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

[Hao Ge]

On 2026/8/4 08:30, Suren Baghdasaryan wrote:
> On Mon, Aug 3, 2026 at 2:54 PM Abhishek Bapat <abhishekbapat@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >   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