netdev - Re: [PATCH 01/12] netvm: Prevent a stream-specific deadlock

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Message-Id: <20120511.011034.557833140906762226.davem@davemloft.net>
Date:	Fri, 11 May 2012 01:10:34 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	mgorman@...e.de
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	netdev@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, Trond.Myklebust@...app.com,
	neilb@...e.de, hch@...radead.org, a.p.zijlstra@...llo.nl,
	michaelc@...wisc.edu, emunson@...bm.net
Subject: Re: [PATCH 01/12] netvm: Prevent a stream-specific deadlock

From: Mel Gorman <mgorman@...e.de>
Date: Thu, 10 May 2012 14:54:14 +0100

> It could happen that all !SOCK_MEMALLOC sockets have buffered so
> much data that we're over the global rmem limit. This will prevent
> SOCK_MEMALLOC buffers from receiving data, which will prevent userspace
> from running, which is needed to reduce the buffered data.
> 
> Fix this by exempting the SOCK_MEMALLOC sockets from the rmem limit.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

This introduces an invariant which I am not so sure is enforced.

With this change it is absolutely required that once a socket
becomes SOCK_MEMALLOC it must never _ever_ lose that attribute.

Otherwise we can end up liberating global rmem tokens which we never
actually took.
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