[PATCH 0/2] Improve Zram by separating compression context from kswapd

[Qun-Wei Lin <qun-wei.lin@mediatek.com>]

This patch series introduces a new mechanism called kcompressd to
improve the efficiency of memory reclaiming in the operating system. The
main goal is to separate the tasks of page scanning and page compression
into distinct processes or threads, thereby reducing the load on the
kswapd thread and enhancing overall system performance under high memory
pressure conditions.

Problem:
 In the current system, the kswapd thread is responsible for both
 scanning the LRU pages and compressing pages into the ZRAM. This
 combined responsibility can lead to significant performance bottlenecks,
 especially under high memory pressure. The kswapd thread becomes a
 single point of contention, causing delays in memory reclaiming and
 overall system performance degradation.

Target:
 The target of this invention is to improve the efficiency of memory
 reclaiming. By separating the tasks of page scanning and page
 compression into distinct processes or threads, the system can handle
 memory pressure more effectively.

Patch 1:
- Introduces 2 new feature flags, BLK_FEAT_READ_SYNCHRONOUS and
  SWP_READ_SYNCHRONOUS_IO.

Patch 2:
- Implemented the core functionality of Kcompressd and made necessary
  modifications to the zram driver to support it.

In our handheld devices, we found that applying this mechanism under high
memory pressure scenarios can increase the rate of pgsteal_anon per second
by over 260% compared to the situation with only kswapd.

Qun-Wei Lin (2):
  mm: Split BLK_FEAT_SYNCHRONOUS and SWP_SYNCHRONOUS_IO into separate
    read and write flags
  kcompressd: Add Kcompressd for accelerated zram compression

 drivers/block/brd.c             |   3 +-
 drivers/block/zram/Kconfig      |  11 ++
 drivers/block/zram/Makefile     |   3 +-
 drivers/block/zram/kcompressd.c | 340 ++++++++++++++++++++++++++++++++
 drivers/block/zram/kcompressd.h |  25 +++
 drivers/block/zram/zram_drv.c   |  21 +-
 drivers/nvdimm/btt.c            |   3 +-
 drivers/nvdimm/pmem.c           |   5 +-
 include/linux/blkdev.h          |  24 ++-
 include/linux/swap.h            |  31 +--
 mm/memory.c                     |   4 +-
 mm/page_io.c                    |   6 +-
 mm/swapfile.c                   |   7 +-
 13 files changed, 446 insertions(+), 37 deletions(-)
 create mode 100644 drivers/block/zram/kcompressd.c
 create mode 100644 drivers/block/zram/kcompressd.h

-- 
2.45.2