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    SubjectRe: [PATCH -next 1/2] mm/slab: add is_kmalloc_cache() helper macro
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    On 11/22/22 06:30, Feng Tang wrote:
    > On Mon, Nov 21, 2022 at 12:19:38PM -0800, Andrew Morton wrote:
    >> On Mon, 21 Nov 2022 21:50:23 +0800 Feng Tang <feng.tang@intel.com> wrote:
    >>
    >> > +#ifndef CONFIG_SLOB
    >> > +#define is_kmalloc_cache(s) ((s)->flags & SLAB_KMALLOC)
    >> > +#else
    >> > +#define is_kmalloc_cache(s) (false)
    >> > +#endif
    >>
    >> Could be implemented as a static inline C function, yes?
    >
    > Right, I also did try inline function first, and met compilation error:
    >
    > "
    > ./include/linux/slab.h: In function ‘is_kmalloc_cache’:
    > ./include/linux/slab.h:159:18: error: invalid use of undefined type ‘struct kmem_cache’
    > 159 | return (s->flags & SLAB_KMALLOC);
    > | ^~
    > "
    >
    > The reason is 'struct kmem_cache' definition for slab/slub/slob sit
    > separately in slab_def.h, slub_def.h and mm/slab.h, and they are not
    > included in this 'include/linux/slab.h'. So I chose the macro way.

    You could try mm/slab.h instead, below the slub_def.h includes there.
    is_kmalloc_cache(s) shouldn't have random consumers in the kernel anyway.
    It's fine if kasan includes it, as it's intertwined with slab a lot anyway.

    > Btw, I've worked on some patches related with sl[auo]b recently, and
    > really felt the pain when dealing with 3 allocators, on both reading
    > code and writing patches. And I really like the idea of fading away
    > SLOB as the first step :)

    Can't agree more :)

    >> If so, that's always best. For (silly) example, consider the behaviour
    >> of
    >>
    >> x = is_kmalloc_cache(s++);
    >>
    >> with and without CONFIG_SLOB.
    >
    > Another solution I can think of is putting the implementation into
    > slab_common.c, like the below?

    The overhead of function call between compilation units (sans LTO) is not
    worth it.

    > Thanks,
    > Feng
    >
    > ---
    > diff --git a/include/linux/slab.h b/include/linux/slab.h
    > index 067f0e80be9e..e4fcdbfb3477 100644
    > --- a/include/linux/slab.h
    > +++ b/include/linux/slab.h
    > @@ -149,6 +149,17 @@
    >
    > struct list_lru;
    > struct mem_cgroup;
    > +
    > +#ifndef CONFIG_SLOB
    > +extern bool is_kmalloc_cache(struct kmem_cache *s);
    > +#else
    > +static inline bool is_kmalloc_cache(struct kmem_cache *s)
    > +{
    > + return false;
    > +}
    > +#endif
    > +
    > /*
    > * struct kmem_cache related prototypes
    > */
    > diff --git a/mm/slab_common.c b/mm/slab_common.c
    > index a5480d67f391..860e804b7c0a 100644
    > --- a/mm/slab_common.c
    > +++ b/mm/slab_common.c
    > @@ -77,6 +77,13 @@ __setup_param("slub_merge", slub_merge, setup_slab_merge, 0);
    > __setup("slab_nomerge", setup_slab_nomerge);
    > __setup("slab_merge", setup_slab_merge);
    >
    > +#ifndef CONFIG_SLOB
    > +bool is_kmalloc_cache(struct kmem_cache *s)
    > +{
    > + return (s->flags & SLAB_KMALLOC);
    > +}
    > +#endif
    > +
    > /*
    > * Determine the size of a slab object
    > */

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