Change default MSGMNI tunable to scale with system memory

[PATCH 01/02]

This patch computes msg_ctlmni to make it scale with system memory. msg_ctlmni is now set to make the message queues occupy 1/32 of the available memory.

Some cleaning has also been done in the MSGXXX constants:
. MSGPOOL: the msgctl man page says it's not used, but it also defines it as
a size in bytes (the code expresses it in Kbytes).
. MSGSEG definition has been removed since it used only once in msgctl().

===================================================================

include/linux/msg.h +3 -3

@@ -49,17 +49,17 @@ struct msginfo {
 	unsigned short  msgseg; 
 };
 
+#define MSG_MEM_SCALE 32    /* Scaling factor to compute msgmni */
+
 #define MSGMNI    16   /* <= IPCMNI */     /* max # of msg queue identifiers */
 #define MSGMAX  8192   /* <= INT_MAX */   /* max size of message (bytes) */
 #define MSGMNB 16384   /* <= INT_MAX */   /* default max size of a message queue */
 
 /* unused */
-#define MSGPOOL (MSGMNI*MSGMNB/1024)  /* size in kilobytes of message pool */
+#define MSGPOOL (MSGMNI * MSGMNB) /* size in bytes of message pool */
 #define MSGTQL  MSGMNB            /* number of system message headers */
 #define MSGMAP  MSGMNB            /* number of entries in message map */
 #define MSGSSZ  16                /* message segment size */
-#define __MSGSEG ((MSGPOOL*1024)/ MSGSSZ) /* max no. of segments */
-#define MSGSEG (__MSGSEG <= 0xffff ? __MSGSEG : 0xffff)
 
 #ifdef __KERNEL__
 #include <linux/list.h>

Index: linux-2.6.24-rc4/ipc/msg.c
===================================================================

ipc/msg.c +6 -1

@@ -27,6 +27,7 @@
 #include <linux/msg.h>
 #include <linux/spinlock.h>
 #include <linux/init.h>
+#include <linux/mm.h>
 #include <linux/proc_fs.h>
 #include <linux/list.h>
 #include <linux/security.h>

@@ -81,10 +82,25 @@ static int sysvipc_msg_proc_show(struct 
 
 static void __msg_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
 {
+	struct sysinfo i;
+	unsigned long allowed;
+
 	ns->ids[IPC_MSG_IDS] = ids;
 	ns->msg_ctlmax = MSGMAX;
 	ns->msg_ctlmnb = MSGMNB;
-	ns->msg_ctlmni = MSGMNI;
+
+	/*

Quoted 11 lines · On Tue, 11 Dec 2007 16:38:46 +0100 [email protected] wrote:

[PATCH 01/02]

This patch computes msg_ctlmni to make it scale with system memory. msg_ctlmni is now set to make the message queues occupy 1/32 of the available memory.

Some cleaning has also been done in the MSGXXX constants:
. MSGPOOL: the msgctl man page says it's not used, but it also defines it as
a size in bytes (the code expresses it in Kbytes).
. MSGSEG definition has been removed since it used only once in msgctl().

The objective seems reasonable.

Quoted 50 lines

===================================================================

include/linux/msg.h +3 -3

@@ -49,17 +49,17 @@ struct msginfo {
 	unsigned short  msgseg; 
 };
 
+#define MSG_MEM_SCALE 32    /* Scaling factor to compute msgmni */
+
 #define MSGMNI    16   /* <= IPCMNI */     /* max # of msg queue identifiers */
 #define MSGMAX  8192   /* <= INT_MAX */   /* max size of message (bytes) */
 #define MSGMNB 16384   /* <= INT_MAX */   /* default max size of a message queue */
 
 /* unused */
-#define MSGPOOL (MSGMNI*MSGMNB/1024)  /* size in kilobytes of message pool */
+#define MSGPOOL (MSGMNI * MSGMNB) /* size in bytes of message pool */
 #define MSGTQL  MSGMNB            /* number of system message headers */
 #define MSGMAP  MSGMNB            /* number of entries in message map */
 #define MSGSSZ  16                /* message segment size */
-#define __MSGSEG ((MSGPOOL*1024)/ MSGSSZ) /* max no. of segments */
-#define MSGSEG (__MSGSEG <= 0xffff ? __MSGSEG : 0xffff)
 
 #ifdef __KERNEL__
 #include <linux/list.h>

Index: linux-2.6.24-rc4/ipc/msg.c
===================================================================

ipc/msg.c +6 -1

@@ -27,6 +27,7 @@
 #include <linux/msg.h>
 #include <linux/spinlock.h>
 #include <linux/init.h>
+#include <linux/mm.h>
 #include <linux/proc_fs.h>
 #include <linux/list.h>
 #include <linux/security.h>

@@ -81,10 +82,25 @@ static int sysvipc_msg_proc_show(struct 
 
 static void __msg_init_ns(struct ipc_namespace *ns, struct ipc_ids *ids)
 {
+	struct sysinfo i;
+	unsigned long allowed;
+
 	ns->ids[IPC_MSG_IDS] = ids;
 	ns->msg_ctlmax = MSGMAX;
 	ns->msg_ctlmnb = MSGMNB;
-	ns->msg_ctlmni = MSGMNI;
+
+	/*

ipc/msg.c static int sysvipc_msg_proc_show(struct · line 102

Quoted 10 lines

ipc/msg.c +10 -0

+	 * Scale msgmni with the available memory size: the memory dedicated
+	 * to msg queues should occupy 1/32 of the available memory:
+	 * up to 8MB       : msgmni = 16 (MSGMNI)
+	 * 4 GB            : msgmni = 8K
+	 * more than 16 GB : msgmni = 32K (IPCMNI)
+	 */
+	si_meminfo(&i);
+	allowed = ((i.totalram / MSG_MEM_SCALE) * i.mem_unit) / MSGMNB;
+	ns->msg_ctlmni = min((unsigned long) IPCMNI,
+			max((unsigned long) MSGMNI, allowed));

The space after the (typecast) isn't useful IMO.

Please use min_t rather than the open-coded casts.

Even better would be to sort out the types so that neither casts nor min_t are needed.

What about highmem machines? For those we usually want to scale data structures according to the amount of direct-addressable memory (ie:
lowmem) rather than acording to total physical memory. I haven't a clue

how this consideration would be addressed when ipc-namespaces is taken into consideration.

I'd suggest the addition of a printk telling people what value the kernel calculated.

We should ensure that the calculated value is never _less_ than what the kernel was previously giving - to avoid breaking existing things.

It's a bit of a concern that a change like this can cause an application to work OK on machine A but then fail when it is taken over to (smaller) machine B.