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author | Nadia Derbey <Nadia.Derbey@bull.net> | 2008-07-25 10:48:08 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-07-25 19:53:42 +0200 |
commit | 9eefe520c814f6f62c5d36a2ddcd3fb99dfdb30e (patch) | |
tree | 064ce99674f144b681f8d365d1e20d99c8078d0c /ipc/ipcns_notifier.c | |
parent | ipc: use simple_read_from_buffer() (diff) | |
download | linux-9eefe520c814f6f62c5d36a2ddcd3fb99dfdb30e.tar.xz linux-9eefe520c814f6f62c5d36a2ddcd3fb99dfdb30e.zip |
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 <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>
Diffstat (limited to '')
-rw-r--r-- | ipc/ipcns_notifier.c | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/ipc/ipcns_notifier.c b/ipc/ipcns_notifier.c index 70ff09183f7b..b9b31a4f77e1 100644 --- a/ipc/ipcns_notifier.c +++ b/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) |