From: Neil Brown <neilb@suse.de>
To: Andrew Morton <akpm@osdl.org>
Date: Sat, 5 Nov 2005 16:37:01 +1100
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Cc: cplk@itee.uq.edu.au, bunk@stusta.de, heiko.carstens@de.ibm.com,
       linux-kernel@vger.kernel.org, aherrman@de.ibm.com, dm-devel@redhat.com
Subject: Re: [PATCH resubmit] do_mount: reduce stack consumption
In-Reply-To: message from Andrew Morton on Friday November 4
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On Friday November 4, akpm@osdl.org wrote:
> cplk@itee.uq.edu.au wrote:
> >
> > > > > This part of the call trace is actually good for >1500 bytes of stack
> > > > > usage and is what kills us and should be fixed.
> > > > > I'm surprised that there are no other bug reports regarding DM and
> > > > > stack overflow with 4k stacks.
> > > > >...
> > > > 
> > > > There were some reports of dm+xfs overflows with 4k stacks on i386.
> > > > 
> > > > The xfs side was sorted out, but I son't know the state of the dm part.
> > > > 
> > > 
> > > The state is Very Bad, IMO.  At the very least, DM should struggle to the
> > > utmost to reduce the stack utilisation around that recursion point.
> > 
> > Neil Brown suggested a change to generic_make_request to convert recursion 
> > through it into iteration (see http://lkml.org/lkml/2005/9/2/34 ), but 
> > there was no discussion at the time.  Would this help with this case?
> 
> It certainly would.  That looks like a good thing to do some more work on.

Ok, I'll dust it off, make sure it seems to work (at the time I first
wrote it, I think it caused 'md' to deadlock) and submit it.

NeilBrown
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