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

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Message-ID: <CAJuCfpGbkp0OPucDLc9bvRZ_SztY0U4DOgAAdfWiTRM7BwCd8w@mail.gmail.com>
Date: Thu, 26 Dec 2024 17:07:10 -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 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

>
> >
> > 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
> >