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Message-ID: <CAJuCfpE=0jpana5qryqwPsuoj_8tCEMWFMcEBTB5-9Lyu_j-Tw@mail.gmail.com> Date: Thu, 11 Sep 2025 11:13:58 -0700 From: Suren Baghdasaryan <surenb@...gle.com> To: David Wang <00107082@....com> Cc: Yueyang Pan <pyyjason@...il.com>, Usama Arif <usamaarif642@...il.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 10:35 AM David Wang <00107082@....com> wrote: > > > At 2025-09-12 01:25:05, "Yueyang Pan" <pyyjason@...il.com> wrote: > >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. Uh, right. We do have module name as an optional field... > > The inconsistent of module name is really inconvenient for parsing..... > Could we make changes to make it consistent, something like: > > diff --git a/lib/codetag.c b/lib/codetag.c > index 545911cebd25..b8a4595adc95 100644 > --- a/lib/codetag.c > +++ b/lib/codetag.c > @@ -124,7 +124,7 @@ void codetag_to_text(struct seq_buf *out, struct codetag *ct) > ct->filename, ct->lineno, > ct->modname, ct->function); > else > - seq_buf_printf(out, "%s:%u func:%s", > + seq_buf_printf(out, "%s:%u [kernel] func:%s", Yeah, until someone creates a module called "kernel" :) We could keep the name empty like this: + seq_buf_printf(out, "%s:%u [] func:%s", but I'm not sure that's the best solution. If we are really concerned about parsers, I could add an ioctl interface to query the counters which are inaccurate. Would that be better? BTW, I have other ideas for ioctls, like filtering-out 0-sized allocations and such. > ct->filename, ct->lineno, ct->function); > } > > > > > > > >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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