Re: [PATCH v2] alloc_tag: expose profiling and compression states in /proc/allocinfo

[Hao Ge]

Hi Abhishek


Thanks for the v2 patch.


On 2026/7/31 07:48, 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]').
>
> 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.memprofiling_compressed` to output the
> state.


I think this should be vm.mem_profiling_compressed.

Otherwise, you will need to adjust the procname for this new sysctl 
accordingly.

Also, kindly add docs at the linked path.

https://elixir.bootlin.com/linux/v7.2-rc4/source/Documentation/mm/allocation-profiling.rst#L33


> Signed-off-by: Abhishek Bapat <abhishekbapat@xxxxxxxxxx>
> ---
>   mm/alloc_tag.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> 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,
> +	},
>   };
>   


I think adding this sysctl alone won't be enough.

If we set boot arg sysctl.vm.mem_profiling=1,compressed but profiling 
gets disabled due to insufficient page flags,

this sysctl will still report 1 (compression enabled) even though 
profiling was shut down.

To verify this behavior, I have set up a test environment locally as 
shown below:


[    0.265503] 4046 allocation tags cannot be references using 5 
available page flag bits. Memory allocation profiling is disabled!

[root@localhost ~]# cat /proc/sys/vm/mem_profiling_compressed
1
[root@localhost ~]#


I'm unsure whether we should initialize this sysctl when profiling gets 
disabled at boot.
If we do, we should set mem_profiling_compressed to false in 
shutdown_mem_profiling.


Thanks

Best Regards

Hao


>   static void __init sysctl_init(void)
>
> base-commit: 2ed26e8a624f41887d64e2e37a2f6ab36a118d1f