linux-kernel - Re: [PATCH 1/2] alloc_tag: avoid current->alloc_tag manipulations when profiling is disabled

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Message-ID: <CAJuCfpGfSk5_o3ASp3VhmXL1=zRW1krx-6TBdSS83ThDMws+wg@mail.gmail.com>
Date: Thu, 26 Dec 2024 17:09:30 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: akpm@...ux-foundation.org, yuzhao@...gle.com, 00107082@....com, 
	quic_zhenhuah@...cinc.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH 1/2] alloc_tag: avoid current->alloc_tag manipulations
 when profiling is disabled

On Thu, Dec 26, 2024 at 5:07 PM Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> On Thu, Dec 26, 2024 at 4:43 PM Kent Overstreet
> <kent.overstreet@...ux.dev> wrote:
> >
> > On Thu, Dec 26, 2024 at 01:16:38PM -0800, Suren Baghdasaryan wrote:
> > > When memory allocation profiling is disabled there is no need to update
> > > current->alloc_tag and these manipulations add unnecessary overhead. Fix
> > > the overhead by skipping these extra updates.
> >
> > I did it the other way because I was concerned about the overhead of
> > adding a huge number of static keys. But on further thought a static key
> > probably isn't any bigger than an alloc tag, no?
>
> Hmm but a call

Sorry, I pressed enter before finishing typing.

Is a call to static_branch_maybe() generate a new static key? I
thought mem_alloc_profiling_key would be used everywhere but maybe I'm
missing something?

>
> >
> > >
> > > Fixes: b951aaff5035 ("mm: enable page allocation tagging")
> > > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > > Cc: stable@...r.kernel.org
> > > ---
> > >  include/linux/alloc_tag.h | 11 ++++++++---
> > >  lib/alloc_tag.c           |  2 ++
> > >  2 files changed, 10 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
> > > index 0bbbe537c5f9..a946e0203e6d 100644
> > > --- a/include/linux/alloc_tag.h
> > > +++ b/include/linux/alloc_tag.h
> > > @@ -224,9 +224,14 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {}
> > >
> > >  #define alloc_hooks_tag(_tag, _do_alloc)                             \
> > >  ({                                                                   \
> > > -     struct alloc_tag * __maybe_unused _old = alloc_tag_save(_tag);  \
> > > -     typeof(_do_alloc) _res = _do_alloc;                             \
> > > -     alloc_tag_restore(_tag, _old);                                  \
> > > +     typeof(_do_alloc) _res;                                         \
> > > +     if (mem_alloc_profiling_enabled()) {                            \
> > > +             struct alloc_tag * __maybe_unused _old;                 \
> > > +             _old = alloc_tag_save(_tag);                            \
> > > +             _res = _do_alloc;                                       \
> > > +             alloc_tag_restore(_tag, _old);                          \
> > > +     } else                                                          \
> > > +             _res = _do_alloc;                                       \
> > >       _res;                                                           \
> > >  })
> > >
> > > diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> > > index 7dcebf118a3e..4c373f444eb1 100644
> > > --- a/lib/alloc_tag.c
> > > +++ b/lib/alloc_tag.c
> > > @@ -29,6 +29,8 @@ EXPORT_SYMBOL(_shared_alloc_tag);
> > >
> > >  DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
> > >                       mem_alloc_profiling_key);
> > > +EXPORT_SYMBOL(mem_alloc_profiling_key);
> > > +
> > >  DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
> > >
> > >  struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
> > >
> > > base-commit: 431614f1580a03c1a653340c55ea76bd12a9403f
> > > --
> > > 2.47.1.613.gc27f4b7a9f-goog
> > >