[PATCH 1/1] IPC - Do not use a negative value to re-enable msgmni automatic recomputing

[PATCH 1/1] IPC - Do not use a negative value to re-enable msgmni automatic recomputing

[Nadia.Derbey]

[-- Attachment #1: auto_msgmni_proc_file.patch --]
[-- Type: text/plain, Size: 8014 bytes --]

[PATCH 01/01]

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.

This patch applies to 2.6.26-rc5-mm3.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>

---
 include/linux/ipc_namespace.h |    1 
 ipc/ipc_sysctl.c              |   75 ++++++++++++++++++++++++++++++++++--------
 ipc/ipcns_notifier.c          |   19 ++++++++--
 3 files changed, 78 insertions(+), 17 deletions(-)

Index: linux-2.6.26-rc5-mm3/ipc/ipc_sysctl.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/ipc/ipc_sysctl.c	2008-06-16 09:12:57.000000000 +0200
+++ linux-2.6.26-rc5-mm3/ipc/ipc_sysctl.c	2008-07-03 13:29:50.000000000 +0200
@@ -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 +73,15 @@ 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)));
+		/*
+		 * Tunable has successfully been changed by hand and it has a
+		 * callback routine registered on the ipc namespace notifier
+		 * chain: we don't want this tunable to be recomputed anymore
+		 * upon memory add/remove or ipc namespace creation/removal.
+		 * It can come back to a recomputable state if the
+		 * corresponding auto_ file is set to 1.
+		 */
+		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
 
 	return rc;
 }
@@ -87,10 +97,39 @@ static int proc_ipc_doulongvec_minmax(ct
 					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 +181,11 @@ static int sysctl_ipc_registered_data(ct
 	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 +194,9 @@ static int sysctl_ipc_registered_data(ct
 #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 +261,16 @@ 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,
+	},
 	{}
 };
 
Index: linux-2.6.26-rc5-mm3/include/linux/ipc_namespace.h
===================================================================
--- linux-2.6.26-rc5-mm3.orig/include/linux/ipc_namespace.h	2008-06-16 09:12:03.000000000 +0200
+++ linux-2.6.26-rc5-mm3/include/linux/ipc_namespace.h	2008-07-03 08:33:56.000000000 +0200
@@ -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;
Index: linux-2.6.26-rc5-mm3/ipc/ipcns_notifier.c
===================================================================
--- linux-2.6.26-rc5-mm3.orig/ipc/ipcns_notifier.c	2008-06-16 09:12:57.000000000 +0200
+++ linux-2.6.26-rc5-mm3/ipc/ipcns_notifier.c	2008-07-03 11:38:07.000000000 +0200
@@ -55,25 +55,36 @@ static int ipcns_callback(struct notifie
 
 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)
 {
-	return blocking_notifier_chain_unregister(&ipcns_chain,
-						&ns->ipcns_nb);
+	blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
+	ns->auto_msgmni = 0;
+	return 0;
 }
 
 int ipcns_notify(unsigned long val)

--

Re: [PATCH 1/1] IPC - Do not use a negative value to re-enable msgmni automatic recomputing

[Matt Helsley]

On Thu, 2008-07-03 at 14:15 +0200, Nadia.Derbey@bull.net wrote:
> plain text document attachment (auto_msgmni_proc_file.patch)
> [PATCH 01/01]
> 
> 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.
> 
> This patch applies to 2.6.26-rc5-mm3.

This makes sense to me.

> Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
> 
> ---
>  include/linux/ipc_namespace.h |    1 
>  ipc/ipc_sysctl.c              |   75 ++++++++++++++++++++++++++++++++++--------
>  ipc/ipcns_notifier.c          |   19 ++++++++--
>  3 files changed, 78 insertions(+), 17 deletions(-)
> 
> Index: linux-2.6.26-rc5-mm3/ipc/ipc_sysctl.c
> ===================================================================
> --- linux-2.6.26-rc5-mm3.orig/ipc/ipc_sysctl.c	2008-06-16 09:12:57.000000000 +0200
> +++ linux-2.6.26-rc5-mm3/ipc/ipc_sysctl.c	2008-07-03 13:29:50.000000000 +0200
> @@ -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 +73,15 @@ 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)));
> +		/*
> +		 * Tunable has successfully been changed by hand and it has a
> +		 * callback routine registered on the ipc namespace notifier
> +		 * chain: we don't want this tunable to be recomputed anymore
> +		 * upon memory add/remove or ipc namespace creation/removal.
> +		 * It can come back to a recomputable state if the
> +		 * corresponding auto_ file is set to 1.
> +		 */

The register_ipcns_notifier() code tells us what will trigger the
recalculation. If that code gets changed you'd need to update this
comment. Also your comment at the top of the function describes what 0/1
mean when written to this file. So I think this comment could be greatly
simplified:

/*
 * Disabling automatic adjustment of msgmni simply requires
 * unregistering the notifiers that trigger recalculation.
 */

> +		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
> 
>  	return rc;
>  }
> @@ -87,10 +97,39 @@ static int proc_ipc_doulongvec_minmax(ct
>  					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 +181,11 @@ static int sysctl_ipc_registered_data(ct
>  	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 +194,9 @@ static int sysctl_ipc_registered_data(ct
>  #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 +261,16 @@ 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,
> +	},
>  	{}
>  };
> 
> Index: linux-2.6.26-rc5-mm3/include/linux/ipc_namespace.h
> ===================================================================
> --- linux-2.6.26-rc5-mm3.orig/include/linux/ipc_namespace.h	2008-06-16 09:12:03.000000000 +0200
> +++ linux-2.6.26-rc5-mm3/include/linux/ipc_namespace.h	2008-07-03 08:33:56.000000000 +0200
> @@ -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;
> Index: linux-2.6.26-rc5-mm3/ipc/ipcns_notifier.c
> ===================================================================
> --- linux-2.6.26-rc5-mm3.orig/ipc/ipcns_notifier.c	2008-06-16 09:12:57.000000000 +0200
> +++ linux-2.6.26-rc5-mm3/ipc/ipcns_notifier.c	2008-07-03 11:38:07.000000000 +0200
> @@ -55,25 +55,36 @@ static int ipcns_callback(struct notifie
> 
>  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)
>  {
> -	return blocking_notifier_chain_unregister(&ipcns_chain,
> -						&ns->ipcns_nb);
> +	blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
> +	ns->auto_msgmni = 0;
> +	return 0;
>  }

This looks odd -- we're no longer returning the return code from
blocking_notifier_chain_unregister(). From what I can see in the patch,
the return value is unused. Perhaps it ought to be removed? Otherwise it
might make sense to do the same as you did with "register":

        rc = blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
        if (!rc)
        	ns->auto_msgmni = 0;
        return rc;

Cheers,
	-Matt Helsley

Re: [PATCH 1/1] IPC - Do not use a negative value to re-enable msgmni automatic recomputing

[Nadia Derbey]

Matt Helsley wrote:
> On Thu, 2008-07-03 at 14:15 +0200, Nadia.Derbey@bull.net wrote:
> 
>>plain text document attachment (auto_msgmni_proc_file.patch)
>>[PATCH 01/01]
>>
>>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.
>>
>>This patch applies to 2.6.26-rc5-mm3.
> 
> 
> This makes sense to me.
> 
> 
>>Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
>>
>>---
>> include/linux/ipc_namespace.h |    1 
>> ipc/ipc_sysctl.c              |   75 ++++++++++++++++++++++++++++++++++--------
>> ipc/ipcns_notifier.c          |   19 ++++++++--
>> 3 files changed, 78 insertions(+), 17 deletions(-)
>>
>>Index: linux-2.6.26-rc5-mm3/ipc/ipc_sysctl.c
>>===================================================================
>>--- linux-2.6.26-rc5-mm3.orig/ipc/ipc_sysctl.c	2008-06-16 09:12:57.000000000 +0200
>>+++ linux-2.6.26-rc5-mm3/ipc/ipc_sysctl.c	2008-07-03 13:29:50.000000000 +0200
>>@@ -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 +73,15 @@ 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)));
>>+		/*
>>+		 * Tunable has successfully been changed by hand and it has a
>>+		 * callback routine registered on the ipc namespace notifier
>>+		 * chain: we don't want this tunable to be recomputed anymore
>>+		 * upon memory add/remove or ipc namespace creation/removal.
>>+		 * It can come back to a recomputable state if the
>>+		 * corresponding auto_ file is set to 1.
>>+		 */
> 
> 
> The register_ipcns_notifier() code tells us what will trigger the
> recalculation. If that code gets changed you'd need to update this
> comment. Also your comment at the top of the function describes what 0/1
> mean when written to this file. So I think this comment could be greatly
> simplified:
> 
> /*
>  * Disabling automatic adjustment of msgmni simply requires
>  * unregistering the notifiers that trigger recalculation.
>  */
> 
> 
>>+		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
>>
>> 	return rc;
>> }
>>@@ -87,10 +97,39 @@ static int proc_ipc_doulongvec_minmax(ct
>> 					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 +181,11 @@ static int sysctl_ipc_registered_data(ct
>> 	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 +194,9 @@ static int sysctl_ipc_registered_data(ct
>> #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 +261,16 @@ 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,
>>+	},
>> 	{}
>> };
>>
>>Index: linux-2.6.26-rc5-mm3/include/linux/ipc_namespace.h
>>===================================================================
>>--- linux-2.6.26-rc5-mm3.orig/include/linux/ipc_namespace.h	2008-06-16 09:12:03.000000000 +0200
>>+++ linux-2.6.26-rc5-mm3/include/linux/ipc_namespace.h	2008-07-03 08:33:56.000000000 +0200
>>@@ -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;
>>Index: linux-2.6.26-rc5-mm3/ipc/ipcns_notifier.c
>>===================================================================
>>--- linux-2.6.26-rc5-mm3.orig/ipc/ipcns_notifier.c	2008-06-16 09:12:57.000000000 +0200
>>+++ linux-2.6.26-rc5-mm3/ipc/ipcns_notifier.c	2008-07-03 11:38:07.000000000 +0200
>>@@ -55,25 +55,36 @@ static int ipcns_callback(struct notifie
>>
>> 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)
>> {
>>-	return blocking_notifier_chain_unregister(&ipcns_chain,
>>-						&ns->ipcns_nb);
>>+	blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
>>+	ns->auto_msgmni = 0;
>>+	return 0;
>> }
> 
> 
> This looks odd -- we're no longer returning the return code from
> blocking_notifier_chain_unregister().
> From what I can see in the patch,
> the return value is unused. Perhaps it ought to be removed? Otherwise it
> might make sense to do the same as you did with "register":
> 
>         rc = blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
>         if (!rc)
>         	ns->auto_msgmni = 0;
>         return rc;
> 
> Cheers,
> 	-Matt Helsley
> 
> 
> 

Well, I thought that the registration routines might evolve in the 
future, even though they are now unconditionally returning 0. That's why 
I'm setting the flag to 1 only if 
blocking_notifier_chain_cond_register() succeeded.
Now, talking about unregister: it acutally returns a ENOENT, but there's 
no need to test the return code, since even in that case the flag should 
be set to 0.
I'll change unregister_ipcns_notifier() into a void.

Thanks for the review, Matt!

Regards,
Nadia

[PATCH 1/1] IPC - Do not use a negative value to re-enable msgmni automatic recomputing

[Nadia.Derbey]

[-- Attachment #1: auto_msgmni_proc_file.patch --]
[-- Type: text/plain, Size: 8342 bytes --]

Resending after fixing the issues pointed out by Matt.
Now applies to 2.6.26-rc8-mm1.

[PATCH 01/01]

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.

This patch applies to 2.6.26-rc8-mm1.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>

---
 include/linux/ipc_namespace.h |    3 +
 ipc/ipc_sysctl.c              |   72 ++++++++++++++++++++++++++++++++++--------
 ipc/ipcns_notifier.c          |   20 ++++++++---
 3 files changed, 76 insertions(+), 19 deletions(-)

Index: linux-2.6.26-rc8-mm1/include/linux/ipc_namespace.h
===================================================================
--- linux-2.6.26-rc8-mm1.orig/include/linux/ipc_namespace.h	2008-07-03 16:10:39.000000000 +0200
+++ linux-2.6.26-rc8-mm1/include/linux/ipc_namespace.h	2008-07-04 08:10:50.000000000 +0200
@@ -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 */
Index: linux-2.6.26-rc8-mm1/ipc/ipcns_notifier.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/ipc/ipcns_notifier.c	2008-07-03 16:10:39.000000000 +0200
+++ linux-2.6.26-rc8-mm1/ipc/ipcns_notifier.c	2008-07-04 08:12:53.000000000 +0200
@@ -55,25 +55,35 @@ static int ipcns_callback(struct notifie
 
 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)
Index: linux-2.6.26-rc8-mm1/ipc/ipc_sysctl.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/ipc/ipc_sysctl.c	2008-07-03 16:10:39.000000000 +0200
+++ linux-2.6.26-rc8-mm1/ipc/ipc_sysctl.c	2008-07-04 08:16:36.000000000 +0200
@@ -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(ct
 	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(ct
 					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(ct
 	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(ct
 #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,
+	},
 	{}
 };
 

--

Re: [PATCH 1/1] IPC - Do not use a negative value to re-enable msgmni automatic recomputing

[Andrew Morton]

On Fri, 04 Jul 2008 08:37:16 +0200 Nadia.Derbey@bull.net wrote:

> Resending after fixing the issues pointed out by Matt.
> Now applies to 2.6.26-rc8-mm1.
> 
> [PATCH 01/01]
> 
> 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.
> 

Sigh.  I suppose it's a bit better.

> ---
>  include/linux/ipc_namespace.h |    3 +
>  ipc/ipc_sysctl.c              |   72 ++++++++++++++++++++++++++++++++++--------
>  ipc/ipcns_notifier.c          |   20 ++++++++---

Could we get this all documented for our poor users please?

Documentation/filesystems/proc.txt is probably the most appropriate
place.

Re: [PATCH 1/1] IPC - Do not use a negative value to re-enable msgmni automatic recomputing

[Nadia Derbey]

On Tue, 2008-07-22 at 03:34 -0700, Andrew Morton wrote:
> On Fri, 04 Jul 2008 08:37:16 +0200 Nadia.Derbey@bull.net wrote:
> 
> > Resending after fixing the issues pointed out by Matt.
> > Now applies to 2.6.26-rc8-mm1.
> > 
> > [PATCH 01/01]
> > 
> > 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.
> > 
> 
> Sigh.  I suppose it's a bit better.
> 
> > ---
> >  include/linux/ipc_namespace.h |    3 +
> >  ipc/ipc_sysctl.c              |   72 ++++++++++++++++++++++++++++++++++--------
> >  ipc/ipcns_notifier.c          |   20 ++++++++---
> 
> Could we get this all documented for our poor users please?
> 
> Documentation/filesystems/proc.txt is probably the most appropriate
> place.
> 
> 

Sorry for answering so late, but I just came back from a looooong
vacation.
Actually, I first thought of documenting this new file in proc.txt, but
didn't find anything related to the ipc tunables there, that's why I
finally gave up with the idea. 
I'll send an update of the proc.txt as soon as possible.

Regards,
Nadia

-- 
Nadia Derbey <Nadia.Derbey@bull.net>