memcg: initiate deprecation of v1 soft limit

Memcg v1 provides soft limit functionality for the best effort memory
sharing between multiple workloads on a system.  It is usually triggered
through kswapd and at the moment does not reclaim kernel memory.

Memcg v2 provides more straightforward best effort (memory.low) and hard
protection (memory.min) functionalities.  Let's initiate the deprecation
of soft limit from v1 and gather if v2 needs something more to move the
existing v1 users to v2 regarding soft limit.

Link: https://lkml.kernel.org/r/20240814220021.3208384-3-shakeel.butt@linux.dev


Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: T.J. Mercier <tjmercier@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>