[v3 PATCH 6/9] rhashtable: Shrink to fit
From: Herbert Xu <herbert@gondor.apana.org.au>
Date: 2015-03-23 13:50:44
Subsystem:
library code, rhashtable, the rest · Maintainers:
Andrew Morton, Thomas Graf, Herbert Xu, Linus Torvalds
This patch changes rhashtable_shrink to shrink to the smallest size possible rather than halving the table. This is needed because with multiple rehashing we will defer shrinking until all other rehashing is done, meaning that when we do shrink we may be able to shrink a lot. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> --- lib/rhashtable.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 798f01d..9623be3 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c@@ -261,8 +261,8 @@ EXPORT_SYMBOL_GPL(rhashtable_expand); * rhashtable_shrink - Shrink hash table while allowing concurrent lookups * @ht: the hash table to shrink * - * This function may only be called in a context where it is safe to call - * synchronize_rcu(), e.g. not within a rcu_read_lock() section. + * This function shrinks the hash table to fit, i.e., the smallest + * size would not cause it to expand right away automatically. * * The caller must ensure that no concurrent resizing occurs by holding * ht->mutex.
@@ -276,10 +276,17 @@ EXPORT_SYMBOL_GPL(rhashtable_expand); int rhashtable_shrink(struct rhashtable *ht) { struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht); + unsigned size = roundup_pow_of_two(atomic_read(&ht->nelems) * 3 / 2); ASSERT_RHT_MUTEX(ht); - new_tbl = bucket_table_alloc(ht, old_tbl->size / 2); + if (size < ht->p.min_size) + size = ht->p.min_size; + + if (old_tbl->size <= size) + return 0; + + new_tbl = bucket_table_alloc(ht, size); if (new_tbl == NULL) return -ENOMEM;