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ghash: Significantly reduce peak memory use
When resizing, we were keeping both the old and new hash, key and value arrays around while we reinserted entries, resulting in a peak memory overhead of 50%. Using a temporary bookkeeping array with one bit per entry we can now grow and shrink the main arrays using realloc() and an eviction scheme, reducing the overhead to .625% (assuming 64-bit keys and values). Tests show the CPU overhead is negligible.
This commit is contained in:
Hans Petter Jansson
parent
dc983d74cc
commit
7eaf018b29
207
glib/ghash.c
207
glib/ghash.c
@ -374,6 +374,16 @@ g_hash_table_alloc_key_or_value_array (guint size, gboolean is_big G_GNUC_UNUSED
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#endif
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}
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static inline gpointer
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g_hash_table_realloc_key_or_value_array (gpointer a, guint size, gboolean is_big G_GNUC_UNUSED)
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{
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#ifdef USE_SMALL_ARRAYS
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return g_realloc (a, size * (is_big ? BIG_ENTRY_SIZE : SMALL_ENTRY_SIZE));
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#else
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return g_renew (gpointer, a, size);
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#endif
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}
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static inline gpointer
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g_hash_table_fetch_key_or_value (gpointer a, guint index, gboolean is_big)
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{
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@ -395,6 +405,26 @@ g_hash_table_assign_key_or_value (gpointer a, guint index, gboolean is_big, gpoi
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*(((guint *) a) + index) = GPOINTER_TO_UINT (v);
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}
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static inline gpointer
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g_hash_table_evict_key_or_value (gpointer a, guint index, gboolean is_big, gpointer v)
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{
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#ifndef USE_SMALL_ARRAYS
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is_big = TRUE;
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#endif
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if (is_big)
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{
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gpointer r = *(((gpointer *) a) + index);
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*(((gpointer *) a) + index) = v;
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return r;
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}
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else
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{
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gpointer r = GUINT_TO_POINTER (*(((guint *) a) + index));
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*(((guint *) a) + index) = GPOINTER_TO_UINT (v);
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return r;
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}
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}
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static inline guint
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g_hash_table_hash_to_index (GHashTable *hash_table, guint hash)
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{
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@ -642,6 +672,125 @@ g_hash_table_remove_all_nodes (GHashTable *hash_table,
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g_free (old_hashes);
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}
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static void
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realloc_arrays (GHashTable *hash_table, gboolean is_a_set)
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{
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hash_table->hashes = g_renew (guint, hash_table->hashes, hash_table->size);
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hash_table->keys = g_hash_table_realloc_key_or_value_array (hash_table->keys, hash_table->size, hash_table->have_big_keys);
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if (is_a_set)
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hash_table->values = hash_table->keys;
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else
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hash_table->values = g_hash_table_realloc_key_or_value_array (hash_table->values, hash_table->size, hash_table->have_big_values);
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}
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/* When resizing the table in place, we use a temporary bit array to keep
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* track of which entries have been assigned a proper location in the new
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* table layout.
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*
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* Each bit corresponds to a bucket. A bit is set if an entry was assigned
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* its corresponding location during the resize and thus should not be
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* evicted. The array starts out cleared to zero. */
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static inline gboolean
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get_status_bit (const guint32 *bitmap, guint index)
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{
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return (bitmap[index / 32] >> (index % 32)) & 1;
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}
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static inline void
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set_status_bit (guint32 *bitmap, guint index)
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{
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bitmap[index / 32] |= 1 << (index % 32);
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}
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/* By calling dedicated resize functions for sets and maps, we avoid 2x
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* test-and-branch per key in the inner loop. This yields a small
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* performance improvement at the cost of a bit of macro gunk. */
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#define DEFINE_RESIZE_FUNC(fname) \
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static void fname (GHashTable *hash_table, guint old_size, guint32 *reallocated_buckets_bitmap) \
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{ \
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guint i; \
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\
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for (i = 0; i < old_size; i++) \
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{ \
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guint node_hash = hash_table->hashes[i]; \
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gpointer key, value G_GNUC_UNUSED; \
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\
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if (!HASH_IS_REAL (node_hash)) \
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{ \
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/* Clear tombstones */ \
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hash_table->hashes[i] = UNUSED_HASH_VALUE; \
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continue; \
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} \
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\
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/* Skip entries relocated through eviction */ \
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if (get_status_bit (reallocated_buckets_bitmap, i)) \
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continue; \
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\
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hash_table->hashes[i] = UNUSED_HASH_VALUE; \
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EVICT_KEYVAL (hash_table, i, NULL, NULL, key, value); \
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\
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for (;;) \
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{ \
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guint hash_val; \
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guint replaced_hash; \
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guint step = 0; \
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\
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hash_val = g_hash_table_hash_to_index (hash_table, node_hash); \
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\
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while (get_status_bit (reallocated_buckets_bitmap, hash_val)) \
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{ \
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step++; \
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hash_val += step; \
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hash_val &= hash_table->mask; \
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} \
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\
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set_status_bit (reallocated_buckets_bitmap, hash_val); \
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\
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replaced_hash = hash_table->hashes[hash_val]; \
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hash_table->hashes[hash_val] = node_hash; \
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if (!HASH_IS_REAL (replaced_hash)) \
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{ \
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ASSIGN_KEYVAL (hash_table, hash_val, key, value); \
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break; \
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} \
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\
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node_hash = replaced_hash; \
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EVICT_KEYVAL (hash_table, hash_val, key, value, key, value); \
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} \
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} \
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}
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#define ASSIGN_KEYVAL(ht, index, key, value) G_STMT_START{ \
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g_hash_table_assign_key_or_value ((ht)->keys, (index), (ht)->have_big_keys, (key)); \
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g_hash_table_assign_key_or_value ((ht)->values, (index), (ht)->have_big_values, (value)); \
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}G_STMT_END
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#define EVICT_KEYVAL(ht, index, key, value, outkey, outvalue) G_STMT_START{ \
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(outkey) = g_hash_table_evict_key_or_value ((ht)->keys, (index), (ht)->have_big_keys, (key)); \
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(outvalue) = g_hash_table_evict_key_or_value ((ht)->values, (index), (ht)->have_big_values, (value)); \
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}G_STMT_END
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DEFINE_RESIZE_FUNC (resize_map)
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#undef ASSIGN_KEYVAL
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#undef EVICT_KEYVAL
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#define ASSIGN_KEYVAL(ht, index, key, value) G_STMT_START{ \
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g_hash_table_assign_key_or_value ((ht)->keys, (index), (ht)->have_big_keys, (key)); \
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}G_STMT_END
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#define EVICT_KEYVAL(ht, index, key, value, outkey, outvalue) G_STMT_START{ \
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(outkey) = g_hash_table_evict_key_or_value ((ht)->keys, (index), (ht)->have_big_keys, (key)); \
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}G_STMT_END
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DEFINE_RESIZE_FUNC (resize_set)
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#undef ASSIGN_KEYVAL
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#undef EVICT_KEYVAL
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/*
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* g_hash_table_resize:
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* @hash_table: our #GHashTable
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@ -658,54 +807,36 @@ g_hash_table_remove_all_nodes (GHashTable *hash_table,
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static void
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g_hash_table_resize (GHashTable *hash_table)
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{
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gpointer new_keys;
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gpointer new_values;
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guint *new_hashes;
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gint old_size;
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gint i;
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guint32 *reallocated_buckets_bitmap;
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guint old_size;
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gboolean is_a_set;
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old_size = hash_table->size;
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is_a_set = hash_table->keys == hash_table->values;
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g_hash_table_set_shift_from_size (hash_table, hash_table->nnodes * 2);
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new_keys = g_hash_table_alloc_key_or_value_array (hash_table->size, hash_table->have_big_keys);
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if (hash_table->keys == hash_table->values)
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new_values = new_keys;
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else
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new_values = g_hash_table_alloc_key_or_value_array (hash_table->size, hash_table->have_big_values);
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new_hashes = g_new0 (guint, hash_table->size);
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for (i = 0; i < old_size; i++)
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if (hash_table->size > old_size)
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{
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guint node_hash = hash_table->hashes[i];
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guint hash_val;
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guint step = 0;
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realloc_arrays (hash_table, is_a_set);
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memset (&hash_table->hashes[old_size], 0, (hash_table->size - old_size) * sizeof (guint));
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if (!HASH_IS_REAL (node_hash))
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continue;
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hash_val = g_hash_table_hash_to_index (hash_table, node_hash);
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while (!HASH_IS_UNUSED (new_hashes[hash_val]))
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{
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step++;
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hash_val += step;
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hash_val &= hash_table->mask;
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}
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new_hashes[hash_val] = hash_table->hashes[i];
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g_hash_table_assign_key_or_value (new_keys, hash_val, hash_table->have_big_keys, g_hash_table_fetch_key_or_value (hash_table->keys, i, hash_table->have_big_keys));
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g_hash_table_assign_key_or_value (new_values, hash_val, hash_table->have_big_values, g_hash_table_fetch_key_or_value (hash_table->values, i, hash_table->have_big_values));
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reallocated_buckets_bitmap = g_new0 (guint32, (hash_table->size + 31) / 32);
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}
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else
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{
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reallocated_buckets_bitmap = g_new0 (guint32, (old_size + 31) / 32);
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}
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if (hash_table->keys != hash_table->values)
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g_free (hash_table->values);
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if (is_a_set)
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resize_set (hash_table, old_size, reallocated_buckets_bitmap);
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else
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resize_map (hash_table, old_size, reallocated_buckets_bitmap);
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g_free (hash_table->keys);
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g_free (hash_table->hashes);
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g_free (reallocated_buckets_bitmap);
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hash_table->keys = new_keys;
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hash_table->values = new_values;
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hash_table->hashes = new_hashes;
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if (hash_table->size < old_size)
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realloc_arrays (hash_table, is_a_set);
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hash_table->noccupied = hash_table->nnodes;
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}
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