From: Mathieu Desnoyers Date: Wed, 7 Sep 2011 22:50:05 +0000 (-0700) Subject: rculfhash: allow shrink X-Git-Tag: v0.7.0~43^2~174 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=1475579ca651164ea74eb0c9f727baad991098af;p=urcu.git rculfhash: allow shrink Signed-off-by: Mathieu Desnoyers --- diff --git a/rculfhash.c b/rculfhash.c index 20d389d..cd60f5f 100644 --- a/rculfhash.c +++ b/rculfhash.c @@ -1,7 +1,7 @@ /* * rculfhash.c * - * Userspace RCU library - Lock-Free Expandable RCU Hash Table + * Userspace RCU library - Lock-Free Resizable RCU Hash Table * * Copyright 2010-2011 - Mathieu Desnoyers * @@ -29,7 +29,7 @@ * symposium on Parallel algorithms and architectures, ACM Press, * (2002), 73-82. * - * Some specificities of this Lock-Free Expandable RCU Hash Table + * Some specificities of this Lock-Free Resizable RCU Hash Table * implementation: * * - RCU read-side critical section allows readers to perform hash @@ -48,9 +48,13 @@ * - An index of dummy nodes is kept. These dummy nodes are the hash * table "buckets", and they are also chained together in the * split-ordered list, which allows recursive expansion. - * - The resize operation only allows expanding the hash table. - * It is triggered either through an API call or automatically by - * detecting long chains in the add operation. + * - The resize operation for small tables only allows expanding the hash table. + * It is triggered automatically by detecting long chains in the add + * operation. + * - The resize operation for larger tables (and available through an + * API) allows both expanding and shrinking the hash table. + * - Per-CPU Split-counters are used to keep track of the number of + * nodes within the hash table for automatic resize triggering. * - Resize operation initiated by long chain detection is executed by a * call_rcu thread, which keeps lock-freedom of add and remove. * - Resize operations are protected by a mutex. @@ -92,6 +96,39 @@ * - The per-order dummy node tables contain a compact version of the * hash table nodes. These tables are invariant after they are * populated into the hash table. + * + * A bit of ascii art explanation: + * + * Order index is the off-by-one compare to the actual power of 2 because + * we use index 0 to deal with the 0 special-case. + * + * This shows the nodes for a small table ordered by reversed bits: + * + * bits reverse + * 0 000 000 + * 4 100 001 + * 2 010 010 + * 6 110 011 + * 1 001 100 + * 5 101 101 + * 3 011 110 + * 7 111 111 + * + * This shows the nodes in order of non-reversed bits, linked by + * reversed-bit order. + * + * order bits reverse + * 0 0 000 000 + * | + * 1 | 1 001 100 <- + * | | | + * 2 | | 2 010 010 | + * | | | 3 011 110 <- | + * | | | | | | + * 3 -> | | | 4 100 001 | | + * -> | | 5 101 101 | + * -> | 6 110 011 + * -> 7 111 111 */ #define _LGPL_SOURCE @@ -146,12 +183,17 @@ struct ht_items_count { unsigned long add, remove; } __attribute__((aligned(CAA_CACHE_LINE_SIZE))); +struct rcu_level { + struct rcu_head head; + struct _cds_lfht_node nodes[0]; +}; + struct rcu_table { unsigned long size; /* always a power of 2 */ unsigned long resize_target; int resize_initiated; struct rcu_head head; - struct _cds_lfht_node *tbl[0]; + struct rcu_level *tbl[0]; }; struct cds_lfht { @@ -163,6 +205,7 @@ struct cds_lfht { unsigned int in_progress_resize, in_progress_destroy; void (*cds_lfht_call_rcu)(struct rcu_head *head, void (*func)(struct rcu_head *head)); + void (*cds_lfht_synchronize_rcu)(void); unsigned long count; /* global approximate item count */ struct ht_items_count *percpu_count; /* per-cpu item count */ }; @@ -583,6 +626,22 @@ unsigned long _uatomic_max(unsigned long *ptr, unsigned long v) return v; } +static +void cds_lfht_free_table_cb(struct rcu_head *head) +{ + struct rcu_table *t = + caa_container_of(head, struct rcu_table, head); + free(t); +} + +static +void cds_lfht_free_level(struct rcu_head *head) +{ + struct rcu_level *l = + caa_container_of(head, struct rcu_level, head); + free(l); +} + /* * Remove all logically deleted nodes from a bucket up to a certain node key. */ @@ -640,7 +699,7 @@ struct cds_lfht_node *_cds_lfht_add(struct cds_lfht *ht, struct rcu_table *t, */ index = hash & (t->size - 1); order = get_count_order_ulong(index + 1); - lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)]; iter_prev = (struct cds_lfht_node *) lookup; /* We can always skip the dummy node initially */ iter = rcu_dereference(iter_prev->p.next); @@ -696,7 +755,7 @@ gc_end: /* Garbage collect logically removed nodes in the bucket */ index = hash & (t->size - 1); order = get_count_order_ulong(index + 1); - lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)]; dummy_node = (struct cds_lfht_node *) lookup; _cds_lfht_gc_bucket(dummy_node, node); return node; @@ -704,7 +763,7 @@ gc_end: static int _cds_lfht_remove(struct cds_lfht *ht, struct rcu_table *t, - struct cds_lfht_node *node) + struct cds_lfht_node *node, int dummy_removal) { struct cds_lfht_node *dummy, *next, *old; struct _cds_lfht_node *lookup; @@ -717,7 +776,10 @@ int _cds_lfht_remove(struct cds_lfht *ht, struct rcu_table *t, next = old; if (unlikely(is_removed(next))) goto end; - assert(!is_dummy(next)); + if (dummy_removal) + assert(is_dummy(next)); + else + assert(!is_dummy(next)); old = uatomic_cmpxchg(&node->p.next, next, flag_removed(next)); } while (old != next); @@ -725,15 +787,27 @@ int _cds_lfht_remove(struct cds_lfht *ht, struct rcu_table *t, /* We performed the (logical) deletion. */ flagged = 1; + if (dummy_removal) + node = clear_flag(node); + /* * Ensure that the node is not visible to readers anymore: lookup for * the node, and remove it (along with any other logically removed node) * if found. */ hash = bit_reverse_ulong(node->p.reverse_hash); - index = hash & (t->size - 1); + /* + * When removing a dummy node, we need to consider the lower + * order table, so we don't end up looking up the dummy nodes we + * are currently removing. + */ + + if (dummy_removal) + index = hash & ((t->size >> 1) - 1); + else + index = hash & (t->size - 1); order = get_count_order_ulong(index + 1); - lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)]; dummy = (struct cds_lfht_node *) lookup; _cds_lfht_gc_bucket(dummy, node); end: @@ -763,12 +837,14 @@ void init_table(struct cds_lfht *ht, struct rcu_table *t, len = !i ? 1 : 1UL << (i - 1); dbg_printf("init order %lu len: %lu\n", i, len); - t->tbl[i] = calloc(len, sizeof(struct _cds_lfht_node)); + t->tbl[i] = calloc(1, sizeof(struct rcu_level) + + (len * sizeof(struct _cds_lfht_node))); for (j = 0; j < len; j++) { + struct cds_lfht_node *new_node = + (struct cds_lfht_node *) &t->tbl[i]->nodes[j]; + dbg_printf("init entry: i %lu j %lu hash %lu\n", i, j, !i ? 0 : (1UL << (i - 1)) + j); - struct cds_lfht_node *new_node = - (struct cds_lfht_node *) &t->tbl[i][j]; new_node->p.reverse_hash = bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j); (void) _cds_lfht_add(ht, t, new_node, 0, 1); @@ -785,12 +861,53 @@ void init_table(struct cds_lfht *ht, struct rcu_table *t, t->resize_initiated = 0; } +static +void fini_table(struct cds_lfht *ht, struct rcu_table *t, + unsigned long first_order, unsigned long len_order) +{ + long i, end_order; + + dbg_printf("fini table: first_order %lu end_order %lu\n", + first_order, first_order + len_order); + end_order = first_order + len_order; + assert(first_order > 0); + assert(t->size == (1UL << (end_order - 1))); + for (i = end_order - 1; i >= first_order; i--) { + unsigned long j, len; + + len = !i ? 1 : 1UL << (i - 1); + dbg_printf("fini order %lu len: %lu\n", i, len); + /* Unlink */ + for (j = 0; j < len; j++) { + struct cds_lfht_node *new_node = + (struct cds_lfht_node *) &t->tbl[i]->nodes[j]; + + dbg_printf("fini entry: i %lu j %lu hash %lu\n", + i, j, !i ? 0 : (1UL << (i - 1)) + j); + new_node->p.reverse_hash = + bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j); + (void) _cds_lfht_remove(ht, t, new_node, 1); + if (CMM_LOAD_SHARED(ht->in_progress_destroy)) + break; + } + ht->cds_lfht_call_rcu(&t->tbl[i]->head, cds_lfht_free_level); + /* Update table size */ + t->size = (i == 1) ? 0 : 1UL << (i - 2); + dbg_printf("fini new size: %lu\n", t->size); + if (CMM_LOAD_SHARED(ht->in_progress_destroy)) + break; + } + t->resize_target = t->size; + t->resize_initiated = 0; +} + struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct, cds_lfht_compare_fct compare_fct, unsigned long hash_seed, unsigned long init_size, void (*cds_lfht_call_rcu)(struct rcu_head *head, - void (*func)(struct rcu_head *head))) + void (*func)(struct rcu_head *head)), + void (*cds_lfht_synchronize_rcu)(void)) { struct cds_lfht *ht; unsigned long order; @@ -803,13 +920,14 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct, ht->compare_fct = compare_fct; ht->hash_seed = hash_seed; ht->cds_lfht_call_rcu = cds_lfht_call_rcu; + ht->cds_lfht_synchronize_rcu = cds_lfht_synchronize_rcu; ht->in_progress_resize = 0; ht->percpu_count = alloc_per_cpu_items_count(); /* this mutex should not nest in read-side C.S. */ pthread_mutex_init(&ht->resize_mutex, NULL); order = get_count_order_ulong(max(init_size, 1)) + 1; ht->t = calloc(1, sizeof(struct cds_lfht) - + (order * sizeof(struct _cds_lfht_node *))); + + (order * sizeof(struct rcu_level *))); ht->t->size = 0; pthread_mutex_lock(&ht->resize_mutex); init_table(ht, ht->t, 0, order); @@ -830,7 +948,7 @@ struct cds_lfht_node *cds_lfht_lookup(struct cds_lfht *ht, void *key, size_t key t = rcu_dereference(ht->t); index = hash & (t->size - 1); order = get_count_order_ulong(index + 1); - lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + lookup = &t->tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)]; dbg_printf("lookup hash %lu index %lu order %lu aridx %lu\n", hash, index, order, index & ((1UL << (order - 1)) - 1)); node = (struct cds_lfht_node *) lookup; @@ -922,7 +1040,7 @@ int cds_lfht_remove(struct cds_lfht *ht, struct cds_lfht_node *node) int ret; t = rcu_dereference(ht->t); - ret = _cds_lfht_remove(ht, t, node); + ret = _cds_lfht_remove(ht, t, node, 0); if (!ret) ht_count_remove(ht, t); return ret; @@ -938,7 +1056,7 @@ int cds_lfht_delete_dummy(struct cds_lfht *ht) t = ht->t; /* Check that the table is empty */ - lookup = &t->tbl[0][0]; + lookup = &t->tbl[0]->nodes[0]; node = (struct cds_lfht_node *) lookup; do { node = clear_flag(node)->p.next; @@ -954,8 +1072,8 @@ int cds_lfht_delete_dummy(struct cds_lfht *ht) for (i = 0; i < len; i++) { dbg_printf("delete order %lu i %lu hash %lu\n", order, i, - bit_reverse_ulong(t->tbl[order][i].reverse_hash)); - assert(is_dummy(t->tbl[order][i].next)); + bit_reverse_ulong(t->tbl[order]->nodes[i].reverse_hash)); + assert(is_dummy(t->tbl[order]->nodes[i].next)); } free(t->tbl[order]); } @@ -997,7 +1115,7 @@ void cds_lfht_count_nodes(struct cds_lfht *ht, t = rcu_dereference(ht->t); /* Count non-dummy nodes in the table */ - lookup = &t->tbl[0][0]; + lookup = &t->tbl[0]->nodes[0]; node = (struct cds_lfht_node *) lookup; do { next = rcu_dereference(node->p.next); @@ -1013,42 +1131,85 @@ void cds_lfht_count_nodes(struct cds_lfht *ht, dbg_printf("number of dummy nodes: %lu\n", nr_dummy); } +/* called with resize mutex held */ static -void cds_lfht_free_table_cb(struct rcu_head *head) +void _do_cds_lfht_grow(struct cds_lfht *ht, struct rcu_table *old_t, + unsigned long old_size, unsigned long new_size) { - struct rcu_table *t = - caa_container_of(head, struct rcu_table, head); - free(t); + unsigned long old_order, new_order; + struct rcu_table *new_t; + + old_order = get_count_order_ulong(old_size) + 1; + new_order = get_count_order_ulong(new_size) + 1; + printf("resize from %lu (order %lu) to %lu (order %lu) buckets\n", + old_size, old_order, new_size, new_order); + new_t = malloc(sizeof(struct cds_lfht) + + (new_order * sizeof(struct rcu_level *))); + assert(new_size > old_size); + memcpy(&new_t->tbl, &old_t->tbl, + old_order * sizeof(struct rcu_level *)); + init_table(ht, new_t, old_order, new_order - old_order); + /* Changing table and size atomically wrt lookups */ + rcu_assign_pointer(ht->t, new_t); + ht->cds_lfht_call_rcu(&old_t->head, cds_lfht_free_table_cb); } /* called with resize mutex held */ static -void _do_cds_lfht_resize(struct cds_lfht *ht) +void _do_cds_lfht_shrink(struct cds_lfht *ht, struct rcu_table *old_t, + unsigned long old_size, unsigned long new_size) { - unsigned long new_size, old_size, old_order, new_order; - struct rcu_table *new_t, *old_t; + unsigned long old_order, new_order; + struct rcu_table *new_t; - old_t = ht->t; - old_size = old_t->size; + new_size = max(new_size, 1); old_order = get_count_order_ulong(old_size) + 1; - - new_size = CMM_LOAD_SHARED(old_t->resize_target); - if (old_size == new_size) - return; new_order = get_count_order_ulong(new_size) + 1; printf("resize from %lu (order %lu) to %lu (order %lu) buckets\n", old_size, old_order, new_size, new_order); new_t = malloc(sizeof(struct cds_lfht) - + (new_order * sizeof(struct _cds_lfht_node *))); - assert(new_size > old_size); + + (new_order * sizeof(struct rcu_level *))); + assert(new_size < old_size); memcpy(&new_t->tbl, &old_t->tbl, - old_order * sizeof(struct _cds_lfht_node *)); - init_table(ht, new_t, old_order, new_order - old_order); + new_order * sizeof(struct rcu_level *)); + new_t->size = !new_order ? 1 : (1UL << (new_order - 1)); + new_t->resize_target = new_t->size; + new_t->resize_initiated = 0; + /* Changing table and size atomically wrt lookups */ rcu_assign_pointer(ht->t, new_t); + + /* + * We need to wait for all reader threads to reach Q.S. (and + * thus use the new table for lookups) before we can start + * releasing the old dummy nodes. + */ + ht->cds_lfht_synchronize_rcu(); + + /* Unlink and remove all now-unused dummy node pointers. */ + fini_table(ht, old_t, new_order, old_order - new_order); ht->cds_lfht_call_rcu(&old_t->head, cds_lfht_free_table_cb); } + +/* called with resize mutex held */ +static +void _do_cds_lfht_resize(struct cds_lfht *ht) +{ + unsigned long new_size, old_size; + struct rcu_table *old_t; + + old_t = ht->t; + old_size = old_t->size; + new_size = CMM_LOAD_SHARED(old_t->resize_target); + if (old_size < new_size) + _do_cds_lfht_grow(ht, old_t, old_size, new_size); + else if (old_size > new_size) + _do_cds_lfht_shrink(ht, old_t, old_size, new_size); + else + CMM_STORE_SHARED(old_t->resize_initiated, 0); +} + static unsigned long resize_target_update(struct rcu_table *t, int growth_order) @@ -1057,26 +1218,24 @@ unsigned long resize_target_update(struct rcu_table *t, t->size << growth_order); } -void cds_lfht_resize(struct cds_lfht *ht, int growth) +static +unsigned long resize_target_update_count(struct rcu_table *t, + unsigned long count) +{ + count = max(count, 1); + return uatomic_set(&t->resize_target, count); +} + +void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size) { struct rcu_table *t = rcu_dereference(ht->t); unsigned long target_size; - if (growth < 0) { - /* - * Silently refuse to shrink hash table. (not supported) - */ - dbg_printf("shrinking hash table not supported.\n"); - return; - } - - target_size = resize_target_update(t, growth); - if (t->size < target_size) { - CMM_STORE_SHARED(t->resize_initiated, 1); - pthread_mutex_lock(&ht->resize_mutex); - _do_cds_lfht_resize(ht); - pthread_mutex_unlock(&ht->resize_mutex); - } + target_size = resize_target_update_count(t, new_size); + CMM_STORE_SHARED(t->resize_initiated, 1); + pthread_mutex_lock(&ht->resize_mutex); + _do_cds_lfht_resize(ht); + pthread_mutex_unlock(&ht->resize_mutex); } static @@ -1113,13 +1272,6 @@ void cds_lfht_resize_lazy(struct cds_lfht *ht, struct rcu_table *t, int growth) #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) -static -unsigned long resize_target_update_count(struct rcu_table *t, - unsigned long count) -{ - return uatomic_set(&t->resize_target, count); -} - static void cds_lfht_resize_lazy_count(struct cds_lfht *ht, struct rcu_table *t, unsigned long count) @@ -1128,7 +1280,7 @@ void cds_lfht_resize_lazy_count(struct cds_lfht *ht, struct rcu_table *t, unsigned long target_size; target_size = resize_target_update_count(t, count); - if (!CMM_LOAD_SHARED(t->resize_initiated) && t->size < target_size) { + if (!CMM_LOAD_SHARED(t->resize_initiated)) { uatomic_inc(&ht->in_progress_resize); cmm_smp_mb(); /* increment resize count before calling it */ work = malloc(sizeof(*work)); diff --git a/tests/test_urcu_hash.c b/tests/test_urcu_hash.c index 8016912..fc2cfb2 100644 --- a/tests/test_urcu_hash.c +++ b/tests/test_urcu_hash.c @@ -697,7 +697,7 @@ int main(int argc, char **argv) count_reader = malloc(sizeof(*count_reader) * nr_readers); count_writer = malloc(sizeof(*count_writer) * nr_writers); test_ht = cds_lfht_new(test_hash, test_compare, 0x42UL, - init_hash_size, call_rcu); + init_hash_size, call_rcu, synchronize_rcu); ret = populate_hash(); assert(!ret); err = create_all_cpu_call_rcu_data(0); diff --git a/urcu/rculfhash.h b/urcu/rculfhash.h index 37e36b7..ad157bb 100644 --- a/urcu/rculfhash.h +++ b/urcu/rculfhash.h @@ -83,7 +83,8 @@ struct cds_lfht *cds_lfht_new(cds_lfht_hash_fct hash_fct, unsigned long hash_seed, unsigned long init_size, void (*cds_lfht_call_rcu)(struct rcu_head *head, - void (*func)(struct rcu_head *head))); + void (*func)(struct rcu_head *head)), + void (*cds_lfht_synchronize_rcu)(void)); /* * cds_lfht_destroy - destroy a hash table. @@ -147,11 +148,9 @@ int cds_lfht_remove(struct cds_lfht *ht, struct cds_lfht_node *node); /* * cds_lfht_resize - Force a hash table resize - * @growth: growth order (current size is multiplied by 2^growth) - * - * Currently, only expand operation is supported (growth >= 0). + * @new_size: update to this hash table size. */ -void cds_lfht_resize(struct cds_lfht *ht, int growth); +void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size); #ifdef __cplusplus }