[PATCH 0/4] workqueue: reduce the sizeof pool_workqueue

[Lai Jiangshan <laijs@linux.alibaba.com>]

The major memory ussage in workqueue is on the pool_workqueue.
The pool_workqueue has alignment requirement which often leads
to padding.

Reducing the memory usage for the pool_workqueue is valuable.

And 32bit system often has less memory, less workqueues,
less works, less concurrent flush_workqueue()s, so we can
slash the flush color on 32bit system to reduce memory usage

Before patch:
The sizeof the struct pool_workqueue is 256 bytes,
only 136 bytes is in use in 32bit system

After patch:
The sizeof the struct pool_workqueue is 128 bytes,
only 104 bytes is in use in 32bit system, there is still
room for future usage.

Setting WORK_STRUCT_COLOR_BITS to 3 can't reduce the sizeof
the struct pool_workqueue in 64bit system, unless combined
with big refactor for unbound pwq.

Lai Jiangshan (4):
  workqueue: fix a piece of comment about reserved bits for work flags
  workqueue: use BUILD_BUG_ON() for compile time test instead of
    WARN_ON()
  workqueue: add a BUILD_BUG_ON() to check the size of struct
    pool_workqueue
  workqueue: slash half memory usage in 32bit system

Cc: Tejun Heo <tj@kernel.org>

 include/linux/workqueue.h |  8 +++++++-
 kernel/workqueue.c        | 10 +++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

-- 
2.20.1