Date: Wed, 22 Jan 2003 17:56:00 -0500 From: Bosko Milekic <bmilekic@unixdaemons.com> To: Alfred Perlstein <bright@mu.org> Cc: Andrew Gallatin <gallatin@cs.duke.edu>, arch@FreeBSD.ORG Subject: Re: M_ flags summary. Message-ID: <20030122175600.A77460@unixdaemons.com> In-Reply-To: <20030122215424.GV42333@elvis.mu.org>; from bright@mu.org on Wed, Jan 22, 2003 at 01:54:24PM -0800 References: <20030122023246.GP42333@elvis.mu.org> <20030121224148.A75236@unixdaemons.com> <20030121.222025.101592442.imp@bsdimp.com> <20030122100253.A76397@unixdaemons.com> <0aef01c2c23d$0f1ae690$52557f42@errno.com> <20030122155457.A77036@unixdaemons.com> <15919.4208.394911.712558@grasshopper.cs.duke.edu> <20030122215424.GV42333@elvis.mu.org>
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On Wed, Jan 22, 2003 at 01:54:24PM -0800, Alfred Perlstein wrote:
> * Andrew Gallatin <gallatin@cs.duke.edu> [030122 13:43] wrote:
> >
> > The taste "problem" here is that it always used to be safe to sleep
> > in a process context. That's not true anymore. Now its safe to
> > sleep in a process context if you're not holding any mutexes. So
> > there are pleny of sleepable allocation bugs lurking.
> >
> > If we want to catch sleepable allocation bugs right up front, I
> > suggest we put this:
> >
> > if (!(flags & M_NOWAIT)) {
> > WITNESS_SLEEP(1, NULL);
> > }
> >
> > at the top of malloc, and at the top of all entry points to the mbuf
> > allocator. Eg, before the system has a chance to pull the allocation
> > off of some cache which will succeed 99.5% of the time, except when
> > the system is under memory pressure.
> >
> > Sorry for dragging this in another direction..
>
> This is actually a very good idea. It's too bad that one needs witness
> to catch this though. Can you add it, or shall i do it tonight?
It would be great if you did this for the mbuf code (the malloc()
code apparently, as John points out, already does it). If anything, I
think this is the one valuable thing we got out of this discussion.
> --
> -Alfred Perlstein [alfred@freebsd.org]
> 'Instead of asking why a piece of software is using "1970s technology,"
> start asking why software is ignoring 30 years of accumulated wisdom.'
--
Bosko Milekic * bmilekic@unixdaemons.com * bmilekic@FreeBSD.org
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