[RFC PATCH v2 00/19] mm: process/cgroup ksm support

[Stefan Roesch <shr@devkernel.io>]

So far KSM can only be enabled by calling madvise for memory regions. What is
required to enable KSM for more workloads is to enable / disable it at the
process / cgroup level.

Use case:
The madvise call is not available in the programming language. An example for
this are programs with forked workloads using a garbage collected language without
pointers. In such a language madvise cannot be made available.

In addition the addresses of objects get moved around as they are garbage
collected. KSM sharing needs to be enabled "from the outside" for these type of
workloads.

Experiments with using UKSM have shown a capacity increase of around 20%.


1. New options for prctl system command
This patch series adds two new options to the prctl system call. The first
one allows to enable KSM at the process level and the second one to query the
setting.

The setting will be inherited by child processes.

With the above setting, KSM can be enabled for the seed process of a cgroup
and all processes in the cgroup will inherit the setting.

2. Changes to KSM processing
When KSM is enabled at the process level, the KSM code will iterate over all
the VMA's and enable KSM for the eligible VMA's.

When forking a process that has KSM enabled, the setting will be inherited by
the new child process.

In addition when KSM is disabled for a process, KSM will be disabled for the
VMA's where KSM has been enabled.

3. Add general_profit metric
The general_profit metric of KSM is specified in the documentation, but not
calculated. This adds the general profit metric to /sys/kernel/debug/mm/ksm.

4. Add more metrics to ksm_stat
This adds the process profit and ksm type metric to /proc/<pid>/ksm_stat.

5. Add more tests to ksm_tests
This adds an option to specify the merge type to the ksm_tests. This allows to
test madvise and prctl KSM. It also adds a new option to query if prctl KSM has
been enabled. It adds a fork test to verify that the KSM process setting is
inherited by client processes.


Changes:
- V2:
  - Added use cases to the cover letter
  - Removed the tracing patch from the patch series and posted it as an
    individual patch
  - Refreshed repo



Stefan Roesch (19):
  mm: add new flag to enable ksm per process
  mm: add flag to __ksm_enter
  mm: add flag to __ksm_exit call
  mm: invoke madvise for all vmas in scan_get_next_rmap_item
  mm: support disabling of ksm for a process
  mm: add new prctl option to get and set ksm for a process
  mm: split off pages_volatile function
  mm: expose general_profit metric
  docs: document general_profit sysfs knob
  mm: calculate ksm process profit metric
  mm: add ksm_merge_type() function
  mm: expose ksm process profit metric in ksm_stat
  mm: expose ksm merge type in ksm_stat
  docs: document new procfs ksm knobs
  tools: add new prctl flags to prctl in tools dir
  selftests/vm: add KSM prctl merge test
  selftests/vm: add KSM get merge type test
  selftests/vm: add KSM fork test
  selftests/vm: add two functions for debugging merge outcome

 Documentation/ABI/testing/sysfs-kernel-mm-ksm |   8 +
 Documentation/admin-guide/mm/ksm.rst          |   8 +-
 fs/proc/base.c                                |   5 +
 include/linux/ksm.h                           |  19 +-
 include/linux/sched/coredump.h                |   1 +
 include/uapi/linux/prctl.h                    |   2 +
 kernel/sys.c                                  |  29 ++
 mm/ksm.c                                      | 114 +++++++-
 tools/include/uapi/linux/prctl.h              |   2 +
 tools/testing/selftests/mm/Makefile           |   3 +-
 tools/testing/selftests/mm/ksm_tests.c        | 254 +++++++++++++++---
 11 files changed, 389 insertions(+), 56 deletions(-)


base-commit: 234a68e24b120b98875a8b6e17a9dead277be16a
-- 
2.30.2