linux-kernel - Re: [PATCH 02/10] mm: system wide ALLOC_NO

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Message-ID: <20070806201257.GG11115@waste.org>
Date:	Mon, 6 Aug 2007 15:12:57 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Daniel Phillips <phillips@...nq.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Phillips <phillips@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Steve Dickson <SteveD@...hat.com>
Subject: Re: [PATCH 02/10] mm: system wide ALLOC_NO_WATERMARK

On Mon, Aug 06, 2007 at 11:51:45AM -0700, Christoph Lameter wrote:
> On Mon, 6 Aug 2007, Daniel Phillips wrote:
> 
> > On Monday 06 August 2007 11:42, Christoph Lameter wrote:
> > > On Mon, 6 Aug 2007, Daniel Phillips wrote:
> > > > Currently your system likely would have died here, so ending up
> > > > with a reserve page temporarily on the wrong node is already an
> > > > improvement.
> > >
> > > The system would have died? Why?
> > 
> > Because a block device may have deadlocked here, leaving the system 
> > unable to clean dirty memory, or unable to load executables over the 
> > network for example.
> 
> So this is a locking problem that has not been taken care of?

No.

It's very simple:

1) memory becomes full
2) we try to free memory by paging or swapping
3) I/O requires a memory allocation which fails because memory is full
4) box dies because it's unable to dig itself out of OOM

Most I/O paths can deal with this by having a mempool for their I/O
needs. For network I/O, this turns out to be prohibitively hard due to
the complexity of the stack.

-- 
Mathematics is the supreme nostalgia of our time.
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