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

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

On 2026/8/4 08:30, Suren Baghdasaryan wrote:
> On Mon, Aug 3, 2026 at 2:54 PM 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={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 <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.
> 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.


Agree. The commit message describes it the same way ("page extension 
compression"),

so that needs fixing too.


Thanks

Best Regards

Hao


>
>> +
>> +  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
>> --
>> 2.55.0.508.g3f0d502094-goog
>>