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

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

v3 -> v4:
- fixed bdev block id leak (Yuwen)
- fixed missing pps index assignment (Yuwen)
- fixed preliminary wb IO completion slot release
- we now use bit 0 for writeback as well
- access bdev read slot block id under slot lock
- some other cleanups

Sergey Senozhatsky (5):
  zram: add writeback batch size device attr
  zram: take write lock in wb limit store handlers
  zram: drop wb_limit_lock
  zram: rework bdev block allocation
  zram: read slot block idx under slot lock

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

 drivers/block/zram/zram_drv.c | 452 ++++++++++++++++++++++++++--------
 drivers/block/zram/zram_drv.h |   2 +-
 2 files changed, 348 insertions(+), 106 deletions(-)

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2.52.0.rc1.455.g30608eb744-goog