Message-ID: <aMMF8elYvlPoOF+J@devbig569.cln6.facebook.com>
Date: Thu, 11 Sep 2025 10:25:05 -0700
From: Yueyang Pan <pyyjason@...il.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Usama Arif <usamaarif642@...il.com>, David Wang <00107082@....com>,
	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 Thu, Sep 11, 2025 at 09:18:29AM -0700, Suren Baghdasaryan wrote:
> On Thu, Sep 11, 2025 at 9:00 AM Usama Arif <usamaarif642@...il.com> wrote:
> >
> >
> >
> > 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)
> 
> If there is a postprocessing then this would break sometimes later
> when the function name is parsed, right? So IMO that just postpones
> the breakage.
> 
> >
> > 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?
> 
> I'm wondering if we add a new column at the end like this:
> 
> 49152      48 arch/x86/kernel/cpu/mce/core.c:2709
> func:mce_device_create [inaccurate]
> 
> would that break the parsing tools?
> Well-designed parsers usually throw away additional fields which they
> don't know how to parse. WDYT?
> 

It would break the parse now as we count the number of string to decide if 
there is an optional module name or not. I don't think it is a big 
deal to fix though.

I think one more important thing is probably to reach a consensus on 
what format can be changed in the future, for example say, we can 
keep adding columns but not change the format the type of one column.
With such consensus in mind, it will be easier to design the parser. 
And I guess many companies will build parser upon this info for fleet-
wise collection.

> >
> > >>
> > >> (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
> >

Thanks
Pan

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