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

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

Hi Abhishek


Thanks for your patch.


On 2026/7/30 06:49, 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.
> Furthermore, since /proc/allocinfo remains in the procfs filesystem even
> after profiling is dynamically disabled at runtime, simply checking for
> the file's presence does not reliably indicate if the allocation
> tracking hooks are actively running.
>
> Resolve this ambiguity by appending the active state directly into the
> header of /proc/allocinfo.


It's not obvious to me why userspace would need this state.


Suppose userspace reads mem_alloc_profiling_enabled as disabled, then 
the profiling

gets enabled later. All allocations generated during that intermediate 
window are lost.

When users later cat /proc/allocinfo and see the enabled state, will 
they mistakenly take

the output as a complete, accurate record?


I'm also unclear what userspace would do with the compression state;

this is just an internal implementation detail of memory profiling.

Put another way, personally I'd prefer /proc/allocinfo to stay lean and

avoid exposing too many internal implementation details to userspace.

Unless users intend to dig deep into how memory profiling works, these 
extra details

will likely only confuse them — most don't care about internals at all.

It's similar to how we use APIs: we only care about what an API achieves,

not its underlying implementation.


Could you share the concrete use cases for exposing these states to 
userspace?


Thanks

Best Regards

Hao


> Signed-off-by: Abhishek Bapat <abhishekbapat@google.com>
> ---
>   mm/alloc_tag.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
> index 52aece27b00e..89ec2c6ce57a 100644
> --- a/mm/alloc_tag.c
> +++ b/mm/alloc_tag.c
> @@ -108,7 +108,11 @@ static void allocinfo_stop(struct seq_file *m, void *arg)
>   static void print_allocinfo_header(struct seq_buf *buf)
>   {
>   	/* Output format version, so we can change it. */
> -	seq_buf_printf(buf, "allocinfo - version: 2.0\n");
> +	seq_buf_printf(buf, "allocinfo - version: 2.1\n");
> +	seq_buf_printf(buf, "# Profiling: %s\n",
> +		       mem_alloc_profiling_enabled() ? "Enabled" : "Disabled");
> +	seq_buf_printf(buf, "# Compression: %s\n",
> +		       static_key_enabled(&mem_profiling_compressed) ? "Enabled" : "Disabled");
>   	seq_buf_printf(buf, "#     <size>  <calls> <tag info>\n");
>   }
>   
>
> base-commit: c73b725a57f276a3702ca213bde78fca029bc619