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

From: Mel Gorman <mgorman@suse.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 <redacted>
Signed-off-by: Mel Gorman <mgorman@suse.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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