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authorEric Dumazet <dada1@cosmosbay.com>2008-11-16 19:37:55 -0800
committerDavid S. Miller <davem@davemloft.net>2008-11-16 19:37:55 -0800
commitbbaffaca4810de1a25e32ecaf836eeaacc7a3d11 (patch)
treef0b215577427ab12ab4ae7b3f45cd6ad3fe16499 /include/linux/list_nulls.h
parente8b2dfe9b4501ed0047459b2756ba26e5a940a69 (diff)
rcu: Introduce hlist_nulls variant of hlist
hlist uses NULL value to finish a chain. hlist_nulls variant use the low order bit set to 1 to signal an end-of-list marker. This allows to store many different end markers, so that some RCU lockless algos (used in TCP/UDP stack for example) can save some memory barriers in fast paths. Two new files are added : include/linux/list_nulls.h - mimics hlist part of include/linux/list.h, derived to hlist_nulls variant include/linux/rculist_nulls.h - mimics hlist part of include/linux/rculist.h, derived to hlist_nulls variant Only four helpers are declared for the moment : hlist_nulls_del_init_rcu(), hlist_nulls_del_rcu(), hlist_nulls_add_head_rcu() and hlist_nulls_for_each_entry_rcu() prefetches() were removed, since an end of list is not anymore NULL value. prefetches() could trigger useless (and possibly dangerous) memory transactions. Example of use (extracted from __udp4_lib_lookup()) struct sock *sk, *result; struct hlist_nulls_node *node; unsigned short hnum = ntohs(dport); unsigned int hash = udp_hashfn(net, hnum); struct udp_hslot *hslot = &udptable->hash[hash]; int score, badness; rcu_read_lock(); begin: result = NULL; badness = -1; sk_nulls_for_each_rcu(sk, node, &hslot->head) { score = compute_score(sk, net, saddr, hnum, sport, daddr, dport, dif); if (score > badness) { result = sk; badness = score; } } /* * if the nulls value we got at the end of this lookup is * not the expected one, we must restart lookup. * We probably met an item that was moved to another chain. */ if (get_nulls_value(node) != hash) goto begin; if (result) { if (unlikely(!atomic_inc_not_zero(&result->sk_refcnt))) result = NULL; else if (unlikely(compute_score(result, net, saddr, hnum, sport, daddr, dport, dif) < badness)) { sock_put(result); goto begin; } } rcu_read_unlock(); return result; Signed-off-by: Eric Dumazet <dada1@cosmosbay.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/list_nulls.h')
-rw-r--r--include/linux/list_nulls.h94
1 files changed, 94 insertions, 0 deletions
diff --git a/include/linux/list_nulls.h b/include/linux/list_nulls.h
new file mode 100644
index 000000000000..93150ecf3ea4
--- /dev/null
+++ b/include/linux/list_nulls.h
@@ -0,0 +1,94 @@
+#ifndef _LINUX_LIST_NULLS_H
+#define _LINUX_LIST_NULLS_H
+
+/*
+ * Special version of lists, where end of list is not a NULL pointer,
+ * but a 'nulls' marker, which can have many different values.
+ * (up to 2^31 different values guaranteed on all platforms)
+ *
+ * In the standard hlist, termination of a list is the NULL pointer.
+ * In this special 'nulls' variant, we use the fact that objects stored in
+ * a list are aligned on a word (4 or 8 bytes alignment).
+ * We therefore use the last significant bit of 'ptr' :
+ * Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
+ * Set to 0 : This is a pointer to some object (ptr)
+ */
+
+struct hlist_nulls_head {
+ struct hlist_nulls_node *first;
+};
+
+struct hlist_nulls_node {
+ struct hlist_nulls_node *next, **pprev;
+};
+#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
+ ((ptr)->first = (struct hlist_nulls_node *) (1UL | (((long)nulls) << 1)))
+
+#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
+/**
+ * ptr_is_a_nulls - Test if a ptr is a nulls
+ * @ptr: ptr to be tested
+ *
+ */
+static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
+{
+ return ((unsigned long)ptr & 1);
+}
+
+/**
+ * get_nulls_value - Get the 'nulls' value of the end of chain
+ * @ptr: end of chain
+ *
+ * Should be called only if is_a_nulls(ptr);
+ */
+static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
+{
+ return ((unsigned long)ptr) >> 1;
+}
+
+static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
+{
+ return !h->pprev;
+}
+
+static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
+{
+ return is_a_nulls(h->first);
+}
+
+static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
+{
+ struct hlist_nulls_node *next = n->next;
+ struct hlist_nulls_node **pprev = n->pprev;
+ *pprev = next;
+ if (!is_a_nulls(next))
+ next->pprev = pprev;
+}
+
+/**
+ * hlist_nulls_for_each_entry - iterate over list of given type
+ * @tpos: the type * to use as a loop cursor.
+ * @pos: the &struct hlist_node to use as a loop cursor.
+ * @head: the head for your list.
+ * @member: the name of the hlist_node within the struct.
+ *
+ */
+#define hlist_nulls_for_each_entry(tpos, pos, head, member) \
+ for (pos = (head)->first; \
+ (!is_a_nulls(pos)) && \
+ ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
+ pos = pos->next)
+
+/**
+ * hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
+ * @tpos: the type * to use as a loop cursor.
+ * @pos: the &struct hlist_node to use as a loop cursor.
+ * @member: the name of the hlist_node within the struct.
+ *
+ */
+#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
+ for (; (!is_a_nulls(pos)) && \
+ ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
+ pos = pos->next)
+
+#endif