[PATCH v4 0/5] Implement writeback for zsmalloc

[Nhat Pham <nphamcs@gmail.com>]

Changelog:
v4:
  * Wrap the new LRU logic in CONFIG_ZPOOL (patch 3).
    (suggested by Minchan Kim)
v3:
  * Set pool->ops = NULL when pool->zpool_ops is null (patch 4).
  * Stop holding pool's lock when calling lock_zspage() (patch 5).
    (suggested by Sergey Senozhatsky)
  * Stop holding pool's lock when checking pool->ops and retries.
    (patch 5) (suggested by Sergey Senozhatsky)
  * Fix formatting issues (.shrink, extra spaces in casting removed).
    (patch 5) (suggested by Sergey Senozhatsky)

v2:
  * Add missing CONFIG_ZPOOL ifdefs (patch 5)
    (detected by kernel test robot).

Unlike other zswap's allocators such as zbud or z3fold, zsmalloc
currently lacks the writeback mechanism. This means that when the zswap
pool is full, it will simply reject further allocations, and the pages
will be written directly to swap.

This series of patches implements writeback for zsmalloc. When the zswap
pool becomes full, zsmalloc will attempt to evict all the compressed
objects in the least-recently used zspages.

There are 5 patches in this series:

Johannes Weiner (1):
  zswap: fix writeback lock ordering for zsmalloc

Nhat Pham (4):
  zsmalloc: Consolidate zs_pool's migrate_lock and size_class's locks
  zsmalloc: Add a LRU to zs_pool to keep track of zspages in LRU order
  zsmalloc: Add ops fields to zs_pool to store evict handlers
  zsmalloc: Implement writeback mechanism for zsmalloc

 mm/zsmalloc.c | 359 +++++++++++++++++++++++++++++++++++++++++---------
 mm/zswap.c    |  37 +++---
 2 files changed, 315 insertions(+), 81 deletions(-)

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2.30.2