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

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Message-ID: <aMLvCCZbmpSE/aql@devbig569.cln6.facebook.com>
Date: Thu, 11 Sep 2025 08:47:20 -0700
From: Yueyang Pan <pyyjason@...il.com>
To: David Wang <00107082@....com>
Cc: Suren Baghdasaryan <surenb@...gle.com>, akpm@...ux-foundation.org,
	kent.overstreet@...ux.dev, vbabka@...e.cz, hannes@...xchg.org,
	usamaarif642@...il.com, 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 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.

> 
> (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