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authorHerbert Xu <herbert@gondor.apana.org.au>2015-05-15 11:30:47 +0800
committerDavid S. Miller <davem@davemloft.net>2015-05-16 18:08:26 -0400
commit07ee0722bf941960fb3888f9c9b5839473372fd1 (patch)
treed80ad157b570da14e08e25bb32c5d58af5d969c3 /include
parentdb9683fb412d4af33f66b9fe3d8dace1c6d113c9 (diff)
rhashtable: Add cap on number of elements in hash table
We currently have no limit on the number of elements in a hash table. This is a problem because some users (tipc) set a ceiling on the maximum table size and when that is reached the hash table may degenerate. Others may encounter OOM when growing and if we allow insertions when that happens the hash table perofrmance may also suffer. This patch adds a new paramater insecure_max_entries which becomes the cap on the table. If unset it defaults to max_size * 2. If it is also zero it means that there is no cap on the number of elements in the table. However, the table will grow whenever the utilisation hits 100% and if that growth fails, you will get ENOMEM on insertion. As allowing oversubscription is potentially dangerous, the name contains the word insecure. Note that the cap is not a hard limit. This is done for performance reasons as enforcing a hard limit will result in use of atomic ops that are heavier than the ones we currently use. The reasoning is that we're only guarding against a gross over- subscription of the table, rather than a small breach of the limit. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include')
-rw-r--r--include/linux/rhashtable.h19
1 files changed, 19 insertions, 0 deletions
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index dbcbcc59aa92..843ceca9a21e 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -17,6 +17,7 @@
#ifndef _LINUX_RHASHTABLE_H
#define _LINUX_RHASHTABLE_H
+#include <linux/atomic.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/jhash.h>
@@ -100,6 +101,7 @@ struct rhashtable;
* @key_len: Length of key
* @key_offset: Offset of key in struct to be hashed
* @head_offset: Offset of rhash_head in struct to be hashed
+ * @insecure_max_entries: Maximum number of entries (may be exceeded)
* @max_size: Maximum size while expanding
* @min_size: Minimum size while shrinking
* @nulls_base: Base value to generate nulls marker
@@ -115,6 +117,7 @@ struct rhashtable_params {
size_t key_len;
size_t key_offset;
size_t head_offset;
+ unsigned int insecure_max_entries;
unsigned int max_size;
unsigned int min_size;
u32 nulls_base;
@@ -286,6 +289,18 @@ static inline bool rht_grow_above_100(const struct rhashtable *ht,
(!ht->p.max_size || tbl->size < ht->p.max_size);
}
+/**
+ * rht_grow_above_max - returns true if table is above maximum
+ * @ht: hash table
+ * @tbl: current table
+ */
+static inline bool rht_grow_above_max(const struct rhashtable *ht,
+ const struct bucket_table *tbl)
+{
+ return ht->p.insecure_max_entries &&
+ atomic_read(&ht->nelems) >= ht->p.insecure_max_entries;
+}
+
/* The bucket lock is selected based on the hash and protects mutations
* on a group of hash buckets.
*
@@ -589,6 +604,10 @@ restart:
goto out;
}
+ err = -E2BIG;
+ if (unlikely(rht_grow_above_max(ht, tbl)))
+ goto out;
+
if (unlikely(rht_grow_above_100(ht, tbl))) {
slow_path:
spin_unlock_bh(lock);