Re: [PATCH v5] alloc_tag: expose boot-time compression configuration

On Wed, Aug 5, 2026 at 10:29 AM Abhishek Bapat <[email protected]> wrote:
>
> Currently, userspace has limited visibility into the exact active
> runtime state of memory allocation profiling and its page extension
> compression ('sysctl.vm.mem_profiling={0|1|never}[,compressed]').
>
> While reading the sysctl provides basic on/off status, it is currently
> impossible for userspace to natively determine whether page-tag
> compression was successfully enabled without scraping dmesg boot logs.
>
> Add a new read-only sysctl representing how compression was configured
> at boot time.
>
> Signed-off-by: Abhishek Bapat <[email protected]>

Acked-by: Suren Baghdasaryan <[email protected]>

> ---
> v5 change:
> - More documentation and commit message refactoring.
>
> v4 change:
> - Documentation and commit message refactor.
>
> v3 change:
> - Added documentation about the behaviour details of the new sysctl.
>
> v2 change:
> - Moved from displaying the state in /proc/allocinfo to a new read-only
> sysctl.
>
>  Documentation/mm/allocation-profiling.rst | 11 +++++++++++
>  mm/alloc_tag.c                            |  6 ++++++
>  2 files changed, 17 insertions(+)
>
> diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst
> index c3a28467955f..b2ebcef8af6f 100644
> --- a/Documentation/mm/allocation-profiling.rst
> +++ b/Documentation/mm/allocation-profiling.rst
> @@ -43,6 +43,17 @@ sysctl:
>    warnings produced by allocations made while profiling is disabled and freed
>    when it's enabled.
>
> +  /proc/sys/vm/mem_profiling_compressed
> +
> +  1: Page alloc tag compression is enabled.
> +
> +  0: Page alloc tag compression is disabled.
> +
> +  This reflects a static boot-time configuration of how page allocation tags are
> +  stored (in page flags when compression is enabled and in page_ext when disabled).
> +  Toggling ``mem_profiling`` at runtime does not change the state of
> +  ``mem_profiling_compressed``.
> +
>  Runtime info:
>    /proc/allocinfo
>
> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
> index 84c5c3783ca4..b33410310477 100644
> --- a/mm/alloc_tag.c
> +++ b/mm/alloc_tag.c
> @@ -1303,6 +1303,12 @@ static const struct ctl_table memory_allocation_profiling_sysctls[] = {
>                 .mode           = 0644,
>                 .proc_handler   = proc_mem_profiling_handler,
>         },
> +       {
> +               .procname       = "mem_profiling_compressed",
> +               .data           = &mem_profiling_compressed,
> +               .mode           = 0444,
> +               .proc_handler   = proc_do_static_key,
> +       },
>  };
>
>  static void __init sysctl_init(void)
>
> base-commit: a946fa1d96648b92c9f37f0488e0e47a85f9e235
> --
> 2.55.0.508.g3f0d502094-goog
>