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Date:      Tue, 08 Jan 2002 13:05:13 -0800
From:      Michael Smith <msmith@freebsd.org>
To:        Poul-Henning Kamp <phk@critter.freebsd.dk>
Cc:        Dan Moschuk <dan@FreeBSD.ORG>, "M. Warner Losh" <imp@village.org>, msmith@FreeBSD.ORG, stable@FreeBSD.ORG
Subject:   Re: Hang in md driver 
Message-ID:  <200201082105.g08L5D001648@mass.dis.org>
In-Reply-To: Your message of "Tue, 08 Jan 2002 21:50:00 %2B0100." <9566.1010523000@critter.freebsd.dk> 

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> In message <20020108142747.G3163@spirit.jaded.net>, Dan Moschuk writes:
> >
> >| >In message: <200201072026.g07KQUX01267@mass.dis.org>
> >| >            Michael Smith <msmith@FreeBSD.ORG> writes:
> >| >: This doesn't seem to address the problem; md(4) shouldn't hang when it 
> >| >: runs out of memory.
> >| >
> >| >We have systems that hange 1 time in 10 when booting when trying to
> >| >mount the mfs stuff... :-(
> >| 
> >| Well, there is no malloc_quota_used(9), so I can't do anything about it.
> >
> >What would be involved in writing one?  Work has me pretty busy, but I'd
> >like to take a stab at it.
> 
> I have no idea, sorry...

This wouldn't do it.

You really want to add an M_SHORTWAIT flag, and in kern/kern_malloc.c 
around line 162 (in -current anyway) pass a timeout to msleep.  If the 
timeout expires, return NULL.  The wait should be perhaps 1 second at 
most.

This would be simple to add to both -stable and -current, and since 
it doesn't change the behaviour of M_WAITOK, would not have any 
deleterious sideeffects.  You could then work your way through the 
M_WAITOK consumers, teaching the relevant ones how to deal with resource 
starvation other than by deadlocking.



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