[PATCH 0/7] zsmalloc: redesign object alloc API

[Sergey Senozhatsky]

Both zram and zswap already have per-entry structures that store zsmalloc
handles, so allocating a separate handle_cachep object per stored page is
redundant.  This series embeds struct zs_handle directly into zram and
zswap entries and drops handle_cachep, saving 8 bytes and a slab
alloc/free per stored object (2MB per 1GB of swapped out 4K pages).

It also folds zs_malloc() and zs_obj_write() into zs_store() so we don't
take pool->lock and look up object location again right after allocation.

A simple zram test on a 24-vCPU VM
==================================
165 fewer kernel instructions and 0.7-1.8% fewer kernel cycles per write;
lz4 single writer +2.3% IOPS / -2.6% average latency;
24 writers +0.9-+1.0% IOPS; no regressions.
Memory: 8 bytes less per stored page.

Sergey Senozhatsky (7):
  zram: drop stale comment in write_incompressible_page()
  zram: drop get_slot_handle() and set_slot_handle()
  zsmalloc: switch handle type to struct zs_handle
  zram: allocate zsmalloc object under slot lock
  zsmalloc: embed struct zs_handle into zram and zswap entries
  zsmalloc: fold zs_obj_write() into zs_store()
  zsmalloc: constify struct zs_handle pointer in read-only functions

 Documentation/admin-guide/mm/slab.rst        |   2 +-
 Documentation/core-api/memory-allocation.rst |   2 +-
 Documentation/mm/zsmalloc.rst                |   8 +-
 drivers/block/zram/Kconfig                   |   1 +
 drivers/block/zram/zram_drv.c                | 130 +++++-------
 drivers/block/zram/zram_drv.h                |  10 +-
 include/linux/zsmalloc.h                     |  37 +++-
 mm/Kconfig                                   |   3 +
 mm/zsmalloc.c                                | 204 +++++++++++--------
 mm/zswap.c                                   |  21 +-
 10 files changed, 229 insertions(+), 189 deletions(-)

-- 
2.56.0.398.g882cbad275-goog