linux-kernel - Re: [RFC] log out-of-virtual-memory events

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Message-ID: <20070518091606.GA1010@lnx-holt.americas.sgi.com>
Date:	Fri, 18 May 2007 04:16:07 -0500
From:	Robin Holt <holt@....com>
To:	Andrea Righi <righiandr@...rs.sourceforge.net>
Cc:	Rik van Riel <riel@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [RFC] log out-of-virtual-memory events

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.

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.

I think this may be a good fit.

Good Luck,
Robin
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