[PATCHv5 00/13] zram: Support multiple compression streams

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Hello,

	This series adds support for multiple compression streams.
The main idea is that different compression algorithms have different
characteristics and zram may benefit when it uses a combination of
algorithms: a default algorithm that is faster but have lower
compression rate and a secondary algorithm that can use higher
compression rate at a price of slower compression/decompression.

	There are several use-case for this functionality:

- huge pages re-compression: zstd or deflate can successfully
compress huge pages (~50% of huge pages on my synthetic ChromeOS
tests), IOW pages that lzo was not able to compress.

- idle pages re-compression: idle/cold pages sit in the memory
and we may reduce zsmalloc memory usage if we recompress those
idle pages.

	User-space has a number of ways to control the behavior
and impact of zram recompression: what type of pages should be
recompressed, size watermarks, etc. Please refer to documentation
patch.

v5:
-- Addressed (very valuable) review feedback from Minchan
-- Extended documentation
-- We now do chain recompression, tryin algos in order of their priority
-- Support up to 4 compression streams
-- Added named parameters to recomp_algorithm and recompress sysfs knobs
-- Cherry-picked patch from Alexey
-- Store algo priority in mete flags
-- Renamed some fo the flags
-- Added incompressible bit to block state output
-- Added incompressible writeback
-- etc.

v4:
-- added IS_ERR_VALUE patch (Andrew)
-- documented SIZE units (bytes) (Andrew)
-- re-phrased writeback BIO error comment (Andrew)
-- return zs_malloc() error code from zram_recompress()
-- do not lose zram_recompress() error in recompress_store()
-- corrected a typo
-- fixed previous rebase errors
-- rebased the series

v3:
-- conditionally reschedule during recompression loop so that
   we don't stall RCU grace periods
-- fixed a false-positive WARN_ON

v2:
-- rebased
-- mark completely incompressible pages (neither default nor secondary
   algorithm can compress them) with a new flag so that we don't attempt
   to recompress them all the time

Alexey Romanov (1):
  zram: add size class equals check into recompression

Sergey Senozhatsky (12):
  zram: Preparation for multi-zcomp support
  zram: Add recompression algorithm sysfs knob
  zram: Factor out WB and non-WB zram read functions
  zram: Introduce recompress sysfs knob
  zram: Add recompress flag to read_block_state()
  zram: Clarify writeback_store() comment
  zram: Use IS_ERR_VALUE() to check for zs_malloc() errors
  zram: remove redundant checks from zram_recompress()
  zram: Add algo parameter support to zram_recompress()
  documentation: Add zram recompression documentation
  zram: add incompressible writeback
  zram: Add incompressible flag to read_block_state()

 Documentation/admin-guide/blockdev/zram.rst | 100 +++-
 drivers/block/zram/Kconfig                  |   9 +
 drivers/block/zram/zcomp.c                  |   6 +-
 drivers/block/zram/zcomp.h                  |   2 +-
 drivers/block/zram/zram_drv.c               | 604 +++++++++++++++++---
 drivers/block/zram/zram_drv.h               |  22 +-
 include/linux/zsmalloc.h                    |   2 +
 mm/zsmalloc.c                               |  21 +
 8 files changed, 685 insertions(+), 81 deletions(-)

-- 
2.38.1.431.g37b22c650d-goog