Hello, 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 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. 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 Sergey Senozhatsky (9): 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: Clarify writeback_store() comment zram: Use IS_ERR_VALUE() to check for zs_malloc() errors Documentation/admin-guide/blockdev/zram.rst | 64 ++- drivers/block/zram/Kconfig | 55 +++ drivers/block/zram/zcomp.c | 6 +- drivers/block/zram/zcomp.h | 2 +- drivers/block/zram/zram_drv.c | 458 +++++++++++++++++--- drivers/block/zram/zram_drv.h | 16 +- 6 files changed, 526 insertions(+), 75 deletions(-) -- 2.38.0.413.g74048e4d9e-goog
