This is a rework of Yuwen's patch [1] that adds writeback bio
batching support to zram, which can improve throughput of
writeback operation.

v1->v2:
- moved pp-slot ownership to req before submission (pp_ctl doesn't own it
  anymore after it's assigned to the req)
- do not take spin-lock in bach_limit handler
- dropped wb_limit_lock
- moved wb_limt accounting to pre-submit and completion stages
- introduced simple wb_limit helpers
- more comments and cleanups

[1] https://lore.kernel.org/linux-block/tencent_0FBBFC8AE0B97BC63B5D47CE1FF2BABFDA09@qq.com/

Sergey Senozhatsky (3):
  zram: add writeback batch size device attr
  zram: take write lock in wb limit store handlers
  zram: drop wb_limit_lock

Yuwen Chen (1):
  zram: introduce writeback bio batching support

 drivers/block/zram/zram_drv.c | 410 +++++++++++++++++++++++++++-------
 drivers/block/zram/zram_drv.h |   2 +-
 2 files changed, 326 insertions(+), 86 deletions(-)

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2.51.2.1041.gc1ab5b90ca-goog