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SubjectRe: [RESEND RFC PATCH v1 00/20] mm: process/cgroup ksm support
On 23.01.23 18:37, Stefan Roesch wrote:
> 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.

Did you stumble over the proposals from last year to enable this
per-process [1] and system-wide [2]? I remember there was also regarding
enabling it system-wide.

I'm going to point out the security aspect, and that e.g., Windows used
to enable it system-wide before getting taught by security experts
otherwise. Details on KSM and security aspects can be found in that thread.

Long story short: one has to be very careful with that and only enable
it for very carefully selected worklads. Letting a workload opt-in on a
VMA level is most probably safer than an admin blindly turning this on
for random processes ...

Last attempts got nacked ...

[1]
https://lore.kernel.org/all/20220517092701.1662641-1-xu.xin16@zte.com.cn/
[2] https://lore.kernel.org/all/20220609055658.703472-1-xu.xin16@zte.com.cn/

>
> 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 tracepoints to KSM
> Currently KSM has no tracepoints. This adds tracepoints to the key KSM functions
> to make it easier to debug KSM.
>
> 4. 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.
>
> 5. Add more metrics to ksm_stat
> This adds the process profit and ksm type metric to /proc/<pid>/ksm_stat.
>
> 6. 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.
>
>
> Stefan Roesch (20):
> 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: add tracepoints to ksm
> 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 +-
> MAINTAINERS | 1 +
> fs/proc/base.c | 5 +
> include/linux/ksm.h | 19 +-
> include/linux/sched/coredump.h | 1 +
> include/trace/events/ksm.h | 257 ++++++++++++++++++
> include/uapi/linux/prctl.h | 2 +
> kernel/sys.c | 29 ++
> mm/ksm.c | 134 ++++++++-
> tools/include/uapi/linux/prctl.h | 2 +
> tools/testing/selftests/vm/Makefile | 3 +-
> tools/testing/selftests/vm/ksm_tests.c | 254 ++++++++++++++---
> 13 files changed, 665 insertions(+), 58 deletions(-)
> create mode 100644 include/trace/events/ksm.h
>
>
> base-commit: c1649ec55708ae42091a2f1bca1ab49ecd722d55

--
Thanks,

David / dhildenb

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