zswap: make shrinking memcg-aware

Currently, we only have a single global LRU for zswap.  This makes it
impossible to perform worload-specific shrinking - an memcg cannot
determine which pages in the pool it owns, and often ends up writing pages
from other memcgs.  This issue has been previously observed in practice
and mitigated by simply disabling memcg-initiated shrinking:

https://lore.kernel.org/all/[email protected]/T/#u

This patch fully resolves the issue by replacing the global zswap LRU
with memcg- and NUMA-specific LRUs, and modify the reclaim logic:

a) When a store attempt hits an memcg limit, it now triggers a
   synchronous reclaim attempt that, if successful, allows the new
   hotter page to be accepted by zswap.
b) If the store attempt instead hits the global zswap limit, it will
   trigger an asynchronous reclaim attempt, in which an memcg is
   selected for reclaim in a round-robin-like fashion.

[[email protected]: use correct function for the onlineness check, use mem_cgroup_iter_break()]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: drop the pool's reference at the end of the writeback step]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Domenico Cerasuolo <[email protected]>
Co-developed-by: Nhat Pham <[email protected]>
Signed-off-by: Nhat Pham <[email protected]>
Tested-by: Bagas Sanjaya <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Dan Streetman <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Vitaly Wool <[email protected]>
Cc: Yosry Ahmed <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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