foundations of per-cgroup memory pressure controlling.

foundations of per-cgroup memory pressure controlling.

This patch replaces all uses of struct sock fields' memory_pressure,
memory_allocated, sockets_allocated, and sysctl_mem to acessor
macros. Those macros can either receive a socket argument, or a mem_cgroup
argument, depending on the context they live in.

Since we're only doing a macro wrapping here, no performance impact at all is
expected in the case where we don't have cgroups disabled.

Signed-off-by: Glauber Costa <[email protected]>
Reviewed-by: Hiroyouki Kamezawa <[email protected]>
CC: David S. Miller <[email protected]>
CC: Eric W. Biederman <[email protected]>
CC: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>