsdn_t *tsdn, arena_t *arena,
 		extent_t lead;
 
 		extent_init(&lead, arena, extent_addr_get(extent), size_a,
-		    usize_a, extent_active_get(extent),
+		    usize_a, extent_sn_get(extent), extent_active_get(extent),
 		    extent_zeroed_get(extent), extent_committed_get(extent),
 		    extent_slab_get(extent));
 
@@ -1046,9 +1038,9 @@ extent_split_wrapper(tsdn_t *tsdn, arena_t *arena,
 	}
 
 	extent_init(trail, arena, (void *)((uintptr_t)extent_base_get(extent) +
-	    size_a), size_b, usize_b, extent_active_get(extent),
-	    extent_zeroed_get(extent), extent_committed_get(extent),
-	    extent_slab_get(extent));
+	    size_a), size_b, usize_b, extent_sn_get(extent),
+	    extent_active_get(extent), extent_zeroed_get(extent),
+	    extent_committed_get(extent), extent_slab_get(extent));
 	if (extent_rtree_acquire(tsdn, rtree_ctx, trail, false, true,
 	    &trail_elm_a, &trail_elm_b))
 		goto label_error_c;
@@ -1145,6 +1137,8 @@ extent_merge_wrapper(tsdn_t *tsdn, arena_t *arena,
 
 	extent_size_set(a, extent_size_get(a) + extent_size_get(b));
 	extent_usize_set(a, extent_usize_get(a) + extent_usize_get(b));
+	extent_sn_set(a, (extent_sn_get(a) < extent_sn_get(b)) ?
+	    extent_sn_get(a) : extent_sn_get(b));
 	extent_zeroed_set(a, extent_zeroed_get(a) && extent_zeroed_get(b));
 
 	extent_rtree_write_acquired(tsdn, a_elm_a, b_elm_b, a);

src/extent_dss.c

@@ -142,7 +142,8 @@ extent_alloc_dss(tsdn_t *tsdn, arena_t *arena, void *new_addr, size_t size,
 			gap_size = (uintptr_t)ret - (uintptr_t)gap_addr;
 			if (gap_size != 0) {
 				extent_init(gap, arena, gap_addr, gap_size,
-				    gap_size, false, false, true, false);
+				    gap_size, arena_extent_sn_next(arena),
+				    false, false, true, false);
 			}
 			dss_next = (void *)((uintptr_t)ret + size);
 			if ((uintptr_t)ret < (uintptr_t)max_cur ||