9eefe520c8
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>
92 lines
2.2 KiB
C
92 lines
2.2 KiB
C
/*
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* linux/ipc/ipcns_notifier.c
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* Copyright (C) 2007 BULL SA. Nadia Derbey
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*
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* Notification mechanism for ipc namespaces:
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* The callback routine registered in the memory chain invokes the ipcns
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* notifier chain with the IPCNS_MEMCHANGED event.
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* Each callback routine registered in the ipcns namespace recomputes msgmni
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* for the owning namespace.
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*/
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#include <linux/msg.h>
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#include <linux/rcupdate.h>
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#include <linux/notifier.h>
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#include <linux/nsproxy.h>
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#include <linux/ipc_namespace.h>
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#include "util.h"
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static BLOCKING_NOTIFIER_HEAD(ipcns_chain);
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static int ipcns_callback(struct notifier_block *self,
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unsigned long action, void *arg)
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{
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struct ipc_namespace *ns;
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switch (action) {
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case IPCNS_MEMCHANGED: /* amount of lowmem has changed */
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case IPCNS_CREATED:
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case IPCNS_REMOVED:
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/*
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* It's time to recompute msgmni
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*/
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ns = container_of(self, struct ipc_namespace, ipcns_nb);
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/*
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* No need to get a reference on the ns: the 1st job of
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* free_ipc_ns() is to unregister the callback routine.
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* blocking_notifier_chain_unregister takes the wr lock to do
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* it.
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* When this callback routine is called the rd lock is held by
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* blocking_notifier_call_chain.
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* So the ipc ns cannot be freed while we are here.
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*/
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recompute_msgmni(ns);
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break;
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default:
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break;
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}
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return NOTIFY_OK;
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}
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int register_ipcns_notifier(struct ipc_namespace *ns)
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{
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int rc;
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memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
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ns->ipcns_nb.notifier_call = ipcns_callback;
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ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
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rc = blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
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if (!rc)
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ns->auto_msgmni = 1;
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return rc;
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}
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int cond_register_ipcns_notifier(struct ipc_namespace *ns)
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{
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int rc;
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memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
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ns->ipcns_nb.notifier_call = ipcns_callback;
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ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
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rc = blocking_notifier_chain_cond_register(&ipcns_chain,
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&ns->ipcns_nb);
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if (!rc)
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ns->auto_msgmni = 1;
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return rc;
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}
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void unregister_ipcns_notifier(struct ipc_namespace *ns)
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{
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blocking_notifier_chain_unregister(&ipcns_chain, &ns->ipcns_nb);
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ns->auto_msgmni = 0;
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}
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int ipcns_notify(unsigned long val)
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{
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return blocking_notifier_call_chain(&ipcns_chain, val, NULL);
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}
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