From 9eefe520c814f6f62c5d36a2ddcd3fb99dfdb30e Mon Sep 17 00:00:00 2001 From: Nadia Derbey Date: Fri, 25 Jul 2008 01:48:08 -0700 Subject: ipc: do not use a negative value to re-enable msgmni automatic recomputing 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 > /proc/sys/kernel/msgmni . sets msg_ctlmni to . 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 Cc: Solofo Ramangalahy Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/ipc_namespace.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include/linux/ipc_namespace.h') diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h index ea6c18a..ea330f9 100644 --- a/include/linux/ipc_namespace.h +++ b/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 */ -- cgit v1.1