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

[Hao Ge <hao.ge@linux.dev>]

Hi Abhishek


Subject says "profiling and compression states", but this

patch only adds the compression sysctl. The profiling state was

already exposed via mem_profiling and is untouched here.

I think we should make this more precise, like:

alloc_tag: expose boot-time compression configuration


On 2026/8/4 05:54, Abhishek Bapat 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]').


Profiling state is already readable via mem_profiling. The gap is

only compression. Also, as we discussed, this sysctl reports

what the user requested at boot rather than the actual runtime state.


> 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
> 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.


As this is a standalone patch, please put the v2/v3 changelog below the 
--- line

instead of inside the commit message.


Thanks

Best Regards

Hao


> Signed-off-by: Abhishek Bapat <abhishekbapat@google.com>
> ---
>   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.
> +
> +  0: Page extension compression is disabled.
> +
> +  This control is read-only and reflects the compression status initialized at boot.
> +  Note that, unlike `mem_profiling`, which represents the current state of profiling,
> +  `mem_profiling_compressed` represents the state configured at boot time. Turning off
> +  profiling at runtime will implicitly make this sysctl effectively dormant. However, if
> +  profiling is toggled off and then toggled on again, it will resume with 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_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: 94f9b3980dd446b56acf1dfed649e9b32a9f3813