Re: [PATCH v3] alloc_tag: expose profiling and compression states

On Mon, Aug 3, 2026 at 2:54=E2=80=AFPM Abhishek Bapat <abhishekbapat@google=
.com> 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=3D{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.
>
> Resolve this ambiguity by exposing the active compression state by
> adding a new read-only sysctl `vm.mem_profiling_compressed` to output the

"Resolve this ambiguity by exposing the active compression state by
adding a new read-only sysctl" sounds too elaborate. This also
conflicts with the documentation you added which states
"`mem_profiling_compressed` represents the state configured at boot
time", so your description of it representing "the active compression
state" is incorrect.
How about: "Add a new read-only sysctl representing how compression
was configured at boot time."?

> state.
>
> 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.
>
> Signed-off-by: Abhishek Bapat <[email protected]>
> ---
>  Documentation/mm/allocation-profiling.rst | 13 +++++++++++++
>  mm/alloc_tag.c                            |  6 ++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm=
/allocation-profiling.rst
> index c3a28467955f..3ad1e9aacb9a 100644
> --- a/Documentation/mm/allocation-profiling.rst
> +++ b/Documentation/mm/allocation-profiling.rst
> @@ -43,6 +43,19 @@ sysctl:
>    warnings produced by allocations made while profiling is disabled and =
freed
>    when it's enabled.
>
> +  /proc/sys/vm/mem_profiling_compressed
> +
> +  1: Page extension compression is enabled.

We are not compressing page extensions but rather page allocation
tags, so "Page extension compression" is misleading. I think "Page
allocation tag compression is enabled." would be better.

> +
> +  0: Page extension compression is disabled.
> +
> +  This control is read-only and reflects the compression status initiali=
zed at boot.
> +  Note that, unlike `mem_profiling`, which represents the current state =
of profiling,
> +  `mem_profiling_compressed` represents the state configured at boot tim=
e. Turning off
> +  profiling at runtime will implicitly make this sysctl effectively dorm=
ant. However, if
> +  profiling is toggled off and then toggled on again, it will resume wit=
h compression
> +  still enabled as long as the value of `mem_profiling_compressed` is 1.
> +
>  Runtime info:
>    /proc/allocinfo
>
> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
> index 52aece27b00e..877068241f06 100644
> --- a/mm/alloc_tag.c
> +++ b/mm/alloc_tag.c
> @@ -1303,6 +1303,12 @@ static const struct ctl_table memory_allocation_pr=
ofiling_sysctls[] =3D {
>                 .mode           =3D 0644,
>                 .proc_handler   =3D proc_mem_profiling_handler,
>         },
> +       {
> +               .procname       =3D "mem_profiling_compressed",
> +               .data           =3D &mem_profiling_compressed,
> +               .mode           =3D 0444,
> +               .proc_handler   =3D proc_do_static_key,
> +       },
>  };
>
>  static void __init sysctl_init(void)
>
> base-commit: 94f9b3980dd446b56acf1dfed649e9b32a9f3813
> --
> 2.55.0.508.g3f0d502094-goog
>