[PATCH v3] alloc_tag: expose profiling and compression states

[PATCH v3] alloc_tag: expose profiling and compression states

[Abhishek Bapat]

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
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.
+
+  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

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

[Suren Baghdasaryan]

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.

> +
> +  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
>

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@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
>>

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

[Hao Ge]

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

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

[Hao Ge]

On 2026/8/4 10:15, Hao Ge wrote:
> 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.


Sorry, I forgot to mention this earlier.

I wonder if we could remove this section:


>> 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.


mem_profiling_compressed only selects the tag storage format (page flags 
vs page_ext).

mem_profiling controls whether allocations are tagged at runtime.

The two are independent: toggling mem_profiling on/off has no effect on

compression. Only shutdown_mem_profiling() tears it down, but by then

the entire allocation profiling subsystem is disabled anyway. There is

no resume path.


>> +
>>   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

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

[Abhishek Bapat]

On Mon, Aug 3, 2026 at 9:14 PM Hao Ge <hao.ge@linux.dev> wrote:
>
>
> On 2026/8/4 10:15, Hao Ge wrote:
> > 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.
>
>
> Sorry, I forgot to mention this earlier.
>
> I wonder if we could remove this section:
>
>
> >> 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.
>
>
> mem_profiling_compressed only selects the tag storage format (page flags
> vs page_ext).
>
> mem_profiling controls whether allocations are tagged at runtime.
>
> The two are independent: toggling mem_profiling on/off has no effect on
>
> compression. Only shutdown_mem_profiling() tears it down, but by then
>
> the entire allocation profiling subsystem is disabled anyway. There is
>
> no resume path.
>
>

I added this based on Suren's comment on the previous version asking
me to explicitly describe the behaviour in the Documentation. The
original version did not contain it. But personally I do think keeping
this here makes sense.

> >> +
> >>   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

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

[Abhishek Bapat]

On Tue, Aug 4, 2026 at 10:28 AM Abhishek Bapat <abhishekbapat@google.com> wrote:
>
> On Mon, Aug 3, 2026 at 9:14 PM Hao Ge <hao.ge@linux.dev> wrote:
> >
> >
> > On 2026/8/4 10:15, Hao Ge wrote:
> > > 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.
> >
> >
> > Sorry, I forgot to mention this earlier.
> >
> > I wonder if we could remove this section:
> >
> >
> > >> 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.
> >
> >
> > mem_profiling_compressed only selects the tag storage format (page flags
> > vs page_ext).
> >
> > mem_profiling controls whether allocations are tagged at runtime.
> >
> > The two are independent: toggling mem_profiling on/off has no effect on
> >
> > compression. Only shutdown_mem_profiling() tears it down, but by then
> >
> > the entire allocation profiling subsystem is disabled anyway. There is
> >
> > no resume path.
> >
> >
>
> I added this based on Suren's comment on the previous version asking
> me to explicitly describe the behaviour in the Documentation. The
> original version did not contain it. But personally I do think keeping
> this here makes sense.
>

I checked in with Suren offline and he suggested I reword the
description to make it simpler to understand. I'll shortly send out a
v4 patch with updated documentation. Thanks!

> > >> +
> > >>   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