linux-kernel - Re: [PATCH] fix quadratic behavior of shrink_dcache

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Message-Id: <20070209164018.e4d29be0.akpm@linux-foundation.org>
Date:	Fri, 9 Feb 2007 16:40:18 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Russ Cox" <rsc@...ch.com>
Cc:	"Miklos Szeredi" <miklos@...redi.hu>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix quadratic behavior of shrink_dcache_parent()

On Fri, 9 Feb 2007 19:23:31 -0500
"Russ Cox" <rsc@...ch.com> wrote:

> > "The file system mounted on /tmp/z in the example contains 2^50
> > directories".   heh.
> >
> > I do wonder how realistic this problem is in real life.
> 
> That's a fair concern, although I was trying this as part
> of evaluating how much someone could hose a system
> if we let them mount arbitrary FUSE servers.  And the
> answer is: they could make it completely unusable,
> requiring reboot.
> 
> I ran a later test that printed how deep it got into
> the file tree and it was only a few hundred thousand
> if I recall correctly.  A determined attacker might even
> manage to do this in a normal file system.
> 
> But sure, it's not a common case.  ;-)

Well that's a good point - sometimes people do crazy things on purpose.  We
were all University students once ;) 

The patches look nice and as I said, potentially of some use for memory
reclaim.  But I hope that someone who has worked on dcache.c more recently
than I has time to apply a toothcomb to this work.

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