linux-kernel - Re: mmap'ed memory in core files ?

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Message-ID: <20080702115201.GA12974@brong.net>
Date:	Wed, 2 Jul 2008 21:52:01 +1000
From:	Bron Gondwana <brong@...tmail.fm>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Rob Mueller <robm@...tmail.fm>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Bron Gondwana <brong@...tmail.fm>,
	Philippe De Muyter <phdm@...qel.be>,
	linux-kernel@...r.kernel.org
Subject: Re: mmap'ed memory in core files ?

On Wed, Jul 02, 2008 at 01:07:22PM +0200, Andi Kleen wrote:
> "Rob Mueller" <robm@...tmail.fm> writes:
> >
> > It's clearly sparse, but slightly unintuitive that the ulimit doesn't
> > actually limit the filesize, just the size of the data written to the
> > file.
> 
> It's the only sane semantic. Imagine ulimit would limit the address
> range as you seem to be asking for. This means if you set e.g. ulimit
> -c 1G then the kernel would never dump any address (mmap or not) above
> 1GB. Never dumping the process stack for example. Clearly doesn't make
> any sense. And mmap'ed files are not different from any other 
> mappings in this regard.

Hmm.. the IO hit we got with those Cyrus crashes suggested that it was
more than just a small amount of IO being caused.  I didn't check if the
files were sparse or not.

I guess we can probably create a test case that recreates it, even if it's
just running up a dodgy Cyrus instance on the machine that had the crashes
before and deliberately recreating a broken cache file to trigger it.

Bron.
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