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

From: Mel Gorman
Date: Mon May 14 2012 - 06:56:08 EST

On Fri, May 11, 2012 at 01:10:34AM -0400, David Miller wrote:
> From: Mel Gorman <mgorman@xxxxxxx>
> 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@xxxxxxxxx>
> > Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> 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.

This is effectively true. In the NFS case, the flag is cleared on
swapoff after all the entries have been paged in. In the NBD case,
SOCK_MEMALLOC is left set until the socket is destroyed. I'll update the

Mel Gorman
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