linux-kernel - Re: [PATCH v4 14/36] lib: add allocation tagging support for memory allocation profiling

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Message-ID: <CAJuCfpEsBEK5M72v1MdSBnh_bFgJLRj3JzDdz1X1BGzfJw6sfw@mail.gmail.com>
Date: Wed, 28 Feb 2024 18:07:18 +0000
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
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Subject: Re: [PATCH v4 14/36] lib: add allocation tagging support for memory
 allocation profiling

On Wed, Feb 28, 2024 at 8:41 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> Another thing I noticed, dunno how critical
>
> On 2/21/24 20:40, Suren Baghdasaryan wrote:
> > +static inline void __alloc_tag_sub(union codetag_ref *ref, size_t bytes)
> > +{
> > +     struct alloc_tag *tag;
> > +
> > +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
> > +     WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n");
> > +#endif
> > +     if (!ref || !ref->ct)
> > +             return;
>
> This is quite careful.
>
> > +
> > +     tag = ct_to_alloc_tag(ref->ct);
> > +
> > +     this_cpu_sub(tag->counters->bytes, bytes);
> > +     this_cpu_dec(tag->counters->calls);
> > +
> > +     ref->ct = NULL;
> > +}
> > +
> > +static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
> > +{
> > +     __alloc_tag_sub(ref, bytes);
> > +}
> > +
> > +static inline void alloc_tag_sub_noalloc(union codetag_ref *ref, size_t bytes)
> > +{
> > +     __alloc_tag_sub(ref, bytes);
> > +}
> > +
> > +static inline void alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *tag)
> > +{
> > +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
> > +     WARN_ONCE(ref && ref->ct,
> > +               "alloc_tag was not cleared (got tag for %s:%u)\n",\
> > +               ref->ct->filename, ref->ct->lineno);
> > +
> > +     WARN_ONCE(!tag, "current->alloc_tag not set");
> > +#endif
> > +     if (!ref || !tag)
> > +             return;
>
> This too.
>
> > +
> > +     ref->ct = &tag->ct;
> > +     /*
> > +      * We need in increment the call counter every time we have a new
> > +      * allocation or when we split a large allocation into smaller ones.
> > +      * Each new reference for every sub-allocation needs to increment call
> > +      * counter because when we free each part the counter will be decremented.
> > +      */
> > +     this_cpu_inc(tag->counters->calls);
> > +}
> > +
> > +static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)
> > +{
> > +     alloc_tag_ref_set(ref, tag);
>
> We might have returned from alloc_tag_ref_set() due to !tag
>
> > +     this_cpu_add(tag->counters->bytes, bytes);
>
> But here we still assume it's valid.

Yes, this is a blunder on my side after splitting alloc_tag_ref_set()
into a separate function. I'll fix this in the next version. Thanks!

>
> > +}
> > +
>
> --
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>