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inetpeer: remove unused list

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Andi Kleen and Tim Chen reported huge contention on inetpeer
unused_peers.lock, on memcached workload on a 40 core machine, with
disabled route cache.

It appears we constantly flip peers refcnt between 0 and 1 values, and
we must insert/remove peers from unused_peers.list, holding a contended
spinlock.

Remove this list completely and perform a garbage collection on-the-fly,
at lookup time, using the expired nodes we met during the tree
traversal.

This removes a lot of code, makes locking more standard, and obsoletes
two sysctls (inet_peer_gc_mintime and inet_peer_gc_maxtime). This also
removes two pointers in inet_peer structure.

There is still a false sharing effect because refcnt is in first cache
line of object [were the links and keys used by lookups are located], we
might move it at the end of inet_peer structure to let this first cache
line mostly read by cpus.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Andi Kleen <andi@firstfloor.org>
CC: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2011-06-08 13:35:34 +00:00 committed by David S. Miller
parent 9ad7c049f0
commit 4b9d9be839
5 changed files with 73 additions and 233 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

10
Documentation/networking/ip-sysctl.txt
View file

@ -106,16 +106,6 @@ inet_peer_maxttl - INTEGER
when the number of entries in the pool is very small).
Measured in seconds.
inet_peer_gc_mintime - INTEGER
Minimum interval between garbage collection passes. This interval is
in effect under high memory pressure on the pool.
Measured in seconds.
inet_peer_gc_maxtime - INTEGER
Minimum interval between garbage collection passes. This interval is
in effect under low (or absent) memory pressure on the pool.
Measured in seconds.
TCP variables:
somaxconn - INTEGER

2
include/net/inetpeer.h
View file

@ -32,7 +32,6 @@ struct inet_peer {
struct inet_peer __rcu *avl_left, *avl_right;
struct inetpeer_addr daddr;
__u32 avl_height;
struct list_head unused;
__u32 dtime; /* the time of last use of not
* referenced entries */
atomic_t refcnt;
@ -56,6 +55,7 @@ struct inet_peer {
struct inetpeer_addr_base redirect_learned;
};
struct rcu_head rcu;
struct inet_peer *gc_next;
};
};

2
include/net/ip.h
View file

@ -228,8 +228,6 @@ extern struct ctl_path net_ipv4_ctl_path[];
extern int inet_peer_threshold;
extern int inet_peer_minttl;
extern int inet_peer_maxttl;
extern int inet_peer_gc_mintime;
extern int inet_peer_gc_maxtime;
/* From ip_output.c */
extern int sysctl_ip_dynaddr;

278
net/ipv4/inetpeer.c
View file

@ -54,15 +54,11 @@
* 1. Nodes may appear in the tree only with the pool lock held.
* 2. Nodes may disappear from the tree only with the pool lock held
* AND reference count being 0.
* 3. Nodes appears and disappears from unused node list only under
* "inet_peer_unused_lock".
* 4. Global variable peer_total is modified under the pool lock.
* 5. struct inet_peer fields modification:
* 3. Global variable peer_total is modified under the pool lock.
* 4. struct inet_peer fields modification:
* avl_left, avl_right, avl_parent, avl_height: pool lock
* unused: unused node list lock
* refcnt: atomically against modifications on other CPU;
* usually under some other lock to prevent node disappearing
* dtime: unused node list lock
* daddr: unchangeable
* ip_id_count: atomic value (no lock needed)
*/
@ -104,19 +100,6 @@ int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries m
* aggressively at this stage */
int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
int inet_peer_gc_mintime __read_mostly = 10 * HZ;
int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
static struct {
struct list_head list;
spinlock_t lock;
} unused_peers = {
.list = LIST_HEAD_INIT(unused_peers.list),
.lock = __SPIN_LOCK_UNLOCKED(unused_peers.lock),
};
static void peer_check_expire(unsigned long dummy);
static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
/* Called from ip_output.c:ip_init */
@ -142,21 +125,6 @@ void __init inet_initpeers(void)
0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
NULL);
/* All the timers, started at system startup tend
to synchronize. Perturb it a bit.
*/
peer_periodic_timer.expires = jiffies
+ net_random() % inet_peer_gc_maxtime
+ inet_peer_gc_maxtime;
add_timer(&peer_periodic_timer);
}
/* Called with or without local BH being disabled. */
static void unlink_from_unused(struct inet_peer *p)
{
spin_lock_bh(&unused_peers.lock);
list_del_init(&p->unused);
spin_unlock_bh(&unused_peers.lock);
}
static int addr_compare(const struct inetpeer_addr *a,
@ -203,20 +171,6 @@ static int addr_compare(const struct inetpeer_addr *a,
u; \
})
static bool atomic_add_unless_return(atomic_t *ptr, int a, int u, int *newv)
{
int cur, old = atomic_read(ptr);
while (old != u) {
*newv = old + a;
cur = atomic_cmpxchg(ptr, old, *newv);
if (cur == old)
return true;
old = cur;
}
return false;
}
/*
* Called with rcu_read_lock()
* Because we hold no lock against a writer, its quite possible we fall
@ -225,8 +179,7 @@ static bool atomic_add_unless_return(atomic_t *ptr, int a, int u, int *newv)
* We exit from this function if number of links exceeds PEER_MAXDEPTH
*/
static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
struct inet_peer_base *base,
int *newrefcnt)
struct inet_peer_base *base)
{
struct inet_peer *u = rcu_dereference(base->root);
int count = 0;
@ -235,11 +188,9 @@ static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
int cmp = addr_compare(daddr, &u->daddr);
if (cmp == 0) {
/* Before taking a reference, check if this entry was
* deleted, unlink_from_pool() sets refcnt=-1 to make
* distinction between an unused entry (refcnt=0) and
* a freed one.
* deleted (refcnt=-1)
*/
if (!atomic_add_unless_return(&u->refcnt, 1, -1, newrefcnt))
if (!atomic_add_unless(&u->refcnt, 1, -1))
u = NULL;
return u;
}
@ -366,137 +317,96 @@ static void inetpeer_free_rcu(struct rcu_head *head)
kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
}
/* May be called with local BH enabled. */
static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
struct inet_peer __rcu **stack[PEER_MAXDEPTH])
{
int do_free;
struct inet_peer __rcu ***stackptr, ***delp;
do_free = 0;
write_seqlock_bh(&base->lock);
/* Check the reference counter. It was artificially incremented by 1
* in cleanup() function to prevent sudden disappearing. If we can
* atomically (because of lockless readers) take this last reference,
* it's safe to remove the node and free it later.
* We use refcnt=-1 to alert lockless readers this entry is deleted.
*/
if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) {
struct inet_peer __rcu ***stackptr, ***delp;
if (lookup(&p->daddr, stack, base) != p)
BUG();
delp = stackptr - 1; /* *delp[0] == p */
if (p->avl_left == peer_avl_empty_rcu) {
*delp[0] = p->avl_right;
--stackptr;
} else {
/* look for a node to insert instead of p */
struct inet_peer *t;
t = lookup_rightempty(p, base);
BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
**--stackptr = t->avl_left;
/* t is removed, t->daddr > x->daddr for any
* x in p->avl_left subtree.
* Put t in the old place of p. */
RCU_INIT_POINTER(*delp[0], t);
t->avl_left = p->avl_left;
t->avl_right = p->avl_right;
t->avl_height = p->avl_height;
BUG_ON(delp[1] != &p->avl_left);
delp[1] = &t->avl_left; /* was &p->avl_left */
}
peer_avl_rebalance(stack, stackptr, base);
base->total--;
do_free = 1;
if (lookup(&p->daddr, stack, base) != p)
BUG();
delp = stackptr - 1; /* *delp[0] == p */
if (p->avl_left == peer_avl_empty_rcu) {
*delp[0] = p->avl_right;
--stackptr;
} else {
/* look for a node to insert instead of p */
struct inet_peer *t;
t = lookup_rightempty(p, base);
BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
**--stackptr = t->avl_left;
/* t is removed, t->daddr > x->daddr for any
* x in p->avl_left subtree.
* Put t in the old place of p. */
RCU_INIT_POINTER(*delp[0], t);
t->avl_left = p->avl_left;
t->avl_right = p->avl_right;
t->avl_height = p->avl_height;
BUG_ON(delp[1] != &p->avl_left);
delp[1] = &t->avl_left; /* was &p->avl_left */
}
write_sequnlock_bh(&base->lock);
if (do_free)
call_rcu(&p->rcu, inetpeer_free_rcu);
else
/* The node is used again. Decrease the reference counter
* back. The loop "cleanup -> unlink_from_unused
* -> unlink_from_pool -> putpeer -> link_to_unused
* -> cleanup (for the same node)"
* doesn't really exist because the entry will have a
* recent deletion time and will not be cleaned again soon.
*/
inet_putpeer(p);
peer_avl_rebalance(stack, stackptr, base);
base->total--;
call_rcu(&p->rcu, inetpeer_free_rcu);
}
static struct inet_peer_base *family_to_base(int family)
{
return (family == AF_INET ? &v4_peers : &v6_peers);
return family == AF_INET ? &v4_peers : &v6_peers;
}
static struct inet_peer_base *peer_to_base(struct inet_peer *p)
/* perform garbage collect on all items stacked during a lookup */
static int inet_peer_gc(struct inet_peer_base *base,
struct inet_peer __rcu **stack[PEER_MAXDEPTH],
struct inet_peer __rcu ***stackptr)
{
return family_to_base(p->daddr.family);
}
struct inet_peer *p, *gchead = NULL;
__u32 delta, ttl;
int cnt = 0;
/* May be called with local BH enabled. */
static int cleanup_once(unsigned long ttl, struct inet_peer __rcu **stack[PEER_MAXDEPTH])
{
struct inet_peer *p = NULL;
/* Remove the first entry from the list of unused nodes. */
spin_lock_bh(&unused_peers.lock);
if (!list_empty(&unused_peers.list)) {
__u32 delta;
p = list_first_entry(&unused_peers.list, struct inet_peer, unused);
if (base->total >= inet_peer_threshold)
ttl = 0; /* be aggressive */
else
ttl = inet_peer_maxttl
- (inet_peer_maxttl - inet_peer_minttl) / HZ *
base->total / inet_peer_threshold * HZ;
stackptr--; /* last stack slot is peer_avl_empty */
while (stackptr > stack) {
stackptr--;
p = rcu_deref_locked(**stackptr, base);
delta = (__u32)jiffies - p->dtime;
if (delta < ttl) {
/* Do not prune fresh entries. */
spin_unlock_bh(&unused_peers.lock);
return -1;
if (atomic_read(&p->refcnt) == 0 && delta >= ttl &&
atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
p->gc_next = gchead;
gchead = p;
}
list_del_init(&p->unused);
/* Grab an extra reference to prevent node disappearing
* before unlink_from_pool() call. */
atomic_inc(&p->refcnt);
}
spin_unlock_bh(&unused_peers.lock);
if (p == NULL)
/* It means that the total number of USED entries has
* grown over inet_peer_threshold. It shouldn't really
* happen because of entry limits in route cache. */
return -1;
unlink_from_pool(p, peer_to_base(p), stack);
return 0;
while ((p = gchead) != NULL) {
gchead = p->gc_next;
cnt++;
unlink_from_pool(p, base, stack);
}
return cnt;
}
/* Called with or without local BH being disabled. */
struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
{
struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
struct inet_peer_base *base = family_to_base(daddr->family);
struct inet_peer *p;
unsigned int sequence;
int invalidated, newrefcnt = 0;
int invalidated, gccnt = 0;
/* Look up for the address quickly, lockless.
/* Attempt a lockless lookup first.
* Because of a concurrent writer, we might not find an existing entry.
*/
rcu_read_lock();
sequence = read_seqbegin(&base->lock);
p = lookup_rcu(daddr, base, &newrefcnt);
p = lookup_rcu(daddr, base);
invalidated = read_seqretry(&base->lock, sequence);
rcu_read_unlock();
if (p) {
found: /* The existing node has been found.
* Remove the entry from unused list if it was there.
*/
if (newrefcnt == 1)
unlink_from_unused(p);
if (p)
return p;
}
/* If no writer did a change during our lookup, we can return early. */
if (!create && !invalidated)
@ -506,11 +416,17 @@ struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
* At least, nodes should be hot in our cache.
*/
write_seqlock_bh(&base->lock);
relookup:
p = lookup(daddr, stack, base);
if (p != peer_avl_empty) {
newrefcnt = atomic_inc_return(&p->refcnt);
atomic_inc(&p->refcnt);
write_sequnlock_bh(&base->lock);
goto found;
return p;
}
if (!gccnt) {
gccnt = inet_peer_gc(base, stack, stackptr);
if (gccnt && create)
goto relookup;
}
p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
if (p) {
@ -525,7 +441,6 @@ struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
p->pmtu_expires = 0;
p->pmtu_orig = 0;
memset(&p->redirect_learned, 0, sizeof(p->redirect_learned));
INIT_LIST_HEAD(&p->unused);
/* Link the node. */
@ -534,63 +449,14 @@ struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
}
write_sequnlock_bh(&base->lock);
if (base->total >= inet_peer_threshold)
/* Remove one less-recently-used entry. */
cleanup_once(0, stack);
return p;
}
static int compute_total(void)
{
return v4_peers.total + v6_peers.total;
}
EXPORT_SYMBOL_GPL(inet_getpeer);
/* Called with local BH disabled. */
static void peer_check_expire(unsigned long dummy)
{
unsigned long now = jiffies;
int ttl, total;
struct inet_peer __rcu **stack[PEER_MAXDEPTH];
total = compute_total();
if (total >= inet_peer_threshold)
ttl = inet_peer_minttl;
else
ttl = inet_peer_maxttl
- (inet_peer_maxttl - inet_peer_minttl) / HZ *
total / inet_peer_threshold * HZ;
while (!cleanup_once(ttl, stack)) {
if (jiffies != now)
break;
}
/* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
* interval depending on the total number of entries (more entries,
* less interval). */
total = compute_total();
if (total >= inet_peer_threshold)
peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
else
peer_periodic_timer.expires = jiffies
+ inet_peer_gc_maxtime
- (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
total / inet_peer_threshold * HZ;
add_timer(&peer_periodic_timer);
}
void inet_putpeer(struct inet_peer *p)
{
local_bh_disable();
if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) {
list_add_tail(&p->unused, &unused_peers.list);
p->dtime = (__u32)jiffies;
spin_unlock(&unused_peers.lock);
}
local_bh_enable();
p->dtime = (__u32)jiffies;
atomic_dec(&p->refcnt);
}
EXPORT_SYMBOL_GPL(inet_putpeer);

14
net/ipv4/sysctl_net_ipv4.c
View file

@ -397,20 +397,6 @@ static struct ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec_jiffies,
},
{
.procname = "inet_peer_gc_mintime",
.data = &inet_peer_gc_mintime,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_jiffies,
},
{
.procname = "inet_peer_gc_maxtime",
.data = &inet_peer_gc_maxtime,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_jiffies,
},
{
.procname = "tcp_orphan_retries",
.data = &sysctl_tcp_orphan_retries,