rculfhash: remove now unneeded gc flag (combine with removed)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/rculfhash.c b/rculfhash.c
index 034c7f9053cfbd881496b592cbb3bcddf92a1d8f..1487980c832c115154937cda4b185024636f9e44 100644 (file)
--- a/rculfhash.c
+++ b/rculfhash.c
@@ -194,15 +194,13 @@
 /*
  * The removed flag needs to be updated atomically with the pointer.
  * It indicates that no node must attach to the node scheduled for
- * removal. The gc flag also needs to be updated atomically with the
- * pointer. It indicates that node garbage collection must be performed.
+ * removal, and that node garbage collection must be performed.
  * The dummy flag does not require to be updated atomically with the
  * pointer, but it is added as a pointer low bit flag to save space.
  */
 #define REMOVED_FLAG           (1UL << 0)
-#define GC_FLAG                        (1UL << 1)
-#define DUMMY_FLAG             (1UL << 2)
-#define FLAGS_MASK             ((1UL << 3) - 1)
+#define DUMMY_FLAG             (1UL << 1)
+#define FLAGS_MASK             ((1UL << 2) - 1)
 
 /* Value of the end pointer. Should not interact with flags. */
 #define END_VALUE              NULL
@@ -277,11 +275,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
                                struct cds_lfht_node *node,
                                enum add_mode mode, int dummy);
 
-static
-int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
-               struct cds_lfht_node *node,
-               int dummy_removal, int do_gc);
-
 /*
  * Algorithm to reverse bits in a word by lookup table, extended to
  * 64-bit words.
@@ -676,18 +669,6 @@ struct cds_lfht_node *flag_removed(struct cds_lfht_node *node)
        return (struct cds_lfht_node *) (((unsigned long) node) | REMOVED_FLAG);
 }
 
-static
-int is_gc(struct cds_lfht_node *node)
-{
-       return ((unsigned long) node) & GC_FLAG;
-}
-
-static
-struct cds_lfht_node *flag_gc(struct cds_lfht_node *node)
-{
-       return (struct cds_lfht_node *) (((unsigned long) node) | GC_FLAG);
-}
-
 static
 int is_dummy(struct cds_lfht_node *node)
 {
@@ -743,10 +724,8 @@ void _cds_lfht_gc_bucket(struct cds_lfht_node *dummy, struct cds_lfht_node *node
        struct cds_lfht_node *iter_prev, *iter, *next, *new_next;
 
        assert(!is_dummy(dummy));
-       assert(!is_gc(dummy));
        assert(!is_removed(dummy));
        assert(!is_dummy(node));
-       assert(!is_gc(node));
        assert(!is_removed(node));
        for (;;) {
                iter_prev = dummy;
@@ -766,12 +745,12 @@ void _cds_lfht_gc_bucket(struct cds_lfht_node *dummy, struct cds_lfht_node *node
                        if (likely(clear_flag(iter)->p.reverse_hash > node->p.reverse_hash))
                                return;
                        next = rcu_dereference(clear_flag(iter)->p.next);
-                       if (likely(is_gc(next)))
+                       if (likely(is_removed(next)))
                                break;
                        iter_prev = clear_flag(iter);
                        iter = next;
                }
-               assert(!is_gc(iter));
+               assert(!is_removed(iter));
                if (is_dummy(iter))
                        new_next = flag_dummy(clear_flag(next));
                else
@@ -795,7 +774,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
        unsigned long hash, index, order;
 
        assert(!is_dummy(node));
-       assert(!is_gc(node));
        assert(!is_removed(node));
        if (!size) {
                assert(dummy);
@@ -823,9 +801,8 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
                        if (likely(clear_flag(iter)->p.reverse_hash > node->p.reverse_hash))
                                goto insert;
                        next = rcu_dereference(clear_flag(iter)->p.next);
-                       if (unlikely(is_gc(next)))
+                       if (unlikely(is_removed(next)))
                                goto gc_node;
-                       assert(!is_removed(next));
                        if ((mode == ADD_UNIQUE || mode == ADD_REPLACE)
                            && !is_dummy(next)
                            && !ht->compare_fct(node->key, node->key_len,
@@ -848,8 +825,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
                assert(node != clear_flag(iter));
                assert(!is_removed(iter_prev));
                assert(!is_removed(iter));
-               assert(!is_gc(iter_prev));
-               assert(!is_gc(iter));
                assert(iter_prev != node);
                if (!dummy)
                        node->p.next = clear_flag(iter);
@@ -877,8 +852,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
                assert(node != clear_flag(iter));
                assert(!is_removed(iter_prev));
                assert(!is_removed(iter));
-               assert(!is_gc(iter_prev));
-               assert(!is_gc(iter));
                assert(iter_prev != node);
                assert(!dummy);
                node->p.next = clear_flag(iter);
@@ -890,14 +863,13 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
                 * Here is the whole trick for lock-free replace: we add
                 * the replacement node _after_ the node we want to
                 * replace by atomically setting its next pointer at the
-                * same time we set its removal and gc flags. Given that
+                * same time we set its removal flag. Given that
                 * the lookups/get next use an iterator aware of the
                 * next pointer, they will either skip the old node due
-                * to the removal/gc flag and see the new node, or use
-                * the old new, but will not see the new one.
+                * to the removal flag and see the new node, or use
+                * the old node, but will not see the new one.
                 */
                new_node = flag_removed(new_node);
-               new_node = flag_gc(new_node);
                if (uatomic_cmpxchg(&iter_prev->p.next,
                              iter, new_node) != iter) {
                        continue;       /* retry */
@@ -908,7 +880,6 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht,
 
        gc_node:
                assert(!is_removed(iter));
-               assert(!is_gc(iter));
                if (is_dummy(iter))
                        new_next = flag_dummy(clear_flag(next));
                else
@@ -929,7 +900,7 @@ gc_end:
 static
 int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
                struct cds_lfht_node *node,
-               int dummy_removal, int do_gc)
+               int dummy_removal)
 {
        struct cds_lfht_node *dummy, *next, *old;
        struct _cds_lfht_node *lookup;
@@ -938,7 +909,6 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
 
        /* logically delete the node */
        assert(!is_dummy(node));
-       assert(!is_gc(node));
        assert(!is_removed(node));
        old = rcu_dereference(node->p.next);
        do {
@@ -952,17 +922,12 @@ int _cds_lfht_del(struct cds_lfht *ht, unsigned long size,
                else
                        assert(!is_dummy(next));
                new_next = flag_removed(next);
-               if (do_gc)
-                       new_next = flag_gc(new_next);
                old = uatomic_cmpxchg(&node->p.next, next, new_next);
        } while (old != next);
 
        /* We performed the (logical) deletion. */
        flagged = 1;
 
-       if (!do_gc)
-               goto end;
-
        /*
         * Ensure that the node is not visible to readers anymore: lookup for
         * the node, and remove it (along with any other logically removed node)
@@ -1169,7 +1134,7 @@ void remove_table_partition(struct cds_lfht *ht, unsigned long i,
                fini_node->p.reverse_hash =
                        bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j);
                (void) _cds_lfht_del(ht, !i ? 0 : (1UL << (i - 1)),
-                               fini_node, 1, 1);
+                               fini_node, 1);
                if (CMM_LOAD_SHARED(ht->in_progress_destroy))
                        break;
        }
@@ -1415,7 +1380,7 @@ int cds_lfht_del(struct cds_lfht *ht, struct cds_lfht_node *node)
        int ret;
 
        size = rcu_dereference(ht->t.size);
-       ret = _cds_lfht_del(ht, size, node, 0, 1);
+       ret = _cds_lfht_del(ht, size, node, 0);
        if (!ret)
                ht_count_del(ht, size);
        return ret;
@@ -1436,7 +1401,6 @@ int cds_lfht_delete_dummy(struct cds_lfht *ht)
                if (!is_dummy(node))
                        return -EPERM;
                assert(!is_removed(node));
-               assert(!is_gc(node));
        } while (!is_end(node));
        /*
         * size accessed without rcu_dereference because hash table is
@@ -1497,7 +1461,7 @@ void cds_lfht_count_nodes(struct cds_lfht *ht,
        node = (struct cds_lfht_node *) lookup;
        do {
                next = rcu_dereference(node->p.next);
-               if (is_removed(next) || is_gc(next)) {
+               if (is_removed(next)) {
                        assert(!is_dummy(next));
                        (*removed)++;
                } else if (!is_dummy(next))

diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h
index c3c1cbc2b797afbbc022f1bedbc146abd7cdb61e..7afd6244a97df896cc54af017e8f217edda926a5 100644 (file)
--- a/urcu/rculfhash.h
+++ b/urcu/rculfhash.h
@@ -34,11 +34,11 @@ extern "C" {
 
 /*
  * struct cds_lfht_node and struct _cds_lfht_node should be aligned on
- * 8-bytes boundaries because the two lower bits are used as flags.
+ * 4-bytes boundaries because the two lower bits are used as flags.
  */
 
 struct _cds_lfht_node {
-       struct cds_lfht_node *next;     /* ptr | DUMMY_FLAG | GC_FLAG | REMOVED_FLAG */
+       struct cds_lfht_node *next;     /* ptr | DUMMY_FLAG | REMOVED_FLAG */
        unsigned long reverse_hash;
 } __attribute__((aligned(8)));