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Date:	Fri, 18 May 2007 17:55:10 +0200 (MEST)
From:	Andrea Righi <righiandr@...rs.sourceforge.net>
To:	Robin Holt <holt@....com>
Cc:	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC] log out-of-virtual-memory events

Robin Holt wrote:
> On Fri, May 18, 2007 at 09:50:03AM +0200, Andrea Righi wrote:
>> Rik van Riel wrote:
>>> Andrea Righi wrote:
>>>> I'm looking for a way to keep track of the processes that fail to
>>>> allocate new
>>>> virtual memory. What do you think about the following approach
>>>> (untested)?
>>> Looks like an easy way for users to spam syslogd over and
>>> over and over again.
>>>
>>> At the very least, shouldn't this be dependant on print_fatal_signals?
>>>
>> Anyway, with print-fatal-signals enabled a user could spam syslogd too, simply
>> with a (char *)0 = 0 program, but we could always identify the spam attempts
>> logging the process uid...
>>
>> In any case, I agree, it should depend on that patch...
>>
>> What about adding a simple msleep_interruptible(SOME_MSECS) at the end of
>> log_vm_enomem() or, at least, a might_sleep() to limit the potential spam/second
>> rate?
> 
> An msleep will slow down this process, but do nothing about slowing
> down the amount of logging.  Simply fork a few more processes and all
> you are doing with msleep is polluting the pid space.
> 

Very true.

> What about a throttling similar to what ia64 does for floating point
> assist faults (handle_fpu_swa()).  There is a thread flag to not log
> the events at all.  It is rate throttled globally, but uses per cpu
> variables for early exits.  This algorithm scaled well to a thousand
> cpus.

Actually using printk_ratelimit() should be enough... BTW print_fatal_signals()
should use it too.

-Andrea

---

Signed-off-by: Andrea Righi <a.righi@...eca.it>

diff -urpN linux-2.6.21/mm/mmap.c linux-2.6.21-vm-log-enomem/mm/mmap.c
--- linux-2.6.21/mm/mmap.c	2007-04-26 05:08:32.000000000 +0200
+++ linux-2.6.21-vm-log-enomem/mm/mmap.c	2007-05-18 17:17:32.000000000 +0200
@@ -77,6 +77,29 @@ int sysctl_max_map_count __read_mostly =
 atomic_t vm_committed_space = ATOMIC_INIT(0);
 
 /*
+ * Print current process informations when it fails to allocate new virtual
+ * memory.
+ */
+static inline void log_vm_enomem(void)
+{
+	unsigned long total_vm = 0;
+	struct mm_struct *mm;
+
+	if (unlikely(!printk_ratelimit()))
+		return;
+
+	task_lock(current);
+	mm = current->mm;
+	if (mm)
+		total_vm = mm->total_vm;
+	task_unlock(current);
+
+	printk(KERN_INFO
+	       "out of virtual memory for process %d (%s): total_vm=%lu, uid=%d\n",
+		current->pid, current->comm, total_vm, current->uid);
+}
+
+/*
  * Check that a process has enough memory to allocate a new virtual
  * mapping. 0 means there is enough memory for the allocation to
  * succeed and -ENOMEM implies there is not.
@@ -175,6 +198,7 @@ int __vm_enough_memory(long pages, int c
 		return 0;
 error:
 	vm_unacct_memory(pages);
+	log_vm_enomem();
 
 	return -ENOMEM;
 }
-
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