linux-kernel - Re: [PATCH 1/1] alloc_tag: mark inaccurate allocation counters in /proc/allocinfo output

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Message-ID: <902f5f32-2f03-4230-aab0-a886fd8e4793@gmail.com>
Date: Thu, 11 Sep 2025 12:00:23 -0400
From: Usama Arif <usamaarif642@...il.com>
To: Yueyang Pan <pyyjason@...il.com>, David Wang <00107082@....com>,
 Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, kent.overstreet@...ux.dev, vbabka@...e.cz,
 hannes@...xchg.org, rientjes@...gle.com, roman.gushchin@...ux.dev,
 harry.yoo@...cle.com, shakeel.butt@...ux.dev, pasha.tatashin@...een.com,
 souravpanda@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] alloc_tag: mark inaccurate allocation counters in
 /proc/allocinfo output



On 11/09/2025 16:47, Yueyang Pan wrote:
> On Thu, Sep 11, 2025 at 11:03:50PM +0800, David Wang wrote:
>>
>> At 2025-09-10 07:49:42, "Suren Baghdasaryan" <surenb@...gle.com> wrote:
>>> While rare, memory allocation profiling can contain inaccurate counters
>>> if slab object extension vector allocation fails. That allocation might
>>> succeed later but prior to that, slab allocations that would have used
>>> that object extension vector will not be accounted for. To indicate
>>> incorrect counters, mark them with an asterisk in the /proc/allocinfo
>>> output.
>>> Bump up /proc/allocinfo version to reflect change in the file format.
>>>
>>> Example output with invalid counters:
>>> allocinfo - version: 2.0
>>>           0        0 arch/x86/kernel/kdebugfs.c:105 func:create_setup_data_nodes
>>>           0        0 arch/x86/kernel/alternative.c:2090 func:alternatives_smp_module_add
>>>          0*       0* arch/x86/kernel/alternative.c:127 func:__its_alloc
>>>           0        0 arch/x86/kernel/fpu/regset.c:160 func:xstateregs_set
>>>           0        0 arch/x86/kernel/fpu/xstate.c:1590 func:fpstate_realloc
>>>           0        0 arch/x86/kernel/cpu/aperfmperf.c:379 func:arch_enable_hybrid_capacity_scale
>>>           0        0 arch/x86/kernel/cpu/amd_cache_disable.c:258 func:init_amd_l3_attrs
>>>      49152*      48* arch/x86/kernel/cpu/mce/core.c:2709 func:mce_device_create
>>>       32768        1 arch/x86/kernel/cpu/mce/genpool.c:132 func:mce_gen_pool_create
>>>           0        0 arch/x86/kernel/cpu/mce/amd.c:1341 func:mce_threshold_create_device
>>>
>>
>> Hi, 
>> The changes may  break some client tools, mine included.... 
>> I don't mind adjusting my tools, but still
>> Is it acceptable  to change 
>>       49152*      48* arch/x86/kernel/cpu/mce/core.c:2709 func:mce_device_create
>> to
>>       +49152      +48 arch/x86/kernel/cpu/mce/core.c:2709 func:mce_device_create*
>>
>> The '+' sign make it still standout when view from a terminal, and client tools, not all of them though, might not need any changes. 
>> And when client want to filter out inaccurate data items, it could be done by checking the tailing '*" of func name.
> 
> I agree with David on this point. We already have monitoring tool built on top 
> of this output across meta fleet. Ideally we would like to keep the format of 
> of size and calls the same, even for future version, because adding a * will 
> change the format from int to str, which leads to change over the regex parser 
> many places.
> 
> I think simply adding * to the end of function name or filename is sufficient 
> as they are already str.
> 

Instead of:

49152*      48* arch/x86/kernel/cpu/mce/core.c:2709 func:mce_device_create

Could we do something like:

49152      48 arch/x86/kernel/cpu/mce/core.c:2709 func:mce_device_create(inaccurate)

This should hopefully not require any changes to the tools that are consuming this file.
I think it might be better to use "(inaccurate)" (without any space after function name) or
some other text instead of "+" or "*" to prevent breaking such tools. I dont think we need
to even increment allocinfo version number as well then?

>>
>> (There would be some corner cases, for example, the '+' sign may not needed when the value reach a negative value if some underflow bug happened)
>>
>>
>> Thanks
>> David.
>>
>>
>>> Suggested-by: Johannes Weiner <hannes@...xchg.org>
>>> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>>> ---
>>
> 
> Thanks
> Pan