[RFC PATCH 0/4] mm/shmem: optimize read performance with folio batching

[Chi Zhiling <chizhiling@163.com>]

From: Chi Zhiling <chizhiling@kylinos.cn>

This series optimizes shmem read performance by implementing folio
batching in the read path and eliminating unnecessary lock operations.

Performance testing with fio:
(--ioengine=sync --rw=read --size=1G --runtime=120)

shmem (THP disabled):
  bs=1M:   11.4 GiB/s
  bs=64k:  11.1 GiB/s
  bs=4k:   3814 MiB/s

shmem (THP disabled) + fbatch:
  bs=1M:   12.8 GiB/s (+12%)
  bs=64k:  12.3 GiB/s (+11%)
  bs=4k:   3783 MiB/s (-0.8%)

shmem (THP enabled):
  bs=1M:   13.8 GiB/s
  bs=64k:  13.1 GiB/s
  bs=4k:   3851 MiB/s

shmem (THP enabled) + fbatch:
  bs=1M:   14.0 GiB/s (+1%)
  bs=64k:  13.4 GiB/s (+2%)
  bs=4k:   3811 MiB/s (-1%)

shmem preallocated via fallocate (THP disabled):
  bs=1M:   24.0 GiB/s
  bs=64k:  22.5 GiB/s
  bs=4k:   4670 MiB/s

shmem preallocated via fallocate (THP disabled) + fbatch:
  bs=1M:   29.3 GiB/s (+22%)
  bs=64k:  26.7 GiB/s (+19%)
  bs=4k:   4654 MiB/s (-0.3%)

shmem preallocated via fallocate (THP enabled):
  bs=1M:   24.0 GiB/s
  bs=64k:  22.9 GiB/s
  bs=4k:   4698 MiB/s

shmem preallocated via fallocate (THP enabled) + fbatch:
  bs=1M:   34.3 GiB/s (+43%)
  bs=64k:  31.5 GiB/s (+38%)
  bs=4k:   4689 MiB/s (-0.2%)


Chi Zhiling (4):
  mm/shmem: add SGP_GET to get unlocked folio
  mm/shmem: use SGP_GET in read operations
  mm/shmem: optimize file read with folio batching
  mm/shmem: make SGP_NOALLOC succeed on hole like SGP_READ

 include/linux/shmem_fs.h |   5 +-
 mm/khugepaged.c          |   2 +-
 mm/shmem.c               | 132 ++++++++++++++++++++++++++++++++-------
 3 files changed, 112 insertions(+), 27 deletions(-)

-- 
2.43.0