Re: [PATCH -mm 0/3] sysv ipc: increase msgmnb with the number of cpus

Solofo.Ramangalahy
2008-07-03T07:12:34Z

Andrew Morton writes:
> I'm afraid I've lost track of what's happening here. Did we come up
> with an alternative to "magical positive-versus-negative number trick"?

Yes, several proposals:
1. /proc/sys/kernel/automatic-msgmnb
(attempt attached).

2. a variation /sys/kernel/automatic/msgmn*
as a mean to alleviate the doubling of the interface.

> Your patch #1 adds and uses recompute_msgmnb() without adding the
> declaration to a header file. Your patch #2 does add the
> recompute_msgmnb() to a header file, so we have a window in which the
> build is broken, which is bad.

Sorry. Another fix needed to my quilt workflow.
Thanks.

> recompute_msgmnb() isn't a terribly good globally-visible identifier,
> btw. It is nice to add some subsystem identifer as a prefix. There's
> little chance of this symbol colliding with anything else, so this is a
> minor cosmetic thing in this case.

ok. msg_recompute_msgmnb seems to be the better name.

--
solofo

Index: b/ipc/msg.c
===================================================================
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -38,6 +38,7 @@
#include <linux/rwsem.h>
#include <linux/nsproxy.h>
#include <linux/ipc_namespace.h>
+#include <linux/cpumask.h>

#include <asm/current.h>
#include <asm/uaccess.h>
@@ -90,9 +91,11 @@ void recompute_msgmni(struct ipc_namespa
unsigned long allowed;
int nb_ns;

+ if (!ns->msg_ctlmni_activated)
+ return;
si_meminfo(&i);
allowed = (((i.totalram - i.totalhigh) / MSG_MEM_SCALE) * i.mem_unit)
- / MSGMNB;
+ / ns->msg_ctlmnb;
nb_ns = atomic_read(&nr_ipc_ns);
allowed /= nb_ns;

@@ -108,11 +111,23 @@ void recompute_msgmni(struct ipc_namespa

ns->msg_ctlmni = allowed;
}
+/*
+ * Scale msgmnb with the number of online cpus, up to 4x MSGMNB.
+ */
+void msg_recompute_msgmnb(struct ipc_namespace *ns)
+{
+ if (!ns->msg_ctlmnb_activated)
+ return;
+ ns->msg_ctlmnb =
+ min(MSGMNB * num_online_cpus(), MSGMNB * MSG_CPU_SCALE);
+}

void msg_init_ns(struct ipc_namespace *ns)
{
ns->msg_ctlmax = MSGMAX;
- ns->msg_ctlmnb = MSGMNB;
+ ns->msg_ctlmnb_activated = 1;
+ ns->msg_ctlmni_activated = 1;
+ msg_recompute_msgmnb(ns);

recompute_msgmni(ns);

@@ -132,8 +147,8 @@ void __init msg_init(void)
{
msg_init_ns(&init_ipc_ns);

- printk(KERN_INFO "msgmni has been set to %d\n",
- init_ipc_ns.msg_ctlmni);
+ printk(KERN_INFO "msgmni has been set to %d, msgmnb to %d\n",
+ init_ipc_ns.msg_ctlmni, init_ipc_ns.msg_ctlmnb);

ipc_init_proc_interface("sysvipc/msg",
" key msqid perms cbytes qnum lspid lrpid uid gid cuid cgid stime rtime ctime\n",
Index: b/include/linux/msg.h
===================================================================
--- a/include/linux/msg.h
+++ b/include/linux/msg.h
@@ -58,6 +58,12 @@ struct msginfo {
* more than 16 GB : msgmni = 32K (IPCMNI)
*/
#define MSG_MEM_SCALE 32
+/*
+ * Scaling factor to compute msgmnb: ns->msg_ctlmnb is between MSGMNB
+ * and MSGMNB * MSG_CPU_SCALE. This leads to a max msgmnb value of
+ * 65536 which is an already used and recommended value.
+ */
+#define MSG_CPU_SCALE 4

#define MSGMNI 16 /* <= IPCMNI */ /* max # of msg queue identifiers */
#define MSGMAX 8192 /* <= INT_MAX */ /* max size of message (bytes) */
Index: b/ipc/ipc_sysctl.c
===================================================================
--- a/ipc/ipc_sysctl.c
+++ b/ipc/ipc_sysctl.c
@@ -31,19 +31,22 @@ static void *get_ipc(ctl_table *table)
* hand and it has a callback routine registered on the ipc namespace notifier
* chain: we don't want such tunables to be recomputed anymore upon memory
* add/remove or ipc namespace creation/removal.
- * They can come back to a recomputable state by being set to a <0 value.
*/
-static void tunable_set_callback(int val)
+static void tunable_set_callback(int val, ctl_table *table)
{
- if (val >= 0)
- unregister_ipcns_notifier(current->nsproxy->ipc_ns);
- else {
- /*
- * Re-enable automatic recomputing only if not already
- * enabled.
- */
- recompute_msgmni(current->nsproxy->ipc_ns);
- cond_register_ipcns_notifier(current->nsproxy->ipc_ns);
+ int tunable = table->ctl_name;
+
+ switch (tunable) {
+ case KERN_MSGMNB:
+ current->nsproxy->ipc_ns->msg_ctlmnb_activated = 0;
+ break;
+ case KERN_MSGMNI:
+ current->nsproxy->ipc_ns->msg_ctlmni_activated = 0;
+ break;
+ default:
+ printk(KERN_ERR "ipc: unexpected value %s\n",
+ table->procname);
+ break;
}
}

@@ -70,9 +73,10 @@ static int proc_ipc_callback_dointvec(ct

rc = proc_dointvec(&ipc_table, write, filp, buffer, lenp, ppos);

- if (write && !rc && lenp_bef == *lenp)
- tunable_set_callback(*((int *)(ipc_table.data)));
-
+ if (write && !rc && lenp_bef == *lenp) {
+ BUG_ON(table == NULL);
+ tunable_set_callback(*((int *)(ipc_table.data)), table);
+ }
return rc;
}

@@ -147,8 +151,8 @@ static int sysctl_ipc_registered_data(ct
* Tunable has successfully been changed from userland
*/
int *data = get_ipc(table);
-
- tunable_set_callback(*data);
+ BUG_ON(table == NULL);
+ tunable_set_callback(*data, table);
}

return rc;
@@ -210,6 +214,15 @@ static struct ctl_table ipc_kern_table[]
.data = &init_ipc_ns.msg_ctlmnb,
.maxlen = sizeof (init_ipc_ns.msg_ctlmnb),
.mode = 0644,
+ .proc_handler = proc_ipc_callback_dointvec,
+ .strategy = sysctl_ipc_registered_data,
+ },
+ {
+ .ctl_name = KERN_AUTOMATIC_MSGMNB,
+ .procname = "automatic_msgmnb",
+ .data = &init_ipc_ns.msg_ctlmnb_activated,
+ .maxlen = sizeof (init_ipc_ns.msg_ctlmnb_activated),
+ .mode = 0644,
.proc_handler = proc_ipc_dointvec,
.strategy = sysctl_ipc_data,
},
Index: b/include/linux/ipc_namespace.h
===================================================================
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -12,6 +12,7 @@
#define IPCNS_MEMCHANGED 0x00000001 /* Notify lowmem size changed */
#define IPCNS_CREATED 0x00000002 /* Notify new ipc namespace created */
#define IPCNS_REMOVED 0x00000003 /* Notify ipc namespace removed */
+#define IPCNS_CPUCHANGED 0x00000004 /* Notify cpu hotplug addition/removal */

#define IPCNS_CALLBACK_PRI 0

@@ -33,7 +34,9 @@ struct ipc_namespace {

int msg_ctlmax;
int msg_ctlmnb;
+ int msg_ctlmnb_activated;
int msg_ctlmni;
+ int msg_ctlmni_activated;
atomic_t msg_bytes;
atomic_t msg_hdrs;

@@ -52,7 +55,6 @@ extern atomic_t nr_ipc_ns;
#define INIT_IPC_NS(ns) .ns = &init_ipc_ns,

extern int register_ipcns_notifier(struct ipc_namespace *);
-extern int cond_register_ipcns_notifier(struct ipc_namespace *);
extern int unregister_ipcns_notifier(struct ipc_namespace *);
extern int ipcns_notify(unsigned long);

Index: b/ipc/util.c
===================================================================
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -34,6 +34,7 @@
#include <linux/nsproxy.h>
#include <linux/rwsem.h>
#include <linux/memory.h>
+#include <linux/cpu.h>
#include <linux/ipc_namespace.h>

#include <asm/unistd.h>
@@ -96,6 +97,32 @@ static int ipc_memory_callback(struct no

#endif /* CONFIG_MEMORY_HOTPLUG */

+#ifdef CONFIG_HOTPLUG_CPU
+
+static void ipc_cpu_notifier(struct work_struct *work)
+{
+ ipcns_notify(IPCNS_CPUCHANGED);
+}
+
+static DECLARE_WORK(ipc_cpu_wq, ipc_cpu_notifier);
+
+static int __cpuinit ipc_cpu_callback(struct notifier_block *nfb,
+ unsigned long action, void *hcpu)
+{
+ switch (action) {
+ case CPU_ONLINE:
+ case CPU_ONLINE_FROZEN:
+ case CPU_DEAD:
+ case CPU_DEAD_FROZEN:
+ schedule_work(&ipc_cpu_wq);
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+#endif /* CONFIG_HOTPLUG_CPU */
/**
* ipc_init - initialise IPC subsystem
*
@@ -112,6 +139,7 @@ static int __init ipc_init(void)
msg_init();
shm_init();
hotplug_memory_notifier(ipc_memory_callback, IPC_CALLBACK_PRI);
+ hotcpu_notifier(ipc_cpu_callback, IPC_CALLBACK_PRI);
register_ipcns_notifier(&init_ipc_ns);
return 0;
}
Index: b/ipc/ipcns_notifier.c
===================================================================
--- a/ipc/ipcns_notifier.c
+++ b/ipc/ipcns_notifier.c
@@ -26,16 +26,20 @@ static int ipcns_callback(struct notifie
unsigned long action, void *arg)
{
struct ipc_namespace *ns;
-
+ ns = container_of(self, struct ipc_namespace, ipcns_nb);
switch (action) {
+ case IPCNS_CPUCHANGED:
+ /*
+ * Fall through.
+ * We do not scale msgmnb with IPC namespace
+ * add/remove for simplicity (adjustment of the
+ * message pool is done indirectly via msgmni).
+ */
+ msg_recompute_msgmnb(ns);
case IPCNS_MEMCHANGED: /* amount of lowmem has changed */
case IPCNS_CREATED:
case IPCNS_REMOVED:
/*
- * It's time to recompute msgmni
- */
- ns = container_of(self, struct ipc_namespace, ipcns_nb);
- /*
* No need to get a reference on the ns: the 1st job of
* free_ipc_ns() is to unregister the callback routine.
* blocking_notifier_chain_unregister takes the wr lock to do
@@ -61,15 +65,6 @@ int register_ipcns_notifier(struct ipc_n
return blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
}

-int cond_register_ipcns_notifier(struct ipc_namespace *ns)
-{
- memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
- ns->ipcns_nb.notifier_call = ipcns_callback;
- ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
- return blocking_notifier_chain_cond_register(&ipcns_chain,
- &ns->ipcns_nb);
-}
-
int unregister_ipcns_notifier(struct ipc_namespace *ns)
{
return blocking_notifier_chain_unregister(&ipcns_chain,
Index: b/ipc/util.h
===================================================================
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -122,6 +122,7 @@ extern struct msg_msg *load_msg(const vo
extern int store_msg(void __user *dest, struct msg_msg *msg, int len);

extern void recompute_msgmni(struct ipc_namespace *);
+extern void msg_recompute_msgmnb(struct ipc_namespace *);

static inline int ipc_buildid(int id, int seq)
{
Index: b/include/linux/sysctl.h
===================================================================
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -163,6 +163,7 @@ enum
KERN_MAX_LOCK_DEPTH=74,
KERN_NMI_WATCHDOG=75, /* int: enable/disable nmi watchdog */
KERN_PANIC_ON_NMI=76, /* int: whether we will panic on an unrecovered */
+ KERN_AUTOMATIC_MSGMNB=77, /* int: automatic msgmnb computation */
};

Index: b/kernel/sysctl_check.c
===================================================================
--- a/kernel/sysctl_check.c
+++ b/kernel/sysctl_check.c
@@ -104,6 +104,7 @@ static const struct trans_ctl_table tran
{ KERN_MAX_LOCK_DEPTH, "max_lock_depth" },
{ KERN_NMI_WATCHDOG, "nmi_watchdog" },
{ KERN_PANIC_ON_NMI, "panic_on_unrecovered_nmi" },
+ { KERN_AUTOMATIC_MSGMNB, "automatic_msgmnb" },
{}
};