[PATCHv2 0/8] zram: Support multiple compression streams

From: Sergey Senozhatsky
Date: Tue Oct 04 2022 - 22:40:31 EST


This series adds support for multiple (per-CPU)
compression streams (at point only 2). 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 defalte 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

-- 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

Sergey Senozhatsky (8):
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
documentation: Add recompression documentation
zram: Add recompression algorithm choice to Kconfig
zram: Add recompress flag to read_block_state()
zram: correct typos

Documentation/admin-guide/blockdev/zram.rst | 64 ++-
drivers/block/zram/Kconfig | 52 +++
drivers/block/zram/zcomp.c | 6 +-
drivers/block/zram/zcomp.h | 2 +-
drivers/block/zram/zram_drv.c | 436 +++++++++++++++++---
drivers/block/zram/zram_drv.h | 16 +-
6 files changed, 506 insertions(+), 70 deletions(-)