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ipc: do not use a negative value to re-enable msgmni automatic recomp…

…uting

This patch proposes an alternative to the "magical
positive-versus-negative number trick" Andrew complained about last week
in http://lkml.org/lkml/2008/6/24/418.

This had been introduced with the patches that scale msgmni to the amount
of lowmem.  With these patches, msgmni has a registered notification
routine that recomputes msgmni value upon memory add/remove or ipc
namespace creation/ removal.

When msgmni is changed from user space (i.e.  value written to the proc
file), that notification routine is unregistered, and the way to make it
registered back is to write a negative value into the proc file.  This is
the "magical positive-versus-negative number trick".

To fix this, a new proc file is introduced: /proc/sys/kernel/auto_msgmni.
This file acts as ON/OFF for msgmni automatic recomputing.

With this patch, the process is the following:
1) kernel boots in "automatic recomputing mode"
   /proc/sys/kernel/msgmni contains the value that has been computed (depends
                           on lowmem)
   /proc/sys/kernel/automatic_msgmni contains "1"

2) echo <val> > /proc/sys/kernel/msgmni
   . sets msg_ctlmni to <val>
   . de-activates automatic recomputing (i.e. if, say, some memory is added
     msgmni won't be recomputed anymore)
   . /proc/sys/kernel/automatic_msgmni now contains "0"

3) echo "0" > /proc/sys/kernel/automatic_msgmni
   . de-activates msgmni automatic recomputing
     this has the same effect as 2) except that msg_ctlmni's value stays
     blocked at its current value)

3) echo "1" > /proc/sys/kernel/automatic_msgmni
   . recomputes msgmni's value based on the current available memory size
     and number of ipc namespaces
   . re-activates automatic recomputing for msgmni.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Solofo Ramangalahy <Solofo.Ramangalahy@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1 parent f1a43f9 commit 9eefe520c814f6f62c5d36a2ddcd3fb99dfdb30e Nadia Derbey committed with Jul 25, 2008
Showing with 76 additions and 19 deletions.
  1. +2 −1 include/linux/ipc_namespace.h
  2. +59 −13 ipc/ipc_sysctl.c
  3. +15 −5 ipc/ipcns_notifier.c
View
3 include/linux/ipc_namespace.h
@@ -36,6 +36,7 @@ struct ipc_namespace {
int msg_ctlmni;
atomic_t msg_bytes;
atomic_t msg_hdrs;
+ int auto_msgmni;
size_t shm_ctlmax;
size_t shm_ctlall;
@@ -53,7 +54,7 @@ extern atomic_t nr_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 void unregister_ipcns_notifier(struct ipc_namespace *);
extern int ipcns_notify(unsigned long);
#else /* CONFIG_SYSVIPC */
View
72 ipc/ipc_sysctl.c
@@ -27,15 +27,17 @@ static void *get_ipc(ctl_table *table)
}
/*
- * Routine that is called when a tunable has successfully been changed by
- * 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.
+ * Routine that is called when the file "auto_msgmni" has successfully been
+ * written.
+ * Two values are allowed:
+ * 0: unregister msgmni's callback routine from the ipc namespace notifier
+ * chain. This means that msgmni won't be recomputed anymore upon memory
+ * add/remove or ipc namespace creation/removal.
+ * 1: register back the callback routine.
*/
-static void tunable_set_callback(int val)
+static void ipc_auto_callback(int val)
{
- if (val >= 0)
+ if (!val)
unregister_ipcns_notifier(current->nsproxy->ipc_ns);
else {
/*
@@ -71,7 +73,12 @@ static int proc_ipc_callback_dointvec(ctl_table *table, int write,
rc = proc_dointvec(&ipc_table, write, filp, buffer, lenp, ppos);
if (write && !rc && lenp_bef == *lenp)
- tunable_set_callback(*((int *)(ipc_table.data)));
+ /*
+ * Tunable has successfully been changed by hand. Disable its
+ * automatic adjustment. This simply requires unregistering
+ * the notifiers that trigger recalculation.
+ */
+ unregister_ipcns_notifier(current->nsproxy->ipc_ns);
return rc;
}
@@ -87,10 +94,39 @@ static int proc_ipc_doulongvec_minmax(ctl_table *table, int write,
lenp, ppos);
}
+static int proc_ipcauto_dointvec_minmax(ctl_table *table, int write,
+ struct file *filp, void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct ctl_table ipc_table;
+ size_t lenp_bef = *lenp;
+ int oldval;
+ int rc;
+
+ memcpy(&ipc_table, table, sizeof(ipc_table));
+ ipc_table.data = get_ipc(table);
+ oldval = *((int *)(ipc_table.data));
+
+ rc = proc_dointvec_minmax(&ipc_table, write, filp, buffer, lenp, ppos);
+
+ if (write && !rc && lenp_bef == *lenp) {
+ int newval = *((int *)(ipc_table.data));
+ /*
+ * The file "auto_msgmni" has correctly been set.
+ * React by (un)registering the corresponding tunable, if the
+ * value has changed.
+ */
+ if (newval != oldval)
+ ipc_auto_callback(newval);
+ }
+
+ return rc;
+}
+
#else
#define proc_ipc_doulongvec_minmax NULL
#define proc_ipc_dointvec NULL
#define proc_ipc_callback_dointvec NULL
+#define proc_ipcauto_dointvec_minmax NULL
#endif
#ifdef CONFIG_SYSCTL_SYSCALL
@@ -142,14 +178,11 @@ static int sysctl_ipc_registered_data(ctl_table *table, int __user *name,
rc = sysctl_ipc_data(table, name, nlen, oldval, oldlenp, newval,
newlen);
- if (newval && newlen && rc > 0) {
+ if (newval && newlen && rc > 0)
/*
* Tunable has successfully been changed from userland
*/
- int *data = get_ipc(table);
-
- tunable_set_callback(*data);
- }
+ unregister_ipcns_notifier(current->nsproxy->ipc_ns);
return rc;
}
@@ -158,6 +191,9 @@ static int sysctl_ipc_registered_data(ctl_table *table, int __user *name,
#define sysctl_ipc_registered_data NULL
#endif
+static int zero;
+static int one = 1;
+
static struct ctl_table ipc_kern_table[] = {
{
.ctl_name = KERN_SHMMAX,
@@ -222,6 +258,16 @@ static struct ctl_table ipc_kern_table[] = {
.proc_handler = proc_ipc_dointvec,
.strategy = sysctl_ipc_data,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "auto_msgmni",
+ .data = &init_ipc_ns.auto_msgmni,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_ipcauto_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
{}
};
View
20 ipc/ipcns_notifier.c
@@ -55,25 +55,35 @@ static int ipcns_callback(struct notifier_block *self,
int register_ipcns_notifier(struct ipc_namespace *ns)
{
+ int rc;
+
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_register(&ipcns_chain, &ns->ipcns_nb);
+ rc = blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
+ if (!rc)
+ ns->auto_msgmni = 1;
+ return rc;
}
int cond_register_ipcns_notifier(struct ipc_namespace *ns)
{
+ int rc;
+
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,
+ rc = blocking_notifier_chain_cond_register(&ipcns_chain,
&ns->ipcns_nb);
+ if (!rc)
+ ns->auto_msgmni = 1;
+ return rc;
}
-int unregister_ipcns_notifier(struct ipc_namespace *ns)
+void unregister_ipcns_notifier(struct ipc_namespace *ns)
{
- return blocking_notifier_chain_unregister(&ipcns_chain,
- &ns->ipcns_nb);
+ blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
+ ns->auto_msgmni = 0;
}
int ipcns_notify(unsigned long val)

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