rhashtable: Shrink to fit

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>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index 798f01d64ab0135e602a518f93801d7be34ab3f7..9623be345d9cbff90955194f9306986f4676cc8b 100644 (file)
--- 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;